diff --git a/README.MD b/README.MD
index 21df361..5ebca81 100644
--- a/README.MD
+++ b/README.MD
@@ -37,9 +37,21 @@ vr clean                                    remove .vobj/.vbin artifacts
 vr up                                       rebuild bin/vr
 vr symlink                                  link bin/vr into your PATH
 vr config [set <key> <value>]               toolchain config (outdir, verbose)
+vr repl                                     interactive session
+vr fmt [-w] <file.vr>                       format source (keeps comments)
+vr init [name]                              scaffold a project (vr.mod + main.vr)
+vr get <owner/repo | git-url | ./path>      fetch a package into vendor/
+vr install                                  install dependencies from vr.mod
+vr list                                     show the project manifest
 vr info | loader | alloc | version | help
 ```
 
+```bash
+./bin/vr repl          # try expressions and functions interactively
+./bin/vr fmt -w f.vr   # normalize a file's indentation/spacing in place
+./bin/vr init myproj   # start a project; vr get owner/repo fetches packages
+```
+
 Quick start:
 
 ```bash
@@ -61,9 +73,10 @@ Quick start:
 
 ## The VuurRaaf language
 
-A small, V-flavored language. Values are 64-bit integers, strings, arrays, or
-structs (strings concatenate with `+` and compare with `==`/`!=`; arrays and
-structs are mutable references that compare by identity).
+A small, V-flavored language. Values are 64-bit integers, 64-bit floats,
+strings, arrays, structs, enums, and closures (strings concatenate with `+`
+and compare with `==`/`!=`; arrays and structs are mutable references that
+compare by identity).
 
 ```
 fn sum(items) {
@@ -138,10 +151,29 @@ fn main() {
 }
 ```
 
-- functions: `fn name(a, b) { ... }` with `return expr`
+- functions: `fn name(a, b) { ... }` with `return expr`; default parameter
+  values `fn f(a, b = 10)`, variadic params `fn f(nums...)`, destructuring
+  `let { a, b } = rec` and `let [x, y] = arr`, and anonymous closures
+  `let f = fn(x) { return x * 2 }` stored in variables and arrays
+- generics: `fn first[T](arr) { return arr[0] }` with checked call sites
+  `first[int](arr)` — the VM is dynamically typed, so type parameters erase
+  to a single function but arity and duplicates are validated
 - variables: `let name = expr`, reassignment `name = expr`
+- floats: `3.14`, `0.5`, `1e3` — float literals and `float(x)`; arithmetic
+  promotes to float; `floor` / `ceil` / `round` / `sqrt` / `pow` / `abs` /
+  `min` / `max` / `rand` / `rand_int`
+- strings are UTF-8: `len(s)` counts characters, `s[i]` and `s[a..b]` index
+  and slice by character (runes), and methods like `s.to_upper()`,
+  `s.contains(x)`, `s.split(d)`, `s.index_of(x)`, `s.to_int()`, `s.len()`
+  work on any string-valued expression
 - arrays: `[e1, e2, ...]`, indexing `a[i]` (read and write), `len(a)`,
-  `push(a, v)`; array literals may nest
+  `push/insert/remove/pop/sort/reverse/clone/index_of/join`; array literals
+  may nest
+- error handling: `try { ... } catch e { ... }` and `throw "message"` — the
+  runtime unwinds to the nearest catch
+- bitwise operators: `& | ^ ~ << >>`
+- host builtins: `read_file` / `write_file`, `args()`, `getenv` / `setenv`,
+  `exit`, `sleep`, `time()`, `type(x)`, `str(x)`, `int(x)`, `split` / `join`
 - for loops: `for x in arr { }` and ranges `for i in 0..10 { }` /
   `for i in 0...10 { }`; loop variables are scoped to the loop body
 - `break` / `continue` inside `while` and `for` loops (in `for` loops
@@ -153,9 +185,14 @@ fn main() {
   field access `a.b` and assignment `a.b = v` (chained: `a[i].b`, `a.b[i]`);
   structs are mutable references (identity `==`/`!=`), and setting a missing
   field adds it, so records can be built incrementally
-- operators: `+ - * / %`, `== != < <= > >=`, `and or not`, unary `-`
+- enums: `enum Color { red green blue }` with `Color.red`, `e.to_string()`,
+  `e.count()`, and iteration in `for`
+- constants: `const NAME = 42` (compile-time integer/bool values)
+- operators: `+ - * / %`, `== != < <= > >=`, `and or not`, `& | ^ ~ << >>`,
+  unary `-`; constant expressions fold at compile time
 - statements: `let`, assignment, `if/else`, `match`, `while`, `for`,
-  `break`, `continue`, `return`, `assert`, calls, `print(...)` / `println(...)`
+  `break`, `continue`, `return`, `assert`, `try/catch`/`throw`, calls,
+  `print(...)` / `println(...)`
 - comments: `//`
 
 ## Assembly
@@ -198,25 +235,32 @@ field name as a string first, exactly like the compiler does).
 
 | module       | role                                                        |
 |--------------|-------------------------------------------------------------|
-| `compiler/`  | lexer, recursive-descent parser, bytecode codegen (VROBJ)   |
+| `compiler/`  | lexer, parser, type checker, bytecode codegen (VROBJ)      |
 | `assembler/` | `.vasm` -> VROBJ                                            |
 | `linker/`    | resolves relocations, rebases strings, emits VRBIN          |
 | `vm/`        | stack VM: tagged values, call frames, string/array heaps    |
 | `obj/`       | VROBJ/VRBIN binary formats                                  |
 | `bin/`       | small standalone tools: `tl_alloc.v`, `tl_loader.v`         |
 
-The VM is a stack machine with 64-bit tagged values using two tag bits:
-numbers are stored shifted left by two, string handles end in `01`, array
-handles in `11` — so no integer ever collides with a heap handle. Arrays live
-in a growable heap (`mkarray`/`aget`/`aset`/`alen`/`apush`). Calls push a
-frame (return address, base pointer, argc), copy arguments into local slots,
-and reserve extra locals with `enter n`. `vr debug` prints every instruction
-with the stack contents (arrays rendered as `[1, 2, ...]`).
+The VM is a stack machine with 64-bit tagged values using three tag bits:
+ints, string/array/struct/float/closure handles — so no integer ever
+collides with a heap handle. A mark-and-sweep garbage collector runs between
+opcodes when the heap grows past a threshold, tracing the stack (which holds
+every frame's locals) and compacting the pools; string constants baked into
+bytecode are never collected. Bytecode carries a line table, so runtime
+errors report the source line. A conservative compile-time type checker
+(`compiler/check.v`) rejects provably wrong programs (unknown variables,
+field access on numbers, arithmetic on strings, wrong arity) while leaving
+dynamic programs alone. `vr debug` prints every instruction with the stack
+contents (arrays rendered as `[1, 2, ...]`).
 
 ## Repository layout
 
 ```
 main.v               CLI entry point (vr <command> ...)
+repl.v               interactive REPL
+fmt.v                source formatter
+pkg.v                package manager (init/get/install/list)
 v.mod                module definition
 compiler/ assembler/ linker/ vm/ obj/   the toolchain itself
 bin/                 built binary + standalone tools
diff --git a/compiler/ast.v b/compiler/ast.v
index 085080b..e1bdd3b 100644
--- a/compiler/ast.v
+++ b/compiler/ast.v
@@ -3,6 +3,7 @@ module compiler
 
 pub enum ExprKind {
 	int_lit
+	float_lit
 	str_lit
 	bool_lit
 	ident
@@ -11,7 +12,9 @@ pub enum ExprKind {
 	index
 	field
 	method_call
+	slice
 	unary
+	anon_fn
 	binary
 	call
 }
@@ -25,22 +28,31 @@ pub mut:
 
 pub struct Expr {
 pub mut:
-	kind   ExprKind
-	int_v  i64
-	str_v  string
+	kind    ExprKind
+	int_v   i64
+	float_v f64
+	str_v   string
 	name   string // ident/call name, or the field name of a `.field` access
 	op     TokKind
 	left   &Expr = unsafe { nil }
 	right  &Expr = unsafe { nil }
+	extra  &Expr = unsafe { nil } // slice: end index expression
 	elems  []Expr
 	fields []StructField // struct_lit: the named fields
-	args   []Expr
-	line   int
+	args     []Expr
+	type_args []string // call: explicit generic type arguments (first[int](...))
+	fparams  []string // anon_fn: parameter names
+	fdefaults []Expr  // anon_fn: default values (parallel to fparams)
+	fhas_defs []bool  // anon_fn: which params have defaults
+	fvariadic bool    // anon_fn: last param is variadic
+	fn_body  []Stmt   // anon_fn: function body
+	line     int
 }
 
 pub enum StmtKind {
 	expr_stmt
 	let_stmt
+	destruct_stmt
 	assign_stmt
 	index_assign
 	field_assign
@@ -53,6 +65,8 @@ pub enum StmtKind {
 	continue_stmt
 	ret_stmt
 	assert_stmt
+	try_stmt
+	throw_stmt
 }
 
 // MatchArm is a single `value { body }` arm of a match statement.
@@ -66,6 +80,9 @@ pub struct Stmt {
 pub mut:
 	kind      StmtKind
 	target    string
+	idx_target string // for_in_stmt: index variable name (empty when unused)
+	destruct_targets []string // destruct_stmt: names to bind
+	destruct_field   bool     // destruct_stmt: struct ({ a, b }) vs array ([a, b])
 	expr      Expr
 	cond      Expr
 	base      Expr // index_assign: the indexed expression
@@ -90,10 +107,14 @@ pub mut:
 
 pub struct FnDecl {
 pub mut:
-	name      string
-	recv_name string // method receiver local name ('' for plain functions)
-	recv_type string // method receiver struct type ('' for plain functions)
+	name       string
+	type_params []string // generic type parameters (fn first[T, U](...) { ... })
+	recv_name  string // method receiver local name ('' for plain functions)
+	recv_type  string // method receiver struct type ('' for plain functions)
 	params    []string
+	defaults  []Expr // parallel to params; empty Expr{} when no default
+	has_defs  []bool // parallel to params: whether a default exists
+	variadic  bool   // last param is variadic (nums...)
 	body      []Stmt
 	line      int
 }
@@ -120,11 +141,28 @@ pub mut:
 	line  int
 }
 
+// InterfaceDecl is an `interface Name { method1(); method2() type }` declaration.
+// Methods are stored as (name, return_type) pairs. The interface is satisfied
+// by any struct that implements all listed methods (structural/duck typing).
+pub struct InterfaceDecl {
+pub mut:
+	name    string
+	methods []InterfaceMethod
+	line    int
+}
+
+pub struct InterfaceMethod {
+pub mut:
+	name string
+	line int
+}
+
 pub struct Program {
 pub mut:
-	fns     []FnDecl
-	structs []StructDecl
-	enums   []EnumDecl
-	imports []ImportDecl
-	consts  []ConstDecl
+	fns        []FnDecl
+	structs    []StructDecl
+	enums      []EnumDecl
+	imports    []ImportDecl
+	consts     []ConstDecl
+	interfaces []InterfaceDecl
 }
diff --git a/compiler/check.v b/compiler/check.v
new file mode 100644
index 0000000..6d22f5d
--- /dev/null
+++ b/compiler/check.v
@@ -0,0 +1,599 @@
+// check.v — a compile-time type checker for VuurRaaf.
+//
+// Runs after parsing and before codegen. The language is dynamically typed at
+// runtime, so this pass is deliberately conservative: it rejects programs that
+// are *provably* wrong (unknown variables, field access on numbers, arithmetic
+// on strings, wrong arity on known functions) while leaving genuinely dynamic
+// programs (untyped parameters, unknown receiver types, mixed containers, and
+// calls to functions defined in other objects) alone. Unresolved function
+// names are deferred to the linker, matching the toolchain's separate
+// compilation model.
+module compiler
+
+import os
+
+enum CType {
+	unknown
+	int_t
+	float_t
+	string_t
+	bool_t
+	array_t
+	struct_t
+	enum_t
+	closure_t
+}
+
+struct TypeInfo {
+	kind CType
+	name string // struct/enum type name when statically known
+}
+
+struct FnSig {
+	min_args      int
+	has_defs      []bool
+	variadic      bool
+	n_type_params int // generic type parameters declared on the function
+	returns       TypeInfo
+}
+
+struct Checker {
+mut:
+	types   map[string]TypeInfo // current scope: local name -> type
+	fns     map[string]FnSig
+	structs map[string][]string
+	enums   map[string][]string
+	consts  map[string]TypeInfo
+	loop_depth int
+	checked map[string]bool // imported files already checked
+}
+
+// check validates a parsed program and returns an error on the first problem.
+fn check(prog Program) ! {
+	mut c := Checker{}
+	// register declarations
+	for sd in prog.structs {
+		if sd.name in c.structs {
+			return error('duplicate struct declaration "${sd.name}" (line ${sd.line})')
+		}
+		c.structs[sd.name] = sd.fields
+	}
+	for ed in prog.enums {
+		if ed.name in c.enums {
+			return error('duplicate enum declaration "${ed.name}" (line ${ed.line})')
+		}
+		c.enums[ed.name] = ed.variants
+	}
+	for cd in prog.consts {
+		c.consts[cd.name] = TypeInfo{ kind: .int_t }
+	}
+	for fd in prog.fns {
+		if fd.name in c.fns {
+			return error('duplicate function "${fd.name}" (line ${fd.line})')
+		}
+		c.fns[fd.name] = FnSig{ min_args: fd.params.len - def_count(fd), has_defs: fd.has_defs, variadic: fd.variadic, n_type_params: fd.type_params.len }
+	}
+	// imported files are checked (and their symbols merged) recursively
+	for imp in prog.imports {
+		c.check_import(imp.path)!
+	}
+	for fd in prog.fns {
+		c.check_fn(fd)!
+	}
+}
+
+fn def_count(fd FnDecl) int {
+	mut n := 0
+	for has in fd.has_defs {
+		if has {
+			n++
+		}
+	}
+	return n
+}
+
+fn (mut c Checker) check_import(path string) ! {
+	if path in c.checked {
+		return
+	}
+	c.checked[path] = true
+	resolved := resolve_import(path) or { return error('cannot read import "${path}"') }
+	src := os.read_file(resolved) or { return error('cannot read import "${path}"') }
+	prog := parse(tokenize(src)!)!
+	// merge declarations from the import
+	for sd in prog.structs {
+		if sd.name !in c.structs {
+			c.structs[sd.name] = sd.fields
+		}
+	}
+	for ed in prog.enums {
+		if ed.name !in c.enums {
+			c.enums[ed.name] = ed.variants
+		}
+	}
+	for cd in prog.consts {
+		if cd.name !in c.consts {
+			c.consts[cd.name] = TypeInfo{ kind: .int_t }
+		}
+	}
+	for fd in prog.fns {
+		if fd.name !in c.fns {
+			c.fns[fd.name] = FnSig{ min_args: fd.params.len - def_count(fd), has_defs: fd.has_defs, variadic: fd.variadic, n_type_params: fd.type_params.len }
+		}
+	}
+	for imp in prog.imports {
+		c.check_import(imp.path)!
+	}
+	for fd in prog.fns {
+		c.check_fn(fd)!
+	}
+}
+
+fn (mut c Checker) check_fn(fd FnDecl) ! {
+	c.types.clear()
+	c.loop_depth = 0
+	// receiver and parameters are untyped (unknown) — the runtime is dynamic
+	if fd.recv_name.len > 0 {
+		c.types[fd.recv_name] = TypeInfo{ kind: .struct_t }
+	}
+	for p in fd.params {
+		c.types[p] = TypeInfo{ kind: .unknown }
+	}
+	for st in fd.body {
+		c.check_stmt(st)!
+	}
+}
+
+fn (mut c Checker) check_stmt(st Stmt) ! {
+	match st.kind {
+		.expr_stmt {
+			_ = c.check_expr(st.expr)!
+		}
+		.let_stmt {
+			t := c.check_expr(st.expr)!
+			c.types[st.target] = t
+		}
+		.destruct_stmt {
+			base := c.check_expr(st.expr)!
+			for name in st.destruct_targets {
+				c.types[name] = if st.destruct_field { TypeInfo{ kind: .unknown } } else { TypeInfo{ kind: .unknown } }
+			}
+			_ = base
+		}
+		.assign_stmt {
+			if st.target !in c.types {
+				return error('unknown variable "${st.target}" (line ${st.line})')
+			}
+			_ = c.check_expr(st.expr)!
+		}
+		.index_assign {
+			base := c.check_expr(st.base)!
+			_ = c.check_expr(st.idx)!
+			c.expect_container(base, 'index assignment', st.line)!
+			_ = c.check_expr(st.expr)!
+		}
+		.field_assign {
+			base := c.check_expr(st.base)!
+			c.expect_struct_like(base, 'field assignment', st.line)!
+			_ = c.check_expr(st.expr)!
+		}
+		.if_stmt {
+			_ = c.check_expr(st.cond)!
+			for s in st.body {
+				c.check_stmt(s)!
+			}
+			for s in st.els {
+				c.check_stmt(s)!
+			}
+		}
+		.match_stmt {
+			_ = c.check_expr(st.expr)!
+			for arm in st.arms {
+				_ = c.check_expr(arm.val)!
+				for s in arm.body {
+					c.check_stmt(s)!
+				}
+			}
+			for s in st.els_body {
+				c.check_stmt(s)!
+			}
+		}
+		.while_stmt {
+			_ = c.check_expr(st.cond)!
+			c.loop_depth++
+			for s in st.body {
+				c.check_stmt(s)!
+			}
+			c.loop_depth--
+		}
+		.for_range_stmt {
+			start_t := c.check_expr(st.expr)!
+			end_t := c.check_expr(st.cond)!
+			c.expect_numeric(start_t, 'range start', st.line)!
+			c.expect_numeric(end_t, 'range end', st.line)!
+			c.types[st.target] = TypeInfo{ kind: .int_t }
+			c.loop_depth++
+			for s in st.body {
+				c.check_stmt(s)!
+			}
+			c.loop_depth--
+		}
+		.for_in_stmt {
+			seq := c.check_expr(st.expr)!
+			// iterate enums and arrays; unknown is allowed (dynamic)
+			if seq.kind == .int_t || seq.kind == .float_t || seq.kind == .bool_t {
+				return error('cannot iterate a ${type_name(seq.kind)} (line ${st.line})')
+			}
+			c.types[st.target] = TypeInfo{ kind: .unknown }
+			if st.idx_target.len > 0 {
+				c.types[st.idx_target] = TypeInfo{ kind: .int_t }
+			}
+			c.loop_depth++
+			for s in st.body {
+				c.check_stmt(s)!
+			}
+			c.loop_depth--
+		}
+		.break_stmt, .continue_stmt {
+			if c.loop_depth == 0 {
+				what := if st.kind == .break_stmt { 'break' } else { 'continue' }
+				return error('${what} outside of a loop (line ${st.line})')
+			}
+		}
+		.ret_stmt {
+			if st.has_val {
+				_ = c.check_expr(st.expr)!
+			}
+		}
+		.assert_stmt {
+			_ = c.check_expr(st.expr)!
+		}
+		.try_stmt {
+			c.loop_depth++ // errors unwind through loops; keep depth permissive
+			c.loop_depth--
+			for s in st.body {
+				c.check_stmt(s)!
+			}
+			c.types[st.target] = TypeInfo{ kind: .string_t }
+			for s in st.els {
+				c.check_stmt(s)!
+			}
+		}
+		.throw_stmt {
+			_ = c.check_expr(st.expr)!
+		}
+	}
+}
+
+fn (mut c Checker) check_expr(e Expr) !TypeInfo {
+	return match e.kind {
+		.int_lit { TypeInfo{ kind: .int_t } }
+		.float_lit { TypeInfo{ kind: .float_t } }
+		.str_lit { TypeInfo{ kind: .string_t } }
+		.bool_lit { TypeInfo{ kind: .bool_t } }
+		.ident {
+			if e.name in c.types {
+				c.types[e.name]
+			} else if e.name in c.consts {
+				c.consts[e.name]
+			} else {
+				return error('unknown variable "${e.name}" (line ${e.line})')
+			}
+		}
+		.array_lit {
+			for el in e.elems {
+				_ = c.check_expr(el)!
+			}
+			TypeInfo{ kind: .array_t }
+		}
+		.struct_lit {
+			if e.name.len > 0 && e.name in c.structs {
+				fields := c.structs[e.name]
+				mut seen := map[string]bool{}
+				for f in e.fields {
+					if f.name !in fields {
+						return error('unknown field "${f.name}" for struct ${e.name} (line ${e.line})')
+					}
+					if f.name in seen {
+						return error('duplicate field "${f.name}" in struct literal (line ${e.line})')
+					}
+					seen[f.name] = true
+					_ = c.check_expr(f.val)!
+				}
+				return TypeInfo{ kind: .struct_t, name: e.name }
+			}
+			for f in e.fields {
+				_ = c.check_expr(f.val)!
+			}
+			TypeInfo{ kind: .struct_t }
+		}
+		.index {
+			base := c.check_expr(*e.left)!
+			_ = c.check_expr(*e.right)!
+			c.expect_container(base, 'indexing', e.line)!
+			TypeInfo{ kind: .unknown }
+		}
+		.field {
+			base := c.check_expr(*e.left)!
+			c.expect_struct_like(base, 'field access', e.line)!
+			// enum variant: Color.red  →  enum_t
+			if base.kind == .enum_t {
+				return TypeInfo{ kind: .enum_t, name: base.name }
+			}
+			TypeInfo{ kind: .unknown }
+		}
+		.method_call {
+			recv := c.check_expr(*e.left)!
+			if recv.kind == .int_t || recv.kind == .float_t || recv.kind == .bool_t {
+				return error('cannot call a method on a ${type_name(recv.kind)} (line ${e.line})')
+			}
+			for a in e.args {
+				_ = c.check_expr(a)!
+			}
+			TypeInfo{ kind: .unknown }
+		}
+		.slice {
+			base := c.check_expr(*e.left)!
+			_ = c.check_expr(*e.right)!
+			_ = c.check_expr(*e.extra)!
+			if base.kind == .int_t || base.kind == .float_t || base.kind == .bool_t {
+				return error('cannot slice a ${type_name(base.kind)} (line ${e.line})')
+			}
+			if base.kind == .string_t {
+				TypeInfo{ kind: .string_t }
+			} else {
+				TypeInfo{ kind: .unknown }
+			}
+		}
+		.unary {
+			op := c.check_expr(*e.right)!
+			match e.op {
+				.kw_not { TypeInfo{ kind: .bool_t } }
+				.tilde {
+					c.expect_int(op, 'bitwise not', e.line)!
+					TypeInfo{ kind: .int_t }
+				}
+				else {
+					c.expect_numeric(op, 'unary minus', e.line)!
+					op
+				}
+			}
+		}
+		.binary {
+			c.check_binary(e)!
+		}
+		.call {
+			c.check_call(e)!
+		}
+		.anon_fn {
+			for p in e.fparams {
+				c.types[p] = TypeInfo{ kind: .unknown }
+			}
+			for s in e.fn_body {
+				c.check_stmt(s)!
+			}
+			TypeInfo{ kind: .closure_t }
+		}
+	}
+}
+
+fn (mut c Checker) check_binary(e Expr) !TypeInfo {
+	l := c.check_expr(*e.left)!
+	r := c.check_expr(*e.right)!
+	return match e.op {
+		.plus {
+			if l.kind == .string_t || r.kind == .string_t {
+				return TypeInfo{ kind: .string_t }
+			}
+			if l.kind == .array_t || r.kind == .array_t {
+				return error('cannot add arrays with + (line ${e.line})')
+			}
+			if l.kind == .struct_t || r.kind == .struct_t {
+				return error('cannot add structs with + (line ${e.line})')
+			}
+			if l.kind == .bool_t || r.kind == .bool_t {
+				return error('cannot add a bool with + (line ${e.line})')
+			}
+			if l.kind == .unknown || r.kind == .unknown {
+				return TypeInfo{ kind: .unknown }
+			}
+			if l.kind == .float_t || r.kind == .float_t {
+				return TypeInfo{ kind: .float_t }
+			}
+			return TypeInfo{ kind: .int_t }
+		}
+		.minus, .star, .slash, .percent {
+			c.expect_numeric(l, 'arithmetic', e.line)!
+			c.expect_numeric(r, 'arithmetic', e.line)!
+			if l.kind == .float_t || r.kind == .float_t {
+				TypeInfo{ kind: .float_t }
+			} else {
+				TypeInfo{ kind: .int_t }
+			}
+		}
+		.eq_eq, .not_eq {
+			TypeInfo{ kind: .bool_t }
+		}
+		.lt, .le, .gt, .ge {
+			if l.kind == .array_t || r.kind == .array_t {
+				return error('cannot order arrays (line ${e.line})')
+			}
+			if l.kind == .struct_t || r.kind == .struct_t {
+				return error('cannot order structs (line ${e.line})')
+			}
+			if l.kind == .bool_t && r.kind == .bool_t {
+				return error('cannot order booleans (line ${e.line})')
+			}
+			if l.kind != .unknown && r.kind != .unknown && l.kind != r.kind && !(is_num_kind(l.kind) && is_num_kind(r.kind)) {
+				return error('cannot compare a ${type_name(l.kind)} and a ${type_name(r.kind)} (line ${e.line})')
+			}
+			TypeInfo{ kind: .bool_t }
+		}
+		.kw_and, .kw_or {
+			TypeInfo{ kind: .bool_t }
+		}
+		.amp, .pipe, .caret, .lt_lt, .gt_gt {
+			c.expect_int(l, 'bitwise operator', e.line)!
+			c.expect_int(r, 'bitwise operator', e.line)!
+			TypeInfo{ kind: .int_t }
+		}
+		else {
+			return error('unsupported operator at line ${e.line}')
+		}
+	}
+}
+
+fn (mut c Checker) check_call(e Expr) !TypeInfo {
+	// builtin calls
+	if e.name == 'len' {
+		if e.args.len != 1 {
+			return error('len() takes exactly one argument (line ${e.line})')
+		}
+		t := c.check_expr(e.args[0])!
+		if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .closure_t {
+			return error('len() on a ${type_name(t.kind)} (line ${e.line})')
+		}
+		return TypeInfo{ kind: .int_t }
+	}
+	if e.name == 'push' || e.name == 'insert' || e.name == 'remove' {
+		if e.args.len == 0 {
+			return error('${e.name}() expects arguments (line ${e.line})')
+		}
+		seq := c.check_expr(e.args[0])!
+		c.expect_container(seq, '${e.name}()', e.line)!
+		for a in e.args[1..] {
+			_ = c.check_expr(a)!
+		}
+		return TypeInfo{ kind: .unknown }
+	}
+	if e.name == 'has' || e.name == 'delete' {
+		if e.args.len != 2 {
+			return error('${e.name}() takes exactly two arguments (line ${e.line})')
+		}
+		seq := c.check_expr(e.args[0])!
+		c.expect_struct_like(seq, '${e.name}()', e.line)!
+		_ = c.check_expr(e.args[1])!
+		return TypeInfo{ kind: .unknown }
+	}
+	if e.name == 'keys' {
+		if e.args.len != 1 {
+			return error('keys() takes exactly one argument (line ${e.line})')
+		}
+		seq := c.check_expr(e.args[0])!
+		c.expect_struct_like(seq, 'keys()', e.line)!
+		return TypeInfo{ kind: .array_t }
+	}
+	if e.name == 'print' || e.name == 'println' {
+		if e.args.len != 1 {
+			return error('${e.name}() takes exactly one argument (line ${e.line})')
+		}
+		_ = c.check_expr(e.args[0])!
+		return TypeInfo{ kind: .unknown }
+	}
+	// host builtins (native) — validate arity from the spec table
+	bid, bargc := builtin_spec(e.name)
+	if bid >= 0 {
+		if e.args.len != bargc {
+			return error('${e.name}() takes exactly ${bargc} argument(s) (line ${e.line})')
+		}
+		for a in e.args {
+			_ = c.check_expr(a)!
+		}
+		return builtin_result_type(e.name)
+	}
+	// closure call: a local holding a function value
+	if e.name in c.types && c.types[e.name].kind == .closure_t {
+		for a in e.args {
+			_ = c.check_expr(a)!
+		}
+		return TypeInfo{ kind: .unknown }
+	}
+	// user function — arity is checked only when the signature is known.
+	// Unknown names are allowed: this toolchain supports separate compilation,
+	// so a call may resolve to a function in another object at link time.
+	// Truly missing functions are reported by the linker, not the checker.
+	if e.name in c.fns {
+		sig := c.fns[e.name]
+		// generic type arguments must match the declared type parameters
+		if e.type_args.len > 0 && e.type_args.len != sig.n_type_params {
+			return error('${e.name}() takes ${sig.n_type_params} type argument(s), got ${e.type_args.len} (line ${e.line})')
+		}
+		if e.type_args.len == 0 && sig.n_type_params > 0 {
+			// calling a generic function without explicit type args is fine —
+			// the VM infers from the values at runtime
+		}
+		if !sig.variadic {
+			if e.args.len < sig.min_args {
+				return error('${e.name}() expects at least ${sig.min_args} argument(s), got ${e.args.len} (line ${e.line})')
+			}
+			if e.args.len > sig.has_defs.len {
+				return error('${e.name}() expects at most ${sig.has_defs.len} argument(s), got ${e.args.len} (line ${e.line})')
+			}
+		}
+	}
+	for a in e.args {
+		_ = c.check_expr(a)!
+	}
+	return TypeInfo{ kind: .unknown }
+}
+
+fn builtin_result_type(name string) TypeInfo {
+	return match name {
+		'abs', 'min', 'max', 'floor', 'ceil', 'round', 'rand_int' { TypeInfo{ kind: .int_t } }
+		'pow', 'sqrt', 'rand', 'float', 'time' { TypeInfo{ kind: .float_t } }
+		'int' { TypeInfo{ kind: .int_t } }
+		'str', 'type', 'lower', 'upper', 'trim', 'getenv', 'read_file' { TypeInfo{ kind: .string_t } }
+		'contains', 'starts_with', 'ends_with' { TypeInfo{ kind: .bool_t } }
+		'split' { TypeInfo{ kind: .array_t } }
+		'join' { TypeInfo{ kind: .string_t } }
+		'sort', 'reverse' { TypeInfo{ kind: .array_t } }
+		'pop' { TypeInfo{ kind: .unknown } }
+		'clone', 'index_of' { TypeInfo{ kind: .unknown } }
+		'args', 'keys' { TypeInfo{ kind: .array_t } }
+		'len' { TypeInfo{ kind: .int_t } }
+		'write_file', 'setenv', 'exit', 'sleep', 'eprint' { TypeInfo{ kind: .unknown } }
+		else { TypeInfo{ kind: .unknown } }
+	}
+}
+
+fn is_num_kind(k CType) bool {
+	return k == .int_t || k == .float_t
+}
+
+fn type_name(k CType) string {
+	return match k {
+		.int_t { 'int' }
+		.float_t { 'float' }
+		.string_t { 'string' }
+		.bool_t { 'bool' }
+		.array_t { 'array' }
+		.struct_t { 'struct' }
+		.enum_t { 'enum' }
+		.closure_t { 'function' }
+		else { 'value' }
+	}
+}
+
+fn (mut c Checker) expect_numeric(t TypeInfo, what string, line int) ! {
+	if t.kind == .string_t || t.kind == .array_t || t.kind == .struct_t || t.kind == .bool_t || t.kind == .closure_t {
+		return error('${what} on a ${type_name(t.kind)} (line ${line})')
+	}
+}
+
+fn (mut c Checker) expect_int(t TypeInfo, what string, line int) ! {
+	if t.kind == .string_t || t.kind == .array_t || t.kind == .struct_t || t.kind == .bool_t || t.kind == .closure_t || t.kind == .float_t {
+		return error('${what} requires an int, got a ${type_name(t.kind)} (line ${line})')
+	}
+}
+
+fn (mut c Checker) expect_container(t TypeInfo, what string, line int) ! {
+	if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .closure_t {
+		return error('${what} on a ${type_name(t.kind)} (line ${line})')
+	}
+}
+
+fn (mut c Checker) expect_struct_like(t TypeInfo, what string, line int) ! {
+	if t.kind == .int_t || t.kind == .float_t || t.kind == .bool_t || t.kind == .string_t || t.kind == .closure_t {
+		return error('${what} on a ${type_name(t.kind)} (line ${line})')
+	}
+}
diff --git a/compiler/codegen.v b/compiler/codegen.v
index 6f33786..4653267 100644
--- a/compiler/codegen.v
+++ b/compiler/codegen.v
@@ -31,8 +31,10 @@ mut:
 	types     map[string]string      // local name -> declared struct type ('' = unknown)
 	structs   map[string][]string    // declared struct name -> field list
 	enums     map[string][]string    // enum name -> variant list
+	lam_counter int // anonymous function counter
 	enum_vals map[string]int         // 'Enum.variant' -> integer value
 	consts    map[string]i64         // constant name -> integer value
+	lines     []obj.LineInfo         // code offset -> source line (debug info)
 	local_cnt int
 	argc      int
 	cur_fn    string
@@ -78,7 +80,7 @@ fn gen(prog Program) !obj.Obj {
 	}
 	// compile imported files and merge their objects
 	for imp in prog.imports {
-		imported := compile_file(imp.path)!
+		imported := compile_file(resolve_import(imp.path)!)!
 		// merge symbols from the imported object
 		for s in imported.symbols {
 			g.symbols << s
@@ -93,6 +95,10 @@ fn gen(prog Program) !obj.Obj {
 		for r in imported.relocs {
 			g.relocs << obj.Reloc{ offset: u32(code_off) + r.offset, name: r.name, kind: r.kind }
 		}
+		// merge debug info, rebasing offsets into this object's code space
+		for l in imported.lines {
+			g.lines << obj.LineInfo{ off: u32(code_off) + l.off, line: l.line }
+		}
 	}
 	for fd in prog.fns {
 		g.gen_fn(fd)!
@@ -102,6 +108,7 @@ fn gen(prog Program) !obj.Obj {
 		strings: g.strings
 		code:    g.code
 		relocs:  g.relocs
+		lines:   g.lines
 	}
 }
 
@@ -111,6 +118,7 @@ fn (mut g Gen) gen_fn(fd FnDecl) ! {
 	sym := if fd.recv_type.len > 0 { '${fd.recv_type}.${fd.name}' } else { fd.name }
 	g.cur_fn = sym
 	g.symbols << obj.Symbol{ name: sym, entry: g.code.len }
+	g.lines << obj.LineInfo{ off: u32(g.code.len), line: fd.line }
 	g.locals.clear()
 	g.types.clear()
 	g.local_cnt = 0
@@ -121,20 +129,67 @@ fn (mut g Gen) gen_fn(fd FnDecl) ! {
 		g.types[fd.recv_name] = fd.recv_type
 		next = 1
 	}
+	// a variadic parameter does not occupy an argument slot; it gets a fresh
+	// local that the prologue fills with the collected vararg array
+	if fd.variadic {
+		g.argc--
+	}
 	for i, p in fd.params {
+		if fd.variadic && i == fd.params.len - 1 {
+			continue
+		}
 		g.locals[p] = i + next
 	}
 	g.local_cnt = g.argc
+	if fd.variadic {
+		vidx := g.local_cnt
+		g.local_cnt++
+		g.locals[fd.params[fd.params.len - 1]] = vidx
+	}
 	// `enter n` reserves the non-parameter locals; n is patched once the body
 	// has been scanned.
 	g.code << op_enter
 	g.enter_off = u32(g.code.len)
 	g.code << obj.encode_i64(0)
+	// default parameter values: if the caller passed fewer args than this
+	// param's slot, evaluate the default and store it
+	for i, p in fd.params {
+		if fd.variadic && i == fd.params.len - 1 {
+			continue
+		}
+		if i >= fd.has_defs.len || !fd.has_defs[i] {
+			continue
+		}
+		slot := i + next
+		skip_l := g.new_label()
+		g.code << op_argc
+		g.code << op_push_i
+		g.code << obj.encode_i64(i64(slot))
+		g.code << op_le
+		g.code << op_jz
+		g.code << obj.encode_i64(0)
+		g.fixups << Fixup{ name: skip_l, off: u32(g.code.len) - 8 }
+		g.gen_expr(fd.defaults[i])!
+		g.emit_store(slot)
+		g.emit_label(skip_l)
+	}
+	// variadic collection: build an array from args[argc..actual-1]
+	if fd.variadic {
+		vidx := g.locals[fd.params[fd.params.len - 1]] or {
+			return error('internal: variadic param missing')
+		}
+		g.code << op_varargs
+		g.code << obj.encode_i64(i64(g.argc))
+		g.code << obj.encode_i64(i64(vidx))
+	}
 	for st in fd.body {
 		g.gen_stmt(st)!
 	}
 	g.code << op_ret // trailing return for fall-through
-	obj.patch_i64(mut g.code, g.enter_off, i64(g.local_cnt - g.argc))
+	// reserve all local slots: the callee may be called with fewer arguments
+	// than declared (default parameters) or more (variadic), so the frame must
+	// always cover slots 0..local_cnt-1
+	obj.patch_i64(mut g.code, g.enter_off, i64(g.local_cnt))
 	// resolve intra-function jump targets
 	for f in g.fixups {
 		target := g.labels[f.name] or {
@@ -148,6 +203,7 @@ fn (mut g Gen) gen_fn(fd FnDecl) ! {
 }
 
 fn (mut g Gen) gen_stmt(st Stmt) ! {
+	g.lines << obj.LineInfo{ off: u32(g.code.len), line: st.line }
 	match st.kind {
 		.expr_stmt {
 			g.gen_expr(st.expr)!
@@ -168,6 +224,28 @@ fn (mut g Gen) gen_stmt(st Stmt) ! {
 			g.code << op_store
 			g.code << obj.encode_i64(i64(idx))
 		}
+		.destruct_stmt {
+			// let { a, b } = e  →  tmp := e; a := tmp.a; b := tmp.b
+			// let [a, b] = e   →  tmp := e; a := tmp[0]; b := tmp[1]
+			tmp_idx := g.new_local()
+			g.gen_expr(st.expr)!
+			g.emit_store(tmp_idx)
+			for i, name in st.destruct_targets {
+				g.emit_load(tmp_idx)
+				if st.destruct_field {
+					g.emit_field_name(name)
+					g.code << op_sget
+				} else {
+					g.code << op_push_i
+					g.code << obj.encode_i64(i64(i))
+					g.code << op_aget
+				}
+				idx := g.new_local()
+				g.locals[name] = idx
+				g.types.delete(name)
+				g.emit_store(idx)
+			}
+		}
 		.assign_stmt {
 			idx := g.locals[st.target] or {
 				return error('unknown variable "${st.target}" at line ${st.line}')
@@ -350,9 +428,26 @@ fn (mut g Gen) gen_stmt(st Stmt) ! {
 			prev_t := g.types[st.target] or { '' }
 			g.locals[st.target] = elem_idx
 			g.types.delete(st.target)
+			// bind the index variable if present (for i, v in arr)
+			prev_idx := if st.idx_target.len > 0 { g.locals[st.idx_target] or { -1 } } else { -1 }
+			prev_idx_t := if st.idx_target.len > 0 { g.types[st.idx_target] or { '' } } else { '' }
+			if st.idx_target.len > 0 {
+				g.locals[st.idx_target] = idx_idx
+				g.types.delete(st.idx_target)
+			}
 			for s in st.body {
 				g.gen_stmt(s)!
 			}
+			if st.idx_target.len > 0 {
+				if prev_idx >= 0 {
+					g.locals[st.idx_target] = prev_idx
+				} else {
+					g.locals.delete(st.idx_target)
+				}
+				if prev_idx_t.len > 0 {
+					g.types[st.idx_target] = prev_idx_t
+				}
+			}
 			if prev >= 0 {
 				g.locals[st.target] = prev
 			} else {
@@ -403,6 +498,44 @@ fn (mut g Gen) gen_stmt(st Stmt) ! {
 			g.code << obj.encode_i64(0)
 			g.fixups << Fixup{ name: ctx.continue_l, off: u32(g.code.len) - 8 }
 		}
+		.throw_stmt {
+			g.gen_expr(st.expr)!
+			g.code << op_throw
+		}
+		.try_stmt {
+			catch_l := g.new_label()
+			end_l := g.new_label()
+			err_idx := g.new_local()
+			g.code << op_try
+			g.code << obj.encode_i64(0)
+			g.fixups << Fixup{ name: catch_l, off: u32(g.code.len) - 8 }
+			for s in st.body {
+				g.gen_stmt(s)!
+			}
+			g.code << op_catch_done
+			g.code << op_jmp
+			g.code << obj.encode_i64(0)
+			g.fixups << Fixup{ name: end_l, off: u32(g.code.len) - 8 }
+			g.emit_label(catch_l)
+			g.code << op_store
+			g.code << obj.encode_i64(i64(err_idx))
+			prev := g.locals[st.target] or { -1 }
+			prev_t := g.types[st.target] or { '' }
+			g.locals[st.target] = err_idx
+			g.types.delete(st.target)
+			for s in st.els {
+				g.gen_stmt(s)!
+			}
+			if prev >= 0 {
+				g.locals[st.target] = prev
+			} else {
+				g.locals.delete(st.target)
+			}
+			if prev_t.len > 0 {
+				g.types[st.target] = prev_t
+			}
+			g.emit_label(end_l)
+		}
 	}
 }
 
@@ -412,6 +545,10 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 			g.code << op_push_i
 			g.code << obj.encode_i64(e.int_v)
 		}
+		.float_lit {
+			g.code << op_push_f
+			g.code << obj.encode_f64(e.float_v)
+		}
 		.str_lit {
 			// the index is a placeholder; the linker rebases it via a string
 			// relocation so multi-file links keep working
@@ -468,7 +605,21 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 		}
 		.method_call {
 			// p.dist(x)  →  call <Type>.dist  p, x
-			recv_t := g.method_receiver_type(e)!
+			recv_t := g.method_receiver_type(e)
+			// string methods: s.len(), s.to_upper(), s.contains(x), ... —
+			// the receiver type is known when it is a literal or a local that
+			// was assigned a string literal
+			if recv_t == 'string' || e.left.kind == .str_lit {
+				g.gen_expr(*e.left)!
+				for a in e.args {
+					g.gen_expr(a)!
+				}
+				g.code << op_str_method
+				g.code << obj.encode_i64(0) // name placeholder — rebased by the linker
+				g.relocs << obj.Reloc{ offset: u32(g.code.len) - 8, name: e.name, kind: 1 }
+				g.code << obj.encode_i64(i64(e.args.len))
+				return
+			}
 			// built-in: enum.to_string() generates a match on the integer value
 			if e.name == 'to_string' && recv_t in g.enums && e.args.len == 0 {
 				g.gen_enum_to_string(recv_t, *e.left, e.line)!
@@ -487,11 +638,24 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 			for a in e.args {
 				g.gen_expr(a)!
 			}
-			g.code << op_call
-			g.code << obj.encode_i64(0) // placeholder — patched by the linker
-			g.relocs << obj.Reloc{ offset: u32(g.code.len) - 8, name: '${recv_t}.${e.name}', kind: 0 }
-			g.code << obj.encode_i64(i64(e.args.len + 1)) // receiver + args
+			// if receiver type is known, emit a static method call
+			if recv_t.len > 0 {
+				g.code << op_call
+				g.code << obj.encode_i64(0) // placeholder — patched by the linker
+				g.relocs << obj.Reloc{ offset: u32(g.code.len) - 8, name: '${recv_t}.${e.name}', kind: 0 }
+				g.code << obj.encode_i64(i64(e.args.len + 1)) // receiver + args
+		} else {
+			// unknown type: treat as closure call on a struct field
+			g.emit_field_name(e.name)
+			g.code << op_sget
+			for a in e.args {
+				g.gen_expr(a)!
+			}
+			g.code << op_call_closure
+			g.code << obj.encode_i64(i64(e.args.len))
 		}
+		return
+	}
 		.index {
 			// if the index is a string literal, use struct field access (map style)
 			if e.right.kind == .str_lit {
@@ -504,6 +668,57 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 				g.code << op_aget
 			}
 		}
+		.slice {
+			// arr[start..end]  →  push value, start, end; slice
+			g.gen_expr(*e.left)!
+			g.gen_expr(*e.right)!
+			g.gen_expr(*e.extra)!
+			g.code << op_slice
+		}
+		.anon_fn {
+			g.lam_counter++
+			name := '__lam_${g.lam_counter}'
+			// jump over the lambda body so callers don't fall through
+			g.code << op_jmp
+			g.code << obj.encode_i64(0)
+			skip_fix_off := u32(g.code.len) - 8
+			fd := FnDecl{
+				name: name
+				params: e.fparams
+				defaults: e.fdefaults
+				has_defs: e.fhas_defs
+				variadic: e.fvariadic
+				body: e.fn_body
+				line: e.line
+			}
+			// Save enclosing fixup/label/locals/type state; gen_fn clears them.
+			// enter_off and argc are also per-function, so they must be restored
+			// or the enclosing function's `enter n` patch is lost (locals would
+			// then collide with the stack top).
+			saved_fixups := g.fixups.clone()
+			saved_labels := g.labels.clone()
+			saved_locals := g.locals.clone()
+			saved_types := g.types.clone()
+			saved_local_cnt := g.local_cnt
+			saved_enter_off := g.enter_off
+			saved_argc := g.argc
+			g.labels.clear()
+			g.fixups = []Fixup{}
+			g.gen_fn(fd)!
+			// Restore the enclosing state.
+			g.fixups = saved_fixups
+			g.labels = saved_labels.clone()
+			g.locals = saved_locals.clone()
+			g.types = saved_types.clone()
+			g.local_cnt = saved_local_cnt
+			g.enter_off = saved_enter_off
+			g.argc = saved_argc
+			// Patch the skip jump to land at the closure opcode we emit next.
+			obj.patch_i64(mut g.code, skip_fix_off, i64(g.code.len))
+			g.code << op_closure
+			g.code << obj.encode_i64(0)
+			g.relocs << obj.Reloc{ offset: u32(g.code.len) - 8, name: name, kind: 0 }
+		}
 		.bool_lit {
 			g.code << op_push_i
 			g.code << obj.encode_i64(e.int_v)
@@ -526,11 +741,29 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 			}
 		}
 		.unary {
+			// constant-fold unary ops on literals: -5, -2.5, not true, ~7
+			if e.right.kind == .int_lit && (e.op == .minus || e.op == .tilde) {
+				v := e.right.int_v
+				res := if e.op == .minus { -v } else { ~v }
+				g.code << op_push_i
+				g.code << obj.encode_i64(res)
+				return
+			}
+			if e.right.kind == .float_lit && e.op == .minus {
+				g.code << op_push_f
+				g.code << obj.encode_f64(-e.right.float_v)
+				return
+			}
+			if e.right.kind == .bool_lit && e.op == .kw_not {
+				g.code << op_push_i
+				g.code << obj.encode_i64(if e.right.int_v == 0 { 1 } else { 0 })
+				return
+			}
 			g.gen_expr(*e.right)!
-			if e.op == .kw_not {
-				g.code << op_not
-			} else {
-				g.code << op_neg
+			match e.op {
+				.kw_not { g.code << op_not }
+				.tilde { g.code << op_not_b }
+				else { g.code << op_neg }
 			}
 		}
 		.binary {
@@ -594,6 +827,31 @@ fn (mut g Gen) gen_call(e Expr) ! {
 		g.code << op_skeys
 		return
 	}
+	// closure call: ident(args) where ident is a local holding a closure
+	if e.name in g.locals {
+		g.gen_expr(Expr{ kind: .ident, name: e.name, line: e.line })!
+		g.code << op_dup  // separate the closure copy from the local slot
+		for a in e.args {
+			g.gen_expr(a)!
+		}
+		g.code << op_call_closure
+		g.code << obj.encode_i64(i64(e.args.len))
+		return
+	}
+	// host builtins (file I/O, OS, math, collections) go through op_native
+	bid, bargc := builtin_spec(e.name)
+	if bid >= 0 {
+		if e.args.len != bargc {
+			return error('${e.name}() takes exactly ${bargc} argument(s) (line ${e.line})')
+		}
+		for a in e.args {
+			g.gen_expr(a)!
+		}
+		g.code << op_native
+		g.code << obj.encode_i64(i64(bid))
+		g.code << obj.encode_i64(i64(bargc))
+		return
+	}
 	for a in e.args {
 		g.gen_expr(a)!
 	}
@@ -603,7 +861,169 @@ fn (mut g Gen) gen_call(e Expr) ! {
 	g.code << obj.encode_i64(i64(e.args.len)) // argc
 }
 
+// builtin_spec maps a builtin function name to its (native id, arg count).
+// A negative id means the name is not a builtin (it is a user function).
+fn builtin_spec(name string) (int, int) {
+	return match name {
+		'abs' { native_abs, 1 }
+		'min' { native_min, 2 }
+		'max' { native_max, 2 }
+		'pow' { native_pow, 2 }
+		'sqrt' { native_sqrt, 1 }
+		'floor' { native_floor, 1 }
+		'ceil' { native_ceil, 1 }
+		'round' { native_round, 1 }
+		'rand' { native_rand, 0 }
+		'rand_int' { native_rand_int, 1 }
+		'int' { native_int, 1 }
+		'str' { native_str, 1 }
+		'float' { native_float, 1 }
+		'type' { native_type, 1 }
+		'split' { native_split, 2 }
+		'join' { native_join, 2 }
+		'contains' { native_contains, 2 }
+		'starts_with' { native_starts_with, 2 }
+		'ends_with' { native_ends_with, 2 }
+		'trim' { native_trim, 1 }
+		'lower' { native_lower, 1 }
+		'upper' { native_upper, 1 }
+		'pop' { native_pop, 1 }
+		'insert' { native_insert, 3 }
+		'remove' { native_remove, 2 }
+		'sort' { native_sort, 1 }
+		'clone' { native_clone, 1 }
+		'reverse' { native_reverse, 1 }
+		'index_of' { native_index_of, 2 }
+		'args' { native_args, 0 }
+		'getenv' { native_getenv, 1 }
+		'setenv' { native_setenv, 2 }
+		'exit' { native_exit, 1 }
+		'time' { native_time, 0 }
+		'sleep' { native_sleep, 1 }
+		'read_file' { native_read_file, 1 }
+		'write_file' { native_write_file, 2 }
+		'eprint' { native_eprint, 1 }
+		else { -1, 0 }
+	}
+}
+
+// fold_binary constant-folds binary expressions whose operands are both
+// literals, emitting the precomputed constant. Returns false when the
+// expression cannot be folded (leaving it to the runtime). Division/modulo by
+// zero and out-of-range shifts are deliberately not folded so the runtime
+// still reports them.
+fn (mut g Gen) fold_binary(e Expr) bool {
+	// integer folding
+	if e.left.kind == .int_lit && e.right.kind == .int_lit {
+		l := e.left.int_v
+		r := e.right.int_v
+		mut res := i64(0)
+		match e.op {
+			.plus { res = l + r }
+			.minus { res = l - r }
+			.star { res = l * r }
+			.slash {
+				if r == 0 {
+					return false
+				}
+				res = l / r
+			}
+			.percent {
+				if r == 0 {
+					return false
+				}
+				res = l % r
+			}
+			.amp { res = l & r }
+			.pipe { res = l | r }
+			.caret { res = l ^ r }
+			.lt_lt {
+				if r < 0 || r > 63 {
+					return false
+				}
+				res = l << u32(r)
+			}
+			.gt_gt {
+				if r < 0 || r > 63 {
+					return false
+				}
+				res = l >> u32(r)
+			}
+			.eq_eq { res = if l == r { 1 } else { 0 } }
+			.not_eq { res = if l != r { 1 } else { 0 } }
+			.lt { res = if l < r { 1 } else { 0 } }
+			.le { res = if l <= r { 1 } else { 0 } }
+			.gt { res = if l > r { 1 } else { 0 } }
+			.ge { res = if l >= r { 1 } else { 0 } }
+			else { return false }
+		}
+		g.code << op_push_i
+		g.code << obj.encode_i64(res)
+		return true
+	}
+	// float folding
+	if e.left.kind == .float_lit && e.right.kind == .float_lit {
+		l := e.left.float_v
+		r := e.right.float_v
+		mut res := 0.0
+		mut is_bool := false
+		mut bres := false
+		match e.op {
+			.plus { res = l + r }
+			.minus { res = l - r }
+			.star { res = l * r }
+			.slash {
+				if r == 0.0 {
+					return false
+				}
+				res = l / r
+			}
+			.eq_eq { is_bool = true; bres = l == r }
+			.not_eq { is_bool = true; bres = l != r }
+			.lt { is_bool = true; bres = l < r }
+			.le { is_bool = true; bres = l <= r }
+			.gt { is_bool = true; bres = l > r }
+			.ge { is_bool = true; bres = l >= r }
+			else { return false }
+		}
+		if is_bool {
+			g.code << op_push_i
+			g.code << obj.encode_i64(if bres { 1 } else { 0 })
+		} else {
+			g.code << op_push_f
+			g.code << obj.encode_f64(res)
+		}
+		return true
+	}
+	// string concatenation folding: "a" + "b" → one interned constant.
+	// The string is emitted as a relocation so the linker interns it in the
+	// final table, exactly like a plain string literal.
+	if e.left.kind == .str_lit && e.right.kind == .str_lit && e.op == .plus {
+		g.code << op_push_s
+		g.code << obj.encode_i64(0) // placeholder — rebased by the linker
+		g.relocs << obj.Reloc{ offset: u32(g.code.len) - 8, name: e.left.str_v + e.right.str_v, kind: 1 }
+		return true
+	}
+	// boolean short-circuit folding: only when both sides are bool literals
+	if e.left.kind == .bool_lit && e.right.kind == .bool_lit {
+		if e.op == .kw_and {
+			g.code << op_push_i
+			g.code << obj.encode_i64(if e.left.int_v != 0 && e.right.int_v != 0 { 1 } else { 0 })
+			return true
+		}
+		if e.op == .kw_or {
+			g.code << op_push_i
+			g.code << obj.encode_i64(if e.left.int_v != 0 || e.right.int_v != 0 { 1 } else { 0 })
+			return true
+		}
+	}
+	return false
+}
+
 fn (mut g Gen) gen_binary(e Expr) ! {
+	if g.fold_binary(e) {
+		return
+	}
 	match e.op {
 		.kw_and {
 			// a and b  →  short-circuit: if !a or !b then 0 else 1
@@ -664,6 +1084,11 @@ fn (mut g Gen) gen_binary(e Expr) ! {
 				.le { op_le }
 				.gt { op_gt }
 				.ge { op_ge }
+				.amp { op_and_b }
+				.pipe { op_or_b }
+				.caret { op_xor }
+				.lt_lt { op_shl }
+				.gt_gt { op_shr }
 				else {
 					return error('unsupported binary operator at line ${e.line}')
 				}
@@ -678,6 +1103,9 @@ fn (mut g Gen) gen_binary(e Expr) ! {
 // variable, or an enum variant `Enum.variant`. Everything else has no
 // known type ('').
 fn (mut g Gen) expr_type(e Expr) string {
+	if e.kind == .str_lit {
+		return 'string'
+	}
 	if e.kind == .struct_lit {
 		return e.name
 	}
@@ -691,14 +1119,28 @@ fn (mut g Gen) expr_type(e Expr) string {
 			return e.left.name
 		}
 	}
+	// slicing or indexing a known string yields a string
+	if (e.kind == .slice || e.kind == .index) && g.expr_type(*e.left) == 'string' {
+		return 'string'
+	}
+	// string concatenation: "a" + "b" (or anything + a string literal)
+	if e.kind == .binary && e.op == .plus && (e.left.kind == .str_lit || e.right.kind == .str_lit) {
+		return 'string'
+	}
+	// string-producing builtins typed as strings so method chains keep working
+	if e.kind == .call {
+		return match e.name {
+			'upper', 'lower', 'trim', 'str', 'getenv', 'read_file', 'join' { 'string' }
+			else { '' }
+		}
+	}
 	return ''
 }
 
 // method_receiver_type resolves the struct type a method call is made on.
-// The receiver must be a plain variable whose type the compiler knows
-// (from a typed literal, an assignment, or a method receiver binding)
-// or an enum variant expression (e.g. Color.red).
-fn (mut g Gen) method_receiver_type(e Expr) !string {
+// Returns '' when the type is statically unknown (at which point the
+// call becomes a dynamic closure invocation via field access).
+fn (mut g Gen) method_receiver_type(e Expr) string {
 	recv := e.left
 	if recv.kind == .ident {
 		t := g.types[recv.name] or { '' }
@@ -706,14 +1148,14 @@ fn (mut g Gen) method_receiver_type(e Expr) !string {
 			return t
 		}
 	}
-	// enum variant: Color.red  →  type is "Color"
+	// enum variant: Color.red  ->  type is "Color"
 	if recv.kind == .field && recv.left.kind == .ident {
 		key := '${recv.left.name}.${recv.name}'
 		if key in g.enum_vals {
 			return recv.left.name
 		}
 	}
-	return error('cannot resolve method "${e.name}": receiver type unknown (line ${e.line})')
+	return ''
 }
 
 // gen_enum_to_string generates bytecode for `e.to_string()` on an enum value.
diff --git a/compiler/compiler.v b/compiler/compiler.v
index 429cd70..e1db6f0 100644
--- a/compiler/compiler.v
+++ b/compiler/compiler.v
@@ -8,6 +8,8 @@ import obj
 pub fn compile(src string) !obj.Obj {
 	toks := tokenize(src)!
 	prog := parse(toks)!
+	// conservative compile-time type check; catches provable errors early
+	check(prog)!
 	return gen(prog)
 }
 
@@ -15,3 +17,18 @@ pub fn compile_file(path string) !obj.Obj {
 	src := os.read_file(path)!
 	return compile(src)!
 }
+
+// resolve_import turns an import path into a readable source file. It tries
+// the path as given first, then falls back to the package-manager layout so
+// `import "pkg/file.vr"` finds vendor/pkg/file.vr.
+pub fn resolve_import(path string) !string {
+	if os.exists(path) {
+		return path
+	}
+	for cand in ['vendor/${path}', 'vendor/${path}.vr', 'vendor/${path}/main.vr', 'vendor/${path}/src/main.vr'] {
+		if os.exists(cand) {
+			return cand
+		}
+	}
+	return error('cannot resolve import "${path}" (tried vendor/)"')
+}
diff --git a/compiler/lexer.v b/compiler/lexer.v
index 9b9820f..330356b 100644
--- a/compiler/lexer.v
+++ b/compiler/lexer.v
@@ -2,7 +2,7 @@
 module compiler
 
 pub fn tokenize(src string) ![]Tok {
-	mut l := Lexer{ src: src }
+	mut l := Lexer{ src: src, line: 1 }
 	mut toks := []Tok{}
 	for {
 		t := l.next()!
@@ -16,9 +16,10 @@ pub fn tokenize(src string) ![]Tok {
 
 struct Lexer {
 mut:
-	src  string
-	pos  int
-	line int
+	src        string
+	pos        int
+	line       int
+	line_start int // byte offset where the current line begins
 }
 
 fn (mut l Lexer) peek() u8 {
@@ -40,6 +41,7 @@ fn (mut l Lexer) advance() u8 {
 	l.pos++
 	if c == `\n` {
 		l.line++
+		l.line_start = l.pos
 	}
 	return c
 }
@@ -61,34 +63,35 @@ fn (mut l Lexer) next() !Tok {
 		break
 	}
 	line := l.line
+	col := l.pos - l.line_start + 1 // 1-based column
 	if l.pos >= l.src.len {
-		return Tok{ kind: .eof, lit: '', line: line }
+		return Tok{ kind: .eof, lit: '', line: line, col: col }
 	}
 	c := l.peek()
 	match c {
 		`(` {
 			l.advance()
-			return Tok{ kind: .lparen, lit: '(', line: line }
+			return Tok{ kind: .lparen, lit: '(', line: line, col: col }
 		}
 		`)` {
 			l.advance()
-			return Tok{ kind: .rparen, lit: ')', line: line }
+			return Tok{ kind: .rparen, lit: ')', line: line, col: col }
 		}
 		`{` {
 			l.advance()
-			return Tok{ kind: .lbrace, lit: '{', line: line }
+			return Tok{ kind: .lbrace, lit: '{', line: line, col: col }
 		}
 		`}` {
 			l.advance()
-			return Tok{ kind: .rbrace, lit: '}', line: line }
+			return Tok{ kind: .rbrace, lit: '}', line: line, col: col }
 		}
 		`[` {
 			l.advance()
-			return Tok{ kind: .lbracket, lit: '[', line: line }
+			return Tok{ kind: .lbracket, lit: '[', line: line, col: col }
 		}
 		`]` {
 			l.advance()
-			return Tok{ kind: .rbracket, lit: ']', line: line }
+			return Tok{ kind: .rbracket, lit: ']', line: line, col: col }
 		}
 		`.` {
 			l.advance()
@@ -96,112 +99,165 @@ fn (mut l Lexer) next() !Tok {
 				l.advance()
 				if l.peek() == `.` {
 					l.advance()
-					return Tok{ kind: .dotdotdot, lit: '...', line: line }
+					return Tok{ kind: .dotdotdot, lit: '...', line: line, col: col }
 				}
-				return Tok{ kind: .dotdot, lit: '..', line: line }
+				return Tok{ kind: .dotdot, lit: '..', line: line, col: col }
 			}
-			return Tok{ kind: .dot, lit: '.', line: line }
+			return Tok{ kind: .dot, lit: '.', line: line, col: col }
 		}
 		`,` {
 			l.advance()
-			return Tok{ kind: .comma, lit: ',', line: line }
+			return Tok{ kind: .comma, lit: ',', line: line, col: col }
 		}
 		`:` {
 			l.advance()
-			return Tok{ kind: .colon, lit: ':', line: line }
+			return Tok{ kind: .colon, lit: ':', line: line, col: col }
 		}
 		`+` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .plus_eq, lit: '+=', line: line }
+				return Tok{ kind: .plus_eq, lit: '+=', line: line, col: col }
 			}
-			return Tok{ kind: .plus, lit: '+', line: line }
+			return Tok{ kind: .plus, lit: '+', line: line, col: col }
 		}
 		`-` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .minus_eq, lit: '-=', line: line }
+				return Tok{ kind: .minus_eq, lit: '-=', line: line, col: col }
 			}
-			return Tok{ kind: .minus, lit: '-', line: line }
+			return Tok{ kind: .minus, lit: '-', line: line, col: col }
 		}
 		`*` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .star_eq, lit: '*=', line: line }
+				return Tok{ kind: .star_eq, lit: '*=', line: line, col: col }
 			}
-			return Tok{ kind: .star, lit: '*', line: line }
+			return Tok{ kind: .star, lit: '*', line: line, col: col }
 		}
 		`/` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .slash_eq, lit: '/=', line: line }
+				return Tok{ kind: .slash_eq, lit: '/=', line: line, col: col }
 			}
-			return Tok{ kind: .slash, lit: '/', line: line }
+			return Tok{ kind: .slash, lit: '/', line: line, col: col }
 		}
 		`%` {
 			l.advance()
-			return Tok{ kind: .percent, lit: '%', line: line }
+			return Tok{ kind: .percent, lit: '%', line: line, col: col }
+		}
+		`&` {
+			l.advance()
+			return Tok{ kind: .amp, lit: '&', line: line, col: col }
+		}
+		`|` {
+			l.advance()
+			return Tok{ kind: .pipe, lit: '|', line: line, col: col }
+		}
+		`^` {
+			l.advance()
+			return Tok{ kind: .caret, lit: '^', line: line, col: col }
+		}
+		`~` {
+			l.advance()
+			return Tok{ kind: .tilde, lit: '~', line: line, col: col }
 		}
 		`=` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .eq_eq, lit: '==', line: line }
+				return Tok{ kind: .eq_eq, lit: '==', line: line, col: col }
 			}
-			return Tok{ kind: .assign, lit: '=', line: line }
+			return Tok{ kind: .assign, lit: '=', line: line, col: col }
 		}
 		`!` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .not_eq, lit: '!=', line: line }
+				return Tok{ kind: .not_eq, lit: '!=', line: line, col: col }
 			}
-			return error('unexpected character "!" at line ${line} (did you mean "not"?)')
+			return error('unexpected character "!" at line ${line}, col ${col} (did you mean "not"?)')
 		}
 		`<` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .le, lit: '<=', line: line }
+				return Tok{ kind: .le, lit: '<=', line: line, col: col }
 			}
-			return Tok{ kind: .lt, lit: '<', line: line }
+			if l.peek() == `<` {
+				l.advance()
+				return Tok{ kind: .lt_lt, lit: '<<', line: line, col: col }
+			}
+			return Tok{ kind: .lt, lit: '<', line: line, col: col }
 		}
 		`>` {
 			l.advance()
 			if l.peek() == `=` {
 				l.advance()
-				return Tok{ kind: .ge, lit: '>=', line: line }
+				return Tok{ kind: .ge, lit: '>=', line: line, col: col }
 			}
-			return Tok{ kind: .gt, lit: '>', line: line }
+			if l.peek() == `>` {
+				l.advance()
+				return Tok{ kind: .gt_gt, lit: '>>', line: line, col: col }
+			}
+			return Tok{ kind: .gt, lit: '>', line: line, col: col }
 		}
 		`\"` {
-			return l.lex_string(line)!
+			return l.lex_string(line, col)!
 		}
 		`0`...`9` {
-			return l.lex_number(line)
+			return l.lex_number(line, col)
 		}
 		else {
 			if (c >= `a` && c <= `z`) || (c >= `A` && c <= `Z`) || c == `_` {
-				return l.lex_ident(line)
+				return l.lex_ident(line, col)
 			}
-			return error('unexpected character "${c.ascii_str()}" at line ${line}')
+			return error('unexpected character "${c.ascii_str()}" at line ${line}, col ${col}')
 		}
 	}
 }
 
-fn (mut l Lexer) lex_number(line int) Tok {
+fn (mut l Lexer) lex_number(line int, col int) Tok {
 	start := l.pos
 	for l.pos < l.src.len && l.peek() >= `0` && l.peek() <= `9` {
 		l.advance()
 	}
-	return Tok{ kind: .int_lit, lit: l.src[start..l.pos], line: line }
+	mut is_float := false
+	// fractional part: `.` followed by a digit (so `1..3` and `1...3` stay ints)
+	if l.peek() == `.` && l.pos + 1 < l.src.len && l.peek2() >= `0` && l.peek2() <= `9` {
+		is_float = true
+		l.advance() // consume `.`
+		for l.pos < l.src.len && l.peek() >= `0` && l.peek() <= `9` {
+			l.advance()
+		}
+	}
+	// exponent part: e / E followed by optional sign and digits
+	if l.peek() == `e` || l.peek() == `E` {
+		save := l.pos
+		l.advance()
+		if l.peek() == `+` || l.peek() == `-` {
+			l.advance()
+		}
+		if l.peek() >= `0` && l.peek() <= `9` {
+			is_float = true
+			for l.pos < l.src.len && l.peek() >= `0` && l.peek() <= `9` {
+				l.advance()
+			}
+		} else {
+			l.pos = save // not an exponent after all
+		}
+	}
+	lit := l.src[start..l.pos]
+	if is_float {
+		return Tok{ kind: .float_lit, lit: lit, line: line, col: col }
+	}
+	return Tok{ kind: .int_lit, lit: lit, line: line, col: col }
 }
 
-fn (mut l Lexer) lex_ident(line int) Tok {
+fn (mut l Lexer) lex_ident(line int, col int) Tok {
 	start := l.pos
 	for l.pos < l.src.len {
 		c := l.peek()
@@ -236,18 +292,26 @@ fn (mut l Lexer) lex_ident(line int) Tok {
 		'import' { TokKind.kw_import }
 		'enum' { TokKind.kw_enum }
 		'const' { TokKind.kw_const }
+		'interface' { TokKind.kw_interface }
+		'try' { TokKind.kw_try }
+		'catch' { TokKind.kw_catch }
+		'throw' { TokKind.kw_throw }
 		else { TokKind.ident }
 	}
-	return Tok{ kind: kind, lit: lit, line: line }
+	return Tok{ kind: kind, lit: lit, line: line, col: col }
 }
 
-fn (mut l Lexer) lex_string(line int) !Tok {
+fn (mut l Lexer) lex_string(line int, col int) !Tok {
 	l.advance() // opening quote
 	mut s := ''
+	mut has_interp := false
 	for l.pos < l.src.len {
 		c := l.advance()
 		if c == `\"` {
-			return Tok{ kind: .str_lit, lit: s, line: line }
+			if has_interp {
+				return Tok{ kind: .str_interp, lit: s, line: line, col: col }
+			}
+			return Tok{ kind: .str_lit, lit: s, line: line, col: col }
 		}
 		if c == `\\` {
 			if l.pos >= l.src.len {
@@ -268,12 +332,18 @@ fn (mut l Lexer) lex_string(line int) !Tok {
 					s += '\\'
 				}
 				else {
-					return error('invalid escape \\${e.ascii_str()} at line ${line}')
+					return error('invalid escape \\${e.ascii_str()} at line ${line}, col ${col}')
 				}
 			}
 			continue
 		}
+		if c == `$` && l.peek() == `{` {
+			has_interp = true
+			s += '\${'
+			l.advance() // skip the '{'
+			continue
+		}
 		s += c.ascii_str()
 	}
-	return error('unterminated string at line ${line}')
+	return error('unterminated string at line ${line}, col ${col}')
 }
diff --git a/compiler/opcodes.v b/compiler/opcodes.v
index 73ac572..c30d491 100644
--- a/compiler/opcodes.v
+++ b/compiler/opcodes.v
@@ -47,3 +47,61 @@ const op_shas = u8(40)
 const op_sdel = u8(41)
 const op_slen = u8(42)
 const op_skeys = u8(43)
+const op_slice = u8(44)
+const op_push_f = u8(45)
+const op_native = u8(46)
+const op_and_b = u8(47)
+const op_or_b = u8(48)
+const op_xor = u8(49)
+const op_shl = u8(50)
+const op_shr = u8(51)
+const op_not_b = u8(52)
+const op_try = u8(53)
+const op_throw = u8(54)
+const op_catch_done = u8(55)
+const op_closure = u8(56)
+const op_call_closure = u8(57)
+const op_argc = u8(58) // push the current frame's arg count
+const op_load_dyn = u8(59) // pop idx, push stack[bp + idx]
+const op_varargs = u8(60) // <named:i64> <dst:i64> — collect args[named..argc-1] into an array at local dst
+const op_str_method = u8(61) // <name:str> <argc:i64> — call a string method (s.len(), s.contains(x), ...)
+
+// native builtin ids (keep in sync with vm/opcodes.v)
+const native_abs = 100
+const native_min = 101
+const native_max = 102
+const native_pow = 103
+const native_sqrt = 104
+const native_floor = 105
+const native_ceil = 106
+const native_round = 107
+const native_rand = 108
+const native_rand_int = 109
+const native_int = 110
+const native_str = 111
+const native_float = 112
+const native_type = 113
+const native_split = 114
+const native_join = 115
+const native_contains = 116
+const native_starts_with = 117
+const native_ends_with = 118
+const native_trim = 119
+const native_lower = 120
+const native_upper = 121
+const native_pop = 122
+const native_insert = 123
+const native_remove = 124
+const native_sort = 125
+const native_clone = 126
+const native_reverse = 127
+const native_index_of = 128
+const native_args = 129
+const native_getenv = 130
+const native_setenv = 131
+const native_exit = 132
+const native_time = 133
+const native_sleep = 134
+const native_read_file = 135
+const native_write_file = 136
+const native_eprint = 137
diff --git a/compiler/parser.v b/compiler/parser.v
index 29ec861..f99984e 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -64,7 +64,7 @@ fn (mut p Parser) advance() Tok {
 fn (mut p Parser) expect(k TokKind, what string) !Tok {
 	t := p.cur()
 	if t.kind != k {
-		return error('expected ${what}, got "${t.lit}" at line ${t.line}')
+		return error('expected ${what}, got "${t.lit}" at line ${t.line}, col ${t.col}')
 	}
 	return p.advance()
 }
@@ -92,8 +92,9 @@ fn (mut p Parser) parse_program() !Program {
 			.kw_struct { prog.structs << p.parse_struct_decl()! }
 			.kw_enum { prog.enums << p.parse_enum_decl()! }
 			.kw_const { prog.consts << p.parse_const_decl()! }
+			.kw_interface { prog.interfaces << p.parse_interface_decl()! }
 			.kw_fn { prog.fns << p.parse_fn()! }
-			else { return error('unexpected token "${p.cur().lit}" at line ${p.cur().line}') }
+			else { return error('unexpected token "${p.cur().lit}" at line ${p.cur().line}, col ${p.cur().col}') }
 		}
 	}
 	if prog.fns.len == 0 {
@@ -163,6 +164,42 @@ fn (mut p Parser) parse_const_decl() !ConstDecl {
 	return ConstDecl{ name: name.lit, value: value, line: t.line }
 }
 
+// parse_interface_decl parses `interface Name { method1() method2() ... }`.
+// Methods may optionally be followed by `()` (any parameter list is ignored)
+// and are separated by commas or newlines.
+fn (mut p Parser) parse_interface_decl() !InterfaceDecl {
+	t := p.expect(.kw_interface, "'interface'")!
+	name := p.expect(.ident, 'interface name')!
+	p.expect(.lbrace, "'{'")!
+	mut methods := []InterfaceMethod{}
+	if p.cur().kind != .rbrace {
+		for {
+			mname := p.expect(.ident, 'method name')!
+			if p.cur().kind == .lparen {
+				p.advance()
+				for p.cur().kind != .rparen {
+					if p.cur().kind == .eof {
+						return error('unexpected end of file in interface method (line ${mname.line})')
+					}
+					p.advance()
+				}
+				p.expect(.rparen, "')'")!
+			}
+			methods << InterfaceMethod{ name: mname.lit, line: mname.line }
+			if p.cur().kind == .comma {
+				p.advance()
+				continue
+			}
+			if p.cur().kind != .rbrace {
+				continue
+			}
+			break
+		}
+	}
+	p.expect(.rbrace, "'}'")!
+	return InterfaceDecl{ name: name.lit, methods: methods, line: t.line }
+}
+
 // parse_fn parses `fn name(params) { }` or a method `fn (p Type) name(params) { }`.
 fn (mut p Parser) parse_fn() !FnDecl {
 	fn_tok := p.expect(.kw_fn, "'fn'")!
@@ -176,18 +213,76 @@ fn (mut p Parser) parse_fn() !FnDecl {
 		p.expect(.rparen, "')'")!
 	}
 	name := p.expect(.ident, 'function name')!
-	params := p.parse_params()!
+	// generic type parameters: fn first[T, U](arr) { ... } — captured so the
+	// type checker can validate call sites; the VM is dynamically typed, so
+	// they erase to a single function at runtime
+	mut type_params := []string{}
+	if p.cur().kind == .lbracket {
+		p.advance()
+		for p.cur().kind != .rbracket {
+			tp := p.expect(.ident, 'type parameter')!.lit
+			if tp in type_params {
+				return error('duplicate type parameter "${tp}" in function ${name.lit} (line ${name.line}, col ${name.col})')
+			}
+			type_params << tp
+			if p.cur().kind == .comma {
+				p.advance()
+			}
+		}
+		p.expect(.rbracket, "']'")!
+	}
+	params, defaults, has_defs, variadic := p.parse_params()!
 	body := p.parse_block()!
-	return FnDecl{ name: name.lit, recv_name: recv_name, recv_type: recv_type, params: params, body: body, line: fn_tok.line }
+	return FnDecl{
+		name: name.lit
+		type_params: type_params
+		recv_name: recv_name
+		recv_type: recv_type
+		params: params
+		defaults: defaults
+		has_defs: has_defs
+		variadic: variadic
+		body: body
+		line: fn_tok.line
+	}
 }
 
-// parse_params parses `(a, b, c)` — the parameter list of a function.
-fn (mut p Parser) parse_params() ![]string {
+// parse_params parses `(a, b, c = expr, rest...)` — the parameter list of a
+// function. Returns the names, the default-value expressions (parallel array,
+// empty Expr{} when no default), whether each has a default, and whether the
+// last parameter is variadic.
+fn (mut p Parser) parse_params() !([]string, []Expr, []bool, bool) {
 	p.expect(.lparen, "'('")!
 	mut params := []string{}
+	mut defaults := []Expr{}
+	mut has_defs := []bool{}
+	mut variadic := false
 	if p.cur().kind != .rparen {
 		for {
-			params << p.expect(.ident, 'parameter name')!.lit
+			name_tok := p.expect(.ident, 'parameter name')!
+			name := name_tok.lit
+			if p.cur().kind == .dotdotdot {
+				// variadic parameter: `rest...` (must be last)
+				p.advance()
+				params << name
+				defaults << Expr{}
+				has_defs << false
+				variadic = true
+				if p.cur().kind == .comma {
+					return error('a variadic parameter must be last (line ${name_tok.line})')
+				}
+				break
+			}
+			mut def := Expr{}
+			mut has_def := false
+			if p.cur().kind == .assign {
+				p.advance()
+				def = p.parse_expr()!
+				has_def = true
+			}
+			params << name
+			defaults << def
+			has_defs << has_def
 			if p.cur().kind == .comma {
 				p.advance()
 				continue
@@ -196,7 +291,7 @@ fn (mut p Parser) parse_params() ![]string {
 		}
 	}
 	p.expect(.rparen, "')'")!
-	return params
+	return params, defaults, has_defs, variadic
 }
 
 fn (mut p Parser) parse_block() ![]Stmt {
@@ -217,6 +312,30 @@ fn (mut p Parser) parse_stmt() !Stmt {
 	match t.kind {
 		.kw_let {
 			p.advance()
+			// destructuring let: `let { a, b } = expr` or `let [a, b] = expr`
+			if p.cur().kind == .lbrace || p.cur().kind == .lbracket {
+				is_field := p.cur().kind == .lbrace
+				p.advance()
+				mut names := []string{}
+				mut closing := TokKind.rbracket
+				if is_field {
+					closing = .rbrace
+				}
+				if p.cur().kind != closing {
+					for {
+						names << p.expect(.ident, 'binding name')!.lit
+						if p.cur().kind == .comma {
+							p.advance()
+							continue
+						}
+						break
+					}
+				}
+				p.expect(closing, "']' or '}'")!
+				p.expect(.assign, "'='")!
+				e := p.parse_expr()!
+				return Stmt{ kind: .destruct_stmt, expr: e, destruct_targets: names, destruct_field: is_field, line: t.line }
+			}
 			name := p.expect(.ident, 'variable name')!
 			p.expect(.assign, "'='")!
 			e := p.parse_expr()!
@@ -257,6 +376,14 @@ fn (mut p Parser) parse_stmt() !Stmt {
 		.kw_for {
 			p.advance()
 			name := p.expect(.ident, 'loop variable')!
+			mut idx_name := ''
+			mut val_name := name.lit
+			if p.cur().kind == .comma {
+				// for i, v in arr { ... }
+				p.advance()
+				idx_name = name.lit
+				val_name = p.expect(.ident, 'loop value variable')!.lit
+			}
 			p.expect(.kw_in, "'in'")!
 			first := p.parse_expr()!
 			if p.cur().kind == .dotdot || p.cur().kind == .dotdotdot {
@@ -264,10 +391,10 @@ fn (mut p Parser) parse_stmt() !Stmt {
 				p.advance()
 				end := p.parse_expr()!
 				body := p.parse_block()!
-				return Stmt{ kind: .for_range_stmt, target: name.lit, expr: first, cond: end, inclusive: inclusive, body: body, line: t.line }
+				return Stmt{ kind: .for_range_stmt, target: val_name, expr: first, cond: end, inclusive: inclusive, body: body, line: t.line }
 			}
 			body := p.parse_block()!
-			return Stmt{ kind: .for_in_stmt, target: name.lit, expr: first, body: body, line: t.line }
+			return Stmt{ kind: .for_in_stmt, target: val_name, idx_target: idx_name, expr: first, body: body, line: t.line }
 		}
 		.kw_return {
 			p.advance()
@@ -297,13 +424,29 @@ fn (mut p Parser) parse_stmt() !Stmt {
 			}
 			return Stmt{ kind: .assert_stmt, expr: e, line: t.line }
 		}
+		.kw_try {
+			p.advance()
+			return p.parse_try_stmt(t)!
+		}
+		.kw_throw {
+			p.advance()
+			e := p.parse_expr()!
+			return Stmt{ kind: .throw_stmt, expr: e, line: t.line }
+		}
 		.ident {
 			p.advance()
+			// generic type args in statement position: first[int](...)
+			mut type_args := []string{}
+			if p.cur().kind == .lbracket && p.looks_like_generic_args() {
+				type_args = p.parse_type_args()!
+			}
 			mut e := Expr{}
 			if p.cur().kind == .lparen {
 				// a call statement: foo(args), optionally chained foo().x
-				e = p.parse_call(t)!
+				e = p.parse_call(t, type_args)!
 				e = p.parse_postfix_tail(e)!
+			} else if type_args.len > 0 {
+				return error('generic type arguments on a non-call "${t.lit}" (line ${t.line}, col ${t.col})')
 			} else {
 				e = p.parse_postfix_tail(Expr{ kind: .ident, name: t.lit, line: t.line })!
 			}
@@ -360,11 +503,11 @@ fn (mut p Parser) parse_stmt() !Stmt {
 		}
 		.kw_print, .kw_println {
 			p.advance()
-			e := p.parse_call(t)!
+			e := p.parse_call(t, [])!
 			return Stmt{ kind: .expr_stmt, expr: e, line: t.line }
 		}
 		else {
-			return error('unexpected token "${t.lit}" at line ${t.line}')
+			return error('unexpected token "${t.lit}" at line ${t.line}, col ${t.col}')
 		}
 	}
 }
@@ -388,6 +531,21 @@ fn (mut p Parser) parse_if(t Tok) !Stmt {
 	return Stmt{ kind: .if_stmt, cond: cond, body: body, els: els, line: t.line }
 }
 
+// parse_try_stmt parses `try { body } catch ident { body }`.
+fn (mut p Parser) parse_try_stmt(t Tok) !Stmt {
+	body := p.parse_block()!
+	p.expect(.kw_catch, "'catch'")!
+	catch_var := p.expect(.ident, 'error variable')!.lit
+	catch_body := p.parse_block()!
+	return Stmt{
+		kind: .try_stmt
+		body: body
+		target: catch_var
+		els: catch_body
+		line: t.line
+	}
+}
+
 // bin_node allocates a binary-operator node. It takes copies of the operands
 // so that `&l`/`&r` target fresh heap objects (taking the address of a local
 // that is later reassigned would create a self-referential node).
@@ -409,6 +567,15 @@ fn index_node(base Expr, idx Expr, line int) Expr {
 	return Expr{ kind: .index, left: &b, right: &i, line: line }
 }
 
+// slice_node builds `base[start..end]`.
+// end uses -1 as sentinel for "open-ended" (slice to end).
+fn slice_node(base Expr, start Expr, end Expr, _inclusive bool, line int) Expr {
+	mut b := base
+	mut s := start
+	mut e := end
+	return Expr{ kind: .slice, left: &b, right: &s, extra: &e, line: line }
+}
+
 // field_node builds `base.name`.
 fn field_node(base Expr, name string, line int) Expr {
 	mut b := base
@@ -436,8 +603,41 @@ fn (mut p Parser) parse_or() !Expr {
 }
 
 fn (mut p Parser) parse_and() !Expr {
-	mut e := p.parse_eq()!
+	mut e := p.parse_bitor()!
 	for p.cur().kind == .kw_and {
+		op := p.advance()
+		rhs := p.parse_bitor()!
+		e = bin_node(op.kind, e, rhs, op.line)
+	}
+	return e
+}
+
+// parse_bitor handles `|` (bitwise OR).
+fn (mut p Parser) parse_bitor() !Expr {
+	mut e := p.parse_bitxor()!
+	for p.cur().kind == .pipe {
+		op := p.advance()
+		rhs := p.parse_bitxor()!
+		e = bin_node(op.kind, e, rhs, op.line)
+	}
+	return e
+}
+
+// parse_bitxor handles `^` (bitwise XOR).
+fn (mut p Parser) parse_bitxor() !Expr {
+	mut e := p.parse_bitand()!
+	for p.cur().kind == .caret {
+		op := p.advance()
+		rhs := p.parse_bitand()!
+		e = bin_node(op.kind, e, rhs, op.line)
+	}
+	return e
+}
+
+// parse_bitand handles `&` (bitwise AND).
+fn (mut p Parser) parse_bitand() !Expr {
+	mut e := p.parse_eq()!
+	for p.cur().kind == .amp {
 		op := p.advance()
 		rhs := p.parse_eq()!
 		e = bin_node(op.kind, e, rhs, op.line)
@@ -456,8 +656,19 @@ fn (mut p Parser) parse_eq() !Expr {
 }
 
 fn (mut p Parser) parse_rel() !Expr {
-	mut e := p.parse_add()!
+	mut e := p.parse_shift()!
 	for p.cur().kind == .lt || p.cur().kind == .le || p.cur().kind == .gt || p.cur().kind == .ge {
+		op := p.advance()
+		rhs := p.parse_shift()!
+		e = bin_node(op.kind, e, rhs, op.line)
+	}
+	return e
+}
+
+// parse_shift handles `<<` and `>>` (bitwise shift).
+fn (mut p Parser) parse_shift() !Expr {
+	mut e := p.parse_add()!
+	for p.cur().kind == .lt_lt || p.cur().kind == .gt_gt {
 		op := p.advance()
 		rhs := p.parse_add()!
 		e = bin_node(op.kind, e, rhs, op.line)
@@ -487,7 +698,7 @@ fn (mut p Parser) parse_mul() !Expr {
 
 fn (mut p Parser) parse_unary() !Expr {
 	t := p.cur()
-	if t.kind == .kw_not || t.kind == .minus {
+	if t.kind == .kw_not || t.kind == .minus || t.kind == .tilde {
 		p.advance()
 		e := p.parse_unary()!
 		return unary_node(t.kind, e, t.line)
@@ -514,8 +725,22 @@ fn (mut p Parser) parse_postfix_tail(e Expr) !Expr {
 		if p.cur().kind == .lbracket {
 			p.advance()
 			idx := p.parse_expr()!
-			p.expect(.rbracket, "']'")!
-			cur = index_node(cur, idx, cur.line)
+			if p.cur().kind == .dotdot || p.cur().kind == .dotdotdot {
+				// arr[start..end] or arr[start..] slicing
+				p.advance()
+				if p.cur().kind == .rbracket {
+					// arr[start..] — slice to end
+					p.advance()
+					cur = slice_node(cur, idx, Expr{ kind: .int_lit, int_v: -1, line: cur.line }, false, cur.line)
+				} else {
+					end := p.parse_expr()!
+					p.expect(.rbracket, "']'")!
+					cur = slice_node(cur, idx, end, false, cur.line)
+				}
+			} else {
+				p.expect(.rbracket, "']'")!
+				cur = index_node(cur, idx, cur.line)
+			}
 			continue
 		}
 		if p.cur().kind == .dot {
@@ -542,10 +767,18 @@ fn (mut p Parser) parse_primary() !Expr {
 			p.advance()
 			return Expr{ kind: .int_lit, int_v: t.lit.i64(), line: t.line }
 		}
+		.float_lit {
+			p.advance()
+			return Expr{ kind: .float_lit, float_v: t.lit.f64(), line: t.line }
+		}
 		.str_lit {
 			p.advance()
 			return Expr{ kind: .str_lit, str_v: t.lit, line: t.line }
 		}
+		.str_interp {
+			p.advance()
+			return p.parse_str_interp(t)!
+		}
 		.kw_true {
 			p.advance()
 			return Expr{ kind: .bool_lit, int_v: 1, line: t.line }
@@ -594,24 +827,52 @@ fn (mut p Parser) parse_primary() !Expr {
 		}
 		.kw_print, .kw_println {
 			p.advance()
-			return p.parse_call(t)!
+			return p.parse_call(t, [])!
+		}
+		.kw_fn {
+			// anonymous function expression: fn(params) { body }
+			p.advance()
+			return p.parse_anon_fn(t)!
 		}
 		else {
-			return error('unexpected token "${t.lit}" at line ${t.line}')
+			return error('unexpected token "${t.lit}" at line ${t.line}, col ${t.col}')
 		}
 	}
 }
 
 fn (mut p Parser) parse_call_or_ident(t Tok) !Expr {
+	// generic type args: first[int](...) — captured for the type checker;
+	// only treated as type args when [ is followed by idents then ] then (
+	mut type_args := []string{}
+	if p.cur().kind == .lbracket && p.looks_like_generic_args() {
+		type_args = p.parse_type_args()!
+	}
 	if p.cur().kind == .lparen {
-		return p.parse_call(t)!
+		return p.parse_call(t, type_args)!
+	}
+	if type_args.len > 0 {
+		return error('generic type arguments on a non-call "${t.lit}" (line ${t.line}, col ${t.col})')
 	}
 	return Expr{ kind: .ident, name: t.lit, line: t.line }
 }
 
-fn (mut p Parser) parse_call(name Tok) !Expr {
+// parse_type_args parses `[int, string]` into a list of type names.
+fn (mut p Parser) parse_type_args() ![]string {
+	p.advance() // consume '['
+	mut args := []string{}
+	for p.cur().kind != .rbracket {
+		args << p.expect(.ident, 'type argument')!.lit
+		if p.cur().kind == .comma {
+			p.advance()
+		}
+	}
+	p.expect(.rbracket, "']'")!
+	return args
+}
+
+fn (mut p Parser) parse_call(name Tok, type_args []string) !Expr {
 	args := p.parse_args()!
-	return Expr{ kind: .call, name: name.lit, args: args, line: name.line }
+	return Expr{ kind: .call, name: name.lit, type_args: type_args, args: args, line: name.line }
 }
 
 // parse_args parses `(e1, e2, ...)` and returns the argument expressions.
@@ -668,3 +929,113 @@ fn (mut p Parser) looks_like_struct_lit() bool {
 	// typed struct literal: `{ ident :` or map literal: `{ "key" :`
 	return (p.toks[p.pos + 1].kind == .ident || p.toks[p.pos + 1].kind == .str_lit) && p.toks[p.pos + 2].kind == .colon
 }
+
+// looks_like_generic_args checks if `[` starts generic type args like `[T]` or `[T, U]`
+// rather than array indexing. It peeks ahead to see `ident ... ] (`.
+fn (mut p Parser) looks_like_generic_args() bool {
+	// current token must be lbracket (the caller already checked this)
+	if p.pos + 2 >= p.toks.len {
+		return false
+	}
+	// must start with an ident after the [
+	if p.toks[p.pos + 1].kind != .ident {
+		return false
+	}
+	// scan forward: ident, comma, ident, ..., rbracket, then lparen
+	mut i := p.pos + 2
+	for i < p.toks.len && p.toks[i].kind != .rbracket {
+		if p.toks[i].kind != .ident && p.toks[i].kind != .comma {
+			return false
+		}
+		i++
+	}
+	if i >= p.toks.len {
+		return false
+	}
+	// p.toks[i] should be rbracket
+	if i + 1 >= p.toks.len {
+		return false
+	}
+	return p.toks[i + 1].kind == .lparen
+}
+
+// parse_str_interp handles string interpolation: "hello ${name} ${age}".
+// It splits the raw string into alternating text/expression parts and builds
+// a chain of + concatenations so the compiler needs no special handling.
+fn (mut p Parser) parse_str_interp(t Tok) !Expr {
+	parts := split_str_interp(t.lit)
+	// parts alternates: text, expr, text, expr, ..., text
+	if parts.len == 1 {
+		return Expr{ kind: .str_lit, str_v: parts[0], line: t.line }
+	}
+	// build the first string part
+	mut result := Expr{ kind: .str_lit, str_v: parts[0], line: t.line }
+	mut i := 1
+	for i < parts.len {
+		// parts[i] is an expression — tokenise and parse it
+		expr_src := parts[i]
+		expr_toks := tokenize(expr_src)!
+		mut ep := Parser{ toks: expr_toks }
+		expr := ep.parse_expr()!
+		result = bin_node(.plus, result, expr, t.line)
+		i++
+		// parts[i] is the next text fragment
+		if i < parts.len {
+			if parts[i].len > 0 {
+				str_e := Expr{ kind: .str_lit, str_v: parts[i], line: t.line }
+				result = bin_node(.plus, result, str_e, t.line)
+			}
+			i++
+		}
+	}
+	return result
+}
+
+// parse_anon_fn parses an anonymous function expression: `fn(params) { body }`.
+fn (mut p Parser) parse_anon_fn(t Tok) !Expr {
+	params, defaults, has_defs, variadic := p.parse_params()!
+	body := p.parse_block()!
+	return Expr{
+		kind: .anon_fn
+		fparams: params
+		fdefaults: defaults
+		fhas_defs: has_defs
+		fvariadic: variadic
+		fn_body: body
+		line: t.line
+	}
+}
+
+// split_str_interp splits an interpolated string at ${...} boundaries.
+// Returns alternating [text, expr, text, expr, ..., text] fragments.
+fn split_str_interp(s string) []string {
+	mut parts := []string{}
+	mut i := 0
+	mut current := ''
+	for i < s.len {
+		if s[i] == `$` && i + 1 < s.len && s[i + 1] == `{` {
+		parts << current
+		current = ''
+		i += 2
+		mut depth := 1
+		mut expr := ''
+		for i < s.len && depth > 0 {
+			if s[i] == `{` {
+				depth++
+			} else if s[i] == `}` {
+				depth--
+			}
+			if depth > 0 {
+				expr += s[i].ascii_str()
+			}
+			i++
+		}
+		parts << expr
+	} else {
+		current += s[i].ascii_str()
+		i++
+	}
+}
+	parts << current
+	return parts
+}
diff --git a/compiler/tokens.v b/compiler/tokens.v
index 8230085..3a1f201 100644
--- a/compiler/tokens.v
+++ b/compiler/tokens.v
@@ -5,7 +5,9 @@ pub enum TokKind {
 	eof
 	ident
 	int_lit
+	float_lit
 	str_lit
+	str_interp
 	lparen
 	rparen
 	lbrace
@@ -20,6 +22,12 @@ pub enum TokKind {
 	star
 	slash
 	percent
+	amp
+	pipe
+	caret
+	tilde
+	lt_lt
+	gt_gt
 	eq_eq
 	not_eq
 	lt
@@ -56,6 +64,10 @@ pub enum TokKind {
 	kw_import
 	kw_enum
 	kw_const
+	kw_interface
+	kw_try
+	kw_catch
+	kw_throw
 }
 
 pub struct Tok {
@@ -63,4 +75,5 @@ pub:
 	kind TokKind
 	lit  string
 	line int
+	col  int // 1-based column within the line
 }
diff --git a/examples/for_index.vr b/examples/for_index.vr
new file mode 100644
index 0000000..e034e4a
--- /dev/null
+++ b/examples/for_index.vr
@@ -0,0 +1,35 @@
+// for i, v in arr — iterate with both index and value
+
+fn main() {
+    let fruits = ["apple", "banana", "cherry"]
+    
+    // basic indexed iteration
+    for i, v in fruits {
+        println("${i}: ${v}")
+    }
+    
+    // use the index for computation
+    let nums = [10, 20, 30, 40, 50]
+    let sum = 0
+    for i, v in nums {
+        if i % 2 == 0 {
+            sum += v
+        }
+    }
+    println("sum of even-indexed elements: ${sum}")
+    
+    // build a new array using index
+    let letters = ["a", "b", "c", "d"]
+    let tagged = []
+    for i, v in letters {
+        push(tagged, "${v}${i}")
+    }
+    println(tagged)
+    
+    // plain for-in still works (no index)
+    for v in fruits {
+        print(v)
+        print(" ")
+    }
+    println("")
+}
diff --git a/examples/generics.vr b/examples/generics.vr
new file mode 100644
index 0000000..f3a2691
--- /dev/null
+++ b/examples/generics.vr
@@ -0,0 +1,26 @@
+// generic function syntax (V-style type parameters)
+
+// generic functions: type params are parsed but the VM handles types dynamically
+fn first[T](arr) {
+    return arr[0]
+}
+
+fn last[T](arr) {
+    let n = len(arr)
+    return arr[n - 1]
+}
+
+fn main() {
+    // works with integers
+    let nums = [10, 20, 30]
+    println("first num: ${first[int](nums)}")
+    println("last num: ${last[int](nums)}")
+    
+    // works with strings
+    let words = ["hello", "world", "foo"]
+    println("first word: ${first[string](words)}")
+    println("last word: ${last[string](words)}")
+    
+    // type args are optional (VM is dynamically typed)
+    println("first (no type arg): ${first(nums)}")
+}
diff --git a/examples/interpolation.vr b/examples/interpolation.vr
new file mode 100644
index 0000000..82d0b98
--- /dev/null
+++ b/examples/interpolation.vr
@@ -0,0 +1,33 @@
+// string interpolation: embed expressions inside "..." with ${}
+
+fn main() {
+    let name = "alice"
+    let age = 30
+    
+    // simple variable interpolation
+    println("hello ${name}!")
+    
+    // multiple interpolations
+    println("${name} is ${age} years old")
+    
+    // expression inside interpolation
+    println("${name} will be ${age + 1} next year")
+    
+    // interpolation with function calls
+    let nums = [10, 20, 30]
+    println("first element: ${nums[0]}")
+    
+    // string concatenation with interpolation
+    let greeting = "hi"
+    println("${greeting}, ${name}! age=${age}")
+    
+    // no interpolation (regular string)
+    println("no interpolation here")
+    
+    // empty interpolation adjacent to text
+    let x = 42
+    println("value is ${x}")
+    
+    // arithmetic in interpolation
+    println("double age: ${age * 2}")
+}
diff --git a/examples/slicing.vr b/examples/slicing.vr
new file mode 100644
index 0000000..b6b80cc
--- /dev/null
+++ b/examples/slicing.vr
@@ -0,0 +1,44 @@
+// array and string slicing: arr[1..3], arr[1:], str[0..5]
+
+fn main() {
+    // --- array slicing ---
+    let nums = [10, 20, 30, 40, 50]
+    
+    // basic slice: arr[start..end]
+    let mid = nums[1..3]
+    println(mid)          // [20, 30]
+    
+    // slice from start
+    let first_two = nums[0..2]
+    println(first_two)    // [10, 20]
+    
+    // slice to end (open-ended)
+    let tail = nums[2..]
+    println(tail)         // [30, 40, 50]
+    
+    // single element slice
+    let single = nums[3..4]
+    println(single)       // [40]
+    
+    // --- string slicing ---
+    let greeting = "hello, world!"
+    
+    // basic substring
+    let hello = greeting[0..5]
+    println(hello)        // "hello"
+    
+    // slice from index
+    let world = greeting[7..]
+    println(world)        // "world!"
+    
+    // slice to index
+    let hello_comma = greeting[0..6]
+    println(hello_comma)  // "hello,"
+    
+    // --- slicing in expressions ---
+    let data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+    let first = data[0..3]
+    let last = data[7..]
+    println(first)
+    println(last)
+}
diff --git a/fmt.v b/fmt.v
new file mode 100644
index 0000000..59df6ee
--- /dev/null
+++ b/fmt.v
@@ -0,0 +1,104 @@
+// fmt.v — `vr fmt`: a source formatter for VuurRaaf.
+//
+// Works line-by-line: it fixes indentation from brace depth, trims stray
+// whitespace, collapses space runs outside string literals, and preserves
+// every comment (whole-line and inline). It never reorders or rewrites code.
+//
+//   vr fmt file.vr        print the formatted source to stdout
+//   vr fmt -w file.vr     rewrite the file in place
+module main
+
+import os
+
+fn toolchain_fmt(args []string) ! {
+	if args.len == 0 {
+		return error('usage: vr fmt [-w] <file.vr>')
+	}
+	mut write := false
+	mut files := []string{}
+	for a in args {
+		if a == '-w' || a == '--write' {
+			write = true
+		} else {
+			files << a
+		}
+	}
+	if files.len == 0 {
+		return error('usage: vr fmt [-w] <file.vr>')
+	}
+	for f in files {
+		src := os.read_file(f) or { return error('cannot read "${f}": ${err.msg()}') }
+		formatted := fmt_source(src)
+		if write {
+			os.write_file(f, formatted) or { return error('cannot write "${f}": ${err.msg()}') }
+			println('formatted ${f}')
+		} else {
+			print(formatted)
+		}
+	}
+}
+
+// fmt_source normalizes a whole source file. Comment lines are indented with
+// the surrounding depth; closing braces drop one level like the code does.
+fn fmt_source(src string) string {
+	mut out := ''
+	mut depth := 0
+	for raw in src.split_into_lines() {
+		line := raw.trim_space()
+		if line == '' {
+			out += '\n'
+			continue
+		}
+		d := brace_delta(line)
+		mut indent := depth
+		if line.starts_with('}') && depth > 0 {
+			indent = depth - 1
+		}
+		out += '\t'.repeat(indent) + collapse_spaces(line) + '\n'
+		depth += d
+		if depth < 0 {
+			depth = 0
+		}
+	}
+	return out
+}
+
+// collapse_spaces replaces runs of spaces outside of string literals with a
+// single space, so indentation and padding become canonical without touching
+// string contents.
+fn collapse_spaces(line string) string {
+	mut out := ''
+	mut in_str := false
+	mut i := 0
+	for i < line.len {
+		c := line[i]
+		if c == `"` {
+			in_str = !in_str
+			out += c.ascii_str()
+			i++
+			continue
+		}
+		if in_str && c == `\\` {
+			out += c.ascii_str()
+			i++
+			if i < line.len {
+				out += line[i].ascii_str()
+				i++
+			}
+			continue
+		}
+		if !in_str && c == ` ` {
+			for i < line.len && line[i] == ` ` {
+				i++
+			}
+			out += ' '
+			continue
+		}
+		out += c.ascii_str()
+		i++
+	}
+	return out
+}
+
+// brace_delta is shared with the REPL (repl.v): it tokenizes the line so
+// braces inside string literals do not affect depth.
diff --git a/linker/linker.v b/linker/linker.v
index d543add..07eccf9 100644
--- a/linker/linker.v
+++ b/linker/linker.v
@@ -15,6 +15,7 @@ pub fn link(paths []string, out string) ! {
 	mut strings := []string{}
 	mut symbols := map[string]int{}
 	mut relocs := []obj.Reloc{}
+	mut lines := []obj.LineInfo{}
 	for p in paths {
 		o := obj.read(p)!
 		base := code.len
@@ -28,6 +29,9 @@ pub fn link(paths []string, out string) ! {
 		for r in o.relocs {
 			relocs << obj.Reloc{ offset: r.offset + u32(base), name: r.name, kind: r.kind }
 		}
+		for l in o.lines {
+			lines << obj.LineInfo{ off: l.off + u32(base), line: l.line }
+		}
 	}
 	// resolve relocations
 	for r in relocs {
@@ -47,7 +51,7 @@ pub fn link(paths []string, out string) ! {
 	for name, entry in symbols {
 		fns << obj.BinFn{ name: name, entry: entry }
 	}
-	obj.write_bin(out, obj.Bin{ fns: fns, strings: strings, code: code })!
+	obj.write_bin(out, obj.Bin{ fns: fns, strings: strings, code: code, lines: lines })!
 }
 
 fn intern_str(mut table []string, s string) int {
diff --git a/main.v b/main.v
index 61b209d..78fe250 100644
--- a/main.v
+++ b/main.v
@@ -70,6 +70,24 @@ fn main() {
 		'bench', 'b' {
 			toolchain_bench(rest) or { die('bench', err) }
 		}
+		'repl', 'i' {
+			toolchain_repl() or { die('repl', err) }
+		}
+		'fmt' {
+			toolchain_fmt(rest) or { die('fmt', err) }
+		}
+		'init' {
+			toolchain_init(rest) or { die('init', err) }
+		}
+		'get' {
+			toolchain_get(rest) or { die('get', err) }
+		}
+		'install' {
+			toolchain_install() or { die('install', err) }
+		}
+		'list' {
+			toolchain_list() or { die('list', err) }
+		}
 		'clean' {
 			toolchain_clean()
 		}
@@ -153,6 +171,12 @@ fn toolchain_help() {
 	println('  debug <file.vr|file.vbin>                run with an instruction trace')
 	println('  test <file.vr>                           run every test_* function')
 	println('  bench <file.vr> [iterations]             benchmark main()')
+	println('  repl                                     interactive session')
+	println('  fmt [-w] <file.vr>                       format source')
+	println('  init [name]                              scaffold a project')
+	println('  get <owner/repo | url | ./path>          fetch a package into vendor/')
+	println('  install                                  install deps from vr.mod')
+	println('  list                                     show the project manifest')
 	println('  clean                                    remove build artifacts')
 	println('  up                                       rebuild the vr binary into bin/')
 	println('  symlink                                  link bin/vr into your PATH')
@@ -311,16 +335,17 @@ fn toolchain_link(args []string) ! {
 
 fn toolchain_run(args []string) ! {
 	if args.len == 0 {
-		return error('usage: vr run <file.vr|file.vbin>')
+		return error('usage: vr run <file.vr|file.vbin> [program-args...]')
 	}
 	f := args[0]
+	prog_args := args[1..]
 	if f.ends_with('.vbin') {
 		bin := obj.read_bin(f)!
-		vm.run(bin, 'main', false)!
+		vm.run_with_args(bin, 'main', false, prog_args)!
 		return
 	}
 	if f.ends_with('.vr') {
-		run_src(f, 'main', false)!
+		run_src_with_args(f, 'main', false, prog_args)!
 		return
 	}
 	return error('unsupported file type: ${f} (expected .vr or .vbin)')
@@ -423,6 +448,10 @@ fn toolchain_bench(args []string) ! {
 }
 
 fn run_src(src string, entry string, trace bool) ! {
+	run_src_with_args(src, entry, trace, []string{})!
+}
+
+fn run_src_with_args(src string, entry string, trace bool, args []string) ! {
 	tmp_obj := os.join_path(os.temp_dir(), 'vr_${os.getpid()}.vobj')
 	tmp_bin := os.join_path(os.temp_dir(), 'vr_${os.getpid()}.vbin')
 	defer {
@@ -433,7 +462,7 @@ fn run_src(src string, entry string, trace bool) ! {
 	obj.write(tmp_obj, o)!
 	linker.link([tmp_obj], tmp_bin)!
 	bin := obj.read_bin(tmp_bin)!
-	vm.run(bin, entry, trace)!
+	vm.run_with_args(bin, entry, trace, args)!
 }
 
 // ---------------------------------------------------------------------------
diff --git a/obj/obj.v b/obj/obj.v
index f8a4e1c..0fa6a53 100644
--- a/obj/obj.v
+++ b/obj/obj.v
@@ -13,6 +13,7 @@
 module obj
 
 import os
+import math
 
 pub const magic = 'VROBJ'
 pub const bin_magic = 'VRBIN'
@@ -36,6 +37,7 @@ pub mut:
 	strings []string
 	code    []u8
 	relocs  []Reloc
+	lines   []LineInfo
 }
 
 pub struct BinFn {
@@ -44,11 +46,20 @@ pub mut:
 	entry int
 }
 
+// LineInfo maps a code offset to the source line it was generated from,
+// enabling source-level locations in runtime errors.
+pub struct LineInfo {
+pub mut:
+	off  u32
+	line int
+}
+
 pub struct Bin {
 pub mut:
 	fns     []BinFn
 	strings []string
 	code    []u8
+	lines   []LineInfo
 }
 
 // ---------------------------------------------------------------------------
@@ -66,6 +77,16 @@ pub fn encode_i64(v i64) []u8 {
 	return b
 }
 
+// encode_f64 writes a little-endian f64 (its IEEE-754 bit pattern).
+pub fn encode_f64(v f64) []u8 {
+	bits := math.f64_bits(v)
+	mut b := []u8{}
+	for i in 0..8 {
+		b << u8((bits >> (8 * i)) & 0xff)
+	}
+	return b
+}
+
 // patch_i64 writes a little-endian i64 over `code[off..off+8]`.
 pub fn patch_i64(mut code []u8, off u32, v i64) {
 	for i in 0..8 {
@@ -146,6 +167,11 @@ pub fn write(path string, o Obj) ! {
 		b << r.name.bytes()
 		b << r.kind
 	}
+	b << encode_u32(u32(o.lines.len))
+	for l in o.lines {
+		b << encode_u32(l.off)
+		b << encode_i64(i64(l.line))
+	}
 	os.write_bytes(path, b)!
 }
 
@@ -180,6 +206,12 @@ pub fn read(path string) !Obj {
 		kind := r.u8_()!
 		o.relocs << Reloc{ offset: off, name: name, kind: kind }
 	}
+	nlines := int(r.u32_()!)
+	for _ in 0..nlines {
+		off := r.u32_()!
+		line := int(r.i64_()!)
+		o.lines << LineInfo{ off: off, line: line }
+	}
 	return o
 }
 
@@ -203,6 +235,11 @@ pub fn write_bin(path string, bin Bin) ! {
 	}
 	b << encode_u32(u32(bin.code.len))
 	b << bin.code
+	b << encode_u32(u32(bin.lines.len))
+	for l in bin.lines {
+		b << encode_u32(l.off)
+		b << encode_i64(i64(l.line))
+	}
 	os.write_bytes(path, b)!
 }
 
@@ -229,5 +266,12 @@ pub fn read_bin(path string) !Bin {
 		return error('executable file truncated')
 	}
 	bin.code = b[r.pos..r.pos + ncode]
+	r.pos += ncode
+	nlines := int(r.u32_()!)
+	for _ in 0..nlines {
+		off := r.u32_()!
+		line := int(r.i64_()!)
+		bin.lines << LineInfo{ off: off, line: line }
+	}
 	return bin
 }
diff --git a/pkg.v b/pkg.v
new file mode 100644
index 0000000..6e29901
--- /dev/null
+++ b/pkg.v
@@ -0,0 +1,151 @@
+// pkg.v — `vr init` / `vr get` / `vr install`: a minimal package manager.
+//
+// Packages are fetched into ./vendor/<name>/ and recorded in vr.mod as
+// `dep "<spec>"`. The compiler resolves `import "pkg/file"` against vendor/
+// automatically (see compiler/compiler.v). Supported package specs:
+//
+//   vr get owner/repo         clone from GitHub (https://github.com/owner/repo)
+//   vr get https://host/repo  clone any git repository
+//   vr get ./local/path       copy a local directory
+module main
+
+import os
+
+const manifest_file = 'vr.mod'
+const vendor_dir = 'vendor'
+
+fn toolchain_init(args []string) ! {
+	pkg := if args.len > 0 { args[0] } else { os.base(os.getwd()) }
+	if os.exists(manifest_file) {
+		return error('${manifest_file} already exists here')
+	}
+	os.write_file(manifest_file, 'module ${pkg}\nversion 0.1.0\n\n# deps:\n# dep "owner/repo"\n')!
+	os.mkdir('vendor') or {}
+	if !os.exists('main.vr') {
+		os.write_file('main.vr', 'fn main() {\n\tprintln("hello from ${pkg}")\n}\n')!
+	}
+	println('initialized project "${pkg}" (${manifest_file}, main.vr)')
+}
+
+fn toolchain_get(args []string) ! {
+	if args.len == 0 {
+		return error('usage: vr get <owner/repo | git-url | ./path>')
+	}
+	spec := args[0]
+	// determine the package name and how to fetch it
+	mut pkg := ''
+	if spec.starts_with('./') || spec.starts_with('/') {
+		pkg = os.base(spec)
+	} else if spec.contains('://') {
+		pkg = os.base(spec)
+	} else if spec.contains('/') {
+		pkg = spec.all_after('/')
+	} else {
+		pkg = spec
+	}
+	if pkg.ends_with('.git') {
+		pkg = pkg[..pkg.len - 4]
+	}
+	if pkg == '' || pkg == '.' {
+		return error('cannot derive a package name from "${spec}"')
+	}
+	os.mkdir(vendor_dir) or {}
+	dst := os.join_path(vendor_dir, pkg)
+	if os.exists(dst) {
+		return error('package "${pkg}" already exists at ${dst}')
+	}
+	if spec.starts_with('./') || spec.starts_with('/') {
+		copy_dir(spec, dst) or { return error('cannot copy ${spec}: ${err.msg()}') }
+	} else {
+		url := if spec.contains('://') { spec } else { 'https://github.com/${spec}.git' }
+		println('cloning ${url} -> ${dst} ...')
+		r := os.exec(['git', 'clone', '--depth', '1', url, dst])
+		if r.exit_code != 0 {
+			return error('git clone failed: ${r.output}')
+		}
+	}
+	// record the dependency in the manifest (idempotent)
+	if os.exists(manifest_file) {
+		manifest := os.read_file(manifest_file) or { '' }
+		if !manifest.contains('dep "${spec}"') {
+			os.write_file(manifest_file, manifest.trim_space() + '\ndep "${spec}"\n') or {
+				return error('cannot update ${manifest_file}: ${err.msg()}')
+			}
+		}
+	}
+	println('added package "${pkg}" (${spec})')
+}
+
+fn toolchain_install() ! {
+	if !os.exists(manifest_file) {
+		return error('no ${manifest_file} found — run `vr init` first')
+	}
+	manifest := os.read_file(manifest_file)!
+	mut n := 0
+	for line in manifest.split_into_lines() {
+		t := line.trim_space()
+		if !t.starts_with('dep "') {
+			continue
+		}
+		mut spec := t[5..]
+		if spec.ends_with('"') {
+			spec = spec[..spec.len - 1]
+		}
+		if spec == '' {
+			continue
+		}
+		n++
+		toolchain_get([spec]) or { eprintln('  install: ${err.msg()}') }
+	}
+	if n == 0 {
+		println('no dependencies in ${manifest_file}')
+		return
+	}
+	println('installed ${n} package(s) into ${vendor_dir}/')
+}
+
+// copy_dir recursively copies a local directory tree.
+fn copy_dir(src string, dst string) ! {
+	if !os.is_dir(src) {
+		return error('${src} is not a directory')
+	}
+	os.mkdir_all(dst) or { return error('cannot create ${dst}: ${err.msg()}') }
+	for entry in os.ls(src) or { return error('cannot read ${src}: ${err.msg()}') } {
+		sp := os.join_path(src, entry)
+		dp := os.join_path(dst, entry)
+		if os.is_dir(sp) {
+			copy_dir(sp, dp)!
+		} else if os.is_file(sp) {
+			os.cp(sp, dp, os.CopyParams{}) or { return error('cannot copy ${sp}: ${err.msg()}') }
+		}
+	}
+}
+
+fn toolchain_list() ! {
+	if !os.exists(manifest_file) {
+		return error('no ${manifest_file} found here')
+	}
+	manifest := os.read_file(manifest_file)!
+	mod_name := manifest.all_before('\n').replace('module ', '').trim_space()
+	println('project: ${mod_name}')
+	mut found := false
+	for line in manifest.split_into_lines() {
+		t := line.trim_space()
+		if t.starts_with('dep "') {
+			found = true
+			mut spec := t[5..]
+			if spec.ends_with('"') {
+				spec = spec[..spec.len - 1]
+			}
+			mut pkg := os.base(spec)
+			if pkg.ends_with('.git') {
+				pkg = pkg[..pkg.len - 4]
+			}
+			status := if os.exists(os.join_path(vendor_dir, pkg)) { 'installed' } else { 'missing' }
+			println('  ${pkg}  (${status})  <- ${spec}')
+		}
+	}
+	if !found {
+		println('  (no dependencies)')
+	}
+}
diff --git a/repl.v b/repl.v
new file mode 100644
index 0000000..a58bcbd
--- /dev/null
+++ b/repl.v
@@ -0,0 +1,203 @@
+// repl.v — an interactive read-eval-print loop for VuurRaaf.
+//
+// The REPL keeps two growing buffers: top-level declarations (fn / struct /
+// enum / const / import / interface) and persistent statements (let, assert,
+// assignment). Every other line — expressions, println, if/while/for blocks,
+// match, try — is transient: it is evaluated once against the accumulated
+// state and its output is not repeated on later lines. Expressions are
+// echoed like Python's REPL (1 + 1 prints 2); statement keywords run for
+// their side effects.
+//
+//   > let x = 5
+//   > x * 2
+//   10
+//   > fn square(n) { return n * n }
+//   > square(9)
+//   81
+//
+// Multi-line input is gathered while braces are unbalanced:
+//
+//   > fn fib(n) {
+//   ...   if n < 2 { return n }
+//   ...   return fib(n - 1) + fib(n - 2)
+//   ... }
+module main
+
+import os
+import obj
+import compiler
+import linker
+import vm
+
+fn toolchain_repl() ! {
+	println('VuurRaaf ${version} — type :help for commands, :quit to exit')
+	mut top := ''    // fn / struct / enum / const / import declarations
+	mut body := ''   // persistent statements (let / assert / assignment)
+	mut pending := '' // accumulated multi-line input
+	mut depth := 0   // brace balance of pending input
+	for {
+		prompt := if depth > 0 { '... ' } else { '> ' }
+		line := os.input(prompt)
+		if line == '' {
+			continue
+		}
+		trimmed := line.trim_space()
+		if trimmed.starts_with(':') && depth == 0 {
+			act := repl_meta(trimmed)
+			if act == 1 {
+				break
+			}
+			if act == 2 {
+				top = ''
+				body = ''
+				println('session reset')
+			}
+			continue
+		}
+		// gather multi-line input until braces balance
+		pending += line + '\n'
+		depth += brace_delta(line)
+		if depth > 0 {
+			continue
+		}
+		block := pending
+		pending = ''
+		depth = 0
+		match repl_classify(block) {
+			'top' {
+				// fn / struct / enum / const / import — compile-time only
+				candidate := top + '\n' + block
+				if repl_compile(candidate, body, '') {
+					top = candidate
+				}
+			}
+			'body' {
+				candidate := body + '\n' + block
+				if repl_compile(top, candidate, '') {
+					body = candidate
+				}
+			}
+			else {
+				// transient: run once against the accumulated state
+				tail := if repl_is_expr(block) { 'println(${block.trim_space()})' } else { block }
+				repl_compile(top, body, tail)
+			}
+		}
+	}
+}
+
+// repl_meta handles :quit / :reset / :help. Returns 1 to quit, 2 to reset,
+// and 0 otherwise.
+fn repl_meta(cmd string) int {
+	match cmd {
+		':q', ':quit', ':exit' {
+			println('bye')
+			return 1
+		}
+		':reset' {
+			return 2
+		}
+		':help', ':h' {
+			println('  :help          this help')
+			println('  :quit  :exit   leave the REPL')
+			println('  :reset         clear all definitions')
+			println('  expressions are echoed; let/assign/fn persist')
+		}
+		else {
+			eprintln('repl: unknown command "${cmd}" (:help for a list)')
+		}
+	}
+	return 0
+}
+
+// repl_compile compiles top declarations plus a main body (with an optional
+// trailing tail statement), links, runs, and reports errors without exiting.
+// Returns true when the program compiled and ran cleanly.
+fn repl_compile(top string, body string, tail string) bool {
+	src := top + '\nfn main() {\n' + body + '\n' + tail + '\n}'
+	o := compiler.compile(src) or {
+		eprintln('repl: ${err.msg()}')
+		return false
+	}
+	tmp_obj := os.join_path(os.temp_dir(), 'vr_repl_${os.getpid()}.vobj')
+	tmp_bin := os.join_path(os.temp_dir(), 'vr_repl_${os.getpid()}.vbin')
+	defer {
+		os.rm(tmp_obj) or {}
+		os.rm(tmp_bin) or {}
+	}
+	obj.write(tmp_obj, o) or {
+		eprintln('repl: ${err.msg()}')
+		return false
+	}
+	linker.link([tmp_obj], tmp_bin) or {
+		eprintln('repl: ${err.msg()}')
+		return false
+	}
+	bin := obj.read_bin(tmp_bin) or {
+		eprintln('repl: ${err.msg()}')
+		return false
+	}
+	vm.run(bin, 'main', false) or {
+		eprintln('repl: ${err.msg()}')
+		return false
+	}
+	return true
+}
+
+// repl_classify buckets a (possibly multi-line) input block.
+fn repl_classify(block string) string {
+	toks := compiler.tokenize(block) or { return 'transient' }
+	if toks.len == 0 {
+		return 'transient'
+	}
+	match toks[0].kind {
+		.kw_fn, .kw_struct, .kw_enum, .kw_const, .kw_import, .kw_interface {
+			return 'top'
+		}
+		.kw_let, .kw_assert {
+			return 'body'
+		}
+		.ident {
+			// assignment persists; anything else is an expression
+			if toks.len >= 2 && toks[1].kind in [.assign, .plus_eq, .minus_eq, .star_eq, .slash_eq] {
+				return 'body'
+			}
+			return 'transient'
+		}
+		else {
+			return 'transient'
+		}
+	}
+}
+
+// repl_is_expr reports whether a transient block is a bare expression that
+// should be echoed (as opposed to a statement keyword like println or if).
+fn repl_is_expr(block string) bool {
+	toks := compiler.tokenize(block) or { return false }
+	if toks.len == 0 {
+		return false
+	}
+	match toks[0].kind {
+		.kw_print, .kw_println, .kw_if, .kw_while, .kw_for, .kw_match, .kw_break, .kw_continue, .kw_return, .kw_try, .kw_throw {
+			return false
+		}
+		else {
+			return true
+		}
+	}
+}
+
+// brace_delta counts the brace balance of a line using the tokenizer, so
+// braces inside string literals do not confuse continuation detection.
+fn brace_delta(line string) int {
+	toks := compiler.tokenize(line) or { return 0 }
+	mut d := 0
+	for t in toks {
+		if t.kind == .lbrace {
+			d++
+		} else if t.kind == .rbrace {
+			d--
+		}
+	}
+	return d
+}
diff --git a/vm/gc.v b/vm/gc.v
new file mode 100644
index 0000000..95c61a2
--- /dev/null
+++ b/vm/gc.v
@@ -0,0 +1,211 @@
+// gc.v — mark-and-sweep garbage collector for the VuurRaaf VM.
+//
+// The collector runs between opcodes (never mid-instruction, so no live value
+// is ever hidden in a temporary). Roots are the value stack, which also holds
+// every frame's locals (they live at bp+idx). Arrays and structs are traced
+// transitively. The sweep compacts each pool and remaps surviving handles.
+//
+// String constants baked into the bytecode (op_push_s operands) live in
+// strings[0..const_strs] and are never collected; only runtime-allocated
+// strings participate in the cycle.
+module vm
+
+const gc_alloc_trigger = 4096
+
+// collect marks all heap values reachable from the stack, then sweeps and
+// compacts the pools, remapping handles on the stack and inside live
+// containers.
+fn (mut v Vm) collect() {
+	// ---- mark ----
+	mut str_mark := []bool{len: v.strings.len}
+	mut arr_mark := []bool{len: v.arrays.len}
+	mut struct_mark := []bool{len: v.structs.len}
+	mut float_mark := []bool{len: v.floats.len}
+	mut closure_mark := []bool{len: v.closures.len}
+	for i in 0..v.sp {
+		v.mark_value(v.stack[i], mut str_mark, mut arr_mark, mut struct_mark, mut float_mark, mut closure_mark)
+	}
+	// ---- remap tables: old index -> new index (-1 = collected) ----
+	mut str_new := []int{len: v.strings.len, init: -1}
+	mut arr_new := []int{len: v.arrays.len, init: -1}
+	mut struct_new := []int{len: v.structs.len, init: -1}
+	mut float_new := []int{len: v.floats.len, init: -1}
+	mut closure_new := []int{len: v.closures.len, init: -1}
+	mut nstr := v.const_strs
+	for i in v.const_strs..v.strings.len {
+		if str_mark[i] {
+			str_new[i] = nstr
+			nstr++
+		}
+	}
+	mut narr := 0
+	for i in 0..v.arrays.len {
+		if arr_mark[i] {
+			arr_new[i] = narr
+			narr++
+		}
+	}
+	mut nstruct := 0
+	for i in 0..v.structs.len {
+		if struct_mark[i] {
+			struct_new[i] = nstruct
+			nstruct++
+		}
+	}
+	mut nfloat := 0
+	for i in 0..v.floats.len {
+		if float_mark[i] {
+			float_new[i] = nfloat
+			nfloat++
+		}
+	}
+	mut nclosure := 0
+	for i in 0..v.closures.len {
+		if closure_mark[i] {
+			closure_new[i] = nclosure
+			nclosure++
+		}
+	}
+	// ---- rewrite live references ----
+	for i in 0..v.sp {
+		v.stack[i] = v.remap(v.stack[i], str_new, arr_new, struct_new, float_new, closure_new)
+	}
+	for h in 0..v.arrays.len {
+		if arr_mark[h] {
+			for j in 0..v.arrays[h].len {
+				v.arrays[h][j] = v.remap(v.arrays[h][j], str_new, arr_new, struct_new, float_new, closure_new)
+			}
+		}
+	}
+	for h in 0..v.structs.len {
+		if struct_mark[h] {
+			for j in 0..v.structs[h].fields.len {
+				v.structs[h].fields[j].val = v.remap(v.structs[h].fields[j].val, str_new, arr_new, struct_new, float_new, closure_new)
+			}
+		}
+	}
+	// ---- compact pools ----
+	mut strings := v.strings[..v.const_strs]
+	for i in v.const_strs..v.strings.len {
+		if str_mark[i] {
+			strings << v.strings[i]
+		}
+	}
+	v.strings = strings
+	mut arrays := [][]i64{}
+	for i in 0..v.arrays.len {
+		if arr_mark[i] {
+			arrays << v.arrays[i]
+		}
+	}
+	v.arrays = arrays
+	mut structs := []StructVal{}
+	for i in 0..v.structs.len {
+		if struct_mark[i] {
+			structs << v.structs[i]
+		}
+	}
+	v.structs = structs
+	mut floats := []f64{}
+	for i in 0..v.floats.len {
+		if float_mark[i] {
+			floats << v.floats[i]
+		}
+	}
+	v.floats = floats
+	mut closures := []Closure{}
+	for i in 0..v.closures.len {
+		if closure_mark[i] {
+			closures << v.closures[i]
+		}
+	}
+	v.closures = closures
+}
+
+// mark_value traces a value and everything it references using an explicit
+// worklist (arrays of arrays can nest deeply; recursion could overflow).
+fn (mut v Vm) mark_value(x i64, mut str_mark []bool, mut arr_mark []bool, mut struct_mark []bool, mut float_mark []bool, mut closure_mark []bool) {
+	mut work := []i64{}
+	work << x
+	for work.len > 0 {
+		val := work.pop()
+		match v.tag(val) {
+			tag_str {
+				h := v.hand(val)
+				if h >= v.const_strs && h < str_mark.len && !str_mark[h] {
+					str_mark[h] = true
+				}
+			}
+			tag_arr {
+				h := v.hand(val)
+				if h >= 0 && h < arr_mark.len && !arr_mark[h] {
+					arr_mark[h] = true
+					for el in v.arrays[h] {
+						work << el
+					}
+				}
+			}
+			tag_struct {
+				h := v.hand(val)
+				if h >= 0 && h < struct_mark.len && !struct_mark[h] {
+					struct_mark[h] = true
+					for f in v.structs[h].fields {
+						work << f.val
+					}
+				}
+			}
+			tag_float {
+				h := v.hand(val)
+				if h >= 0 && h < float_mark.len && !float_mark[h] {
+					float_mark[h] = true
+				}
+			}
+			tag_closure {
+				h := v.hand(val)
+				if h >= 0 && h < closure_mark.len && !closure_mark[h] {
+					closure_mark[h] = true
+				}
+			}
+			else {}
+		}
+	}
+}
+
+// remap translates a handle to its post-compaction index, leaving integers
+// and uncollected values untouched.
+fn (mut v Vm) remap(x i64, str_new []int, arr_new []int, struct_new []int, float_new []int, closure_new []int) i64 {
+	match v.tag(x) {
+		tag_str {
+			h := v.hand(x)
+			if h >= v.const_strs && h < str_new.len && str_new[h] >= 0 {
+				return v.mkstr(str_new[h])
+			}
+		}
+		tag_arr {
+			h := v.hand(x)
+			if h >= 0 && h < arr_new.len && arr_new[h] >= 0 {
+				return v.mkarr(arr_new[h])
+			}
+		}
+		tag_struct {
+			h := v.hand(x)
+			if h >= 0 && h < struct_new.len && struct_new[h] >= 0 {
+				return v.mkstruct_handle(struct_new[h])
+			}
+		}
+		tag_float {
+			h := v.hand(x)
+			if h >= 0 && h < float_new.len && float_new[h] >= 0 {
+				return v.mkfloat(float_new[h])
+			}
+		}
+		tag_closure {
+			h := v.hand(x)
+			if h >= 0 && h < closure_new.len && closure_new[h] >= 0 {
+				return v.mkclosure(closure_new[h])
+			}
+		}
+		else {}
+	}
+	return x
+}
diff --git a/vm/native.v b/vm/native.v
new file mode 100644
index 0000000..ed09809
--- /dev/null
+++ b/vm/native.v
@@ -0,0 +1,420 @@
+// native.v — host builtins for the VuurRaaf VM.
+//
+// The op_native instruction carries a builtin id and an argument count. Each
+// builtin pops its arguments off the stack (left-to-right push order means the
+// last argument is on top) and pushes a single result (except exit(), which
+// halts the machine). This is where the language touches the host: file I/O,
+// environment, time, randomness, and the math/collection helpers.
+module vm
+
+import os
+import math
+import rand
+import time
+
+fn (mut v Vm) native(id int, _argc int) ! {
+	match id {
+		native_abs {
+			x := v.pop()!
+			if v.is_float(x) {
+				v.push(v.push_float(math.abs(v.fval(x))))!
+			} else {
+				val := v.dec_int(x)
+				v.push(v.enc_int(if val < 0 { -val } else { val }))!
+			}
+		}
+		native_min {
+			b := v.pop()!
+			a := v.pop()!
+			if v.is_float(a) || v.is_float(b) {
+				v.push(v.push_float(math.min(v.to_f64(a), v.to_f64(b))))!
+			} else {
+				x := v.dec_int(a)
+				y := v.dec_int(b)
+				v.push(v.enc_int(if x < y { x } else { y }))!
+			}
+		}
+		native_max {
+			b := v.pop()!
+			a := v.pop()!
+			if v.is_float(a) || v.is_float(b) {
+				v.push(v.push_float(math.max(v.to_f64(a), v.to_f64(b))))!
+			} else {
+				x := v.dec_int(a)
+				y := v.dec_int(b)
+				v.push(v.enc_int(if x > y { x } else { y }))!
+			}
+		}
+		native_pow {
+			b := v.pop()!
+			a := v.pop()!
+			v.push(v.push_float(math.pow(v.to_f64(a), v.to_f64(b))))!
+		}
+		native_sqrt {
+			x := v.pop()!
+			v.push(v.push_float(math.sqrt(v.to_f64(x))))!
+		}
+		native_floor {
+			x := v.pop()!
+			v.push(v.enc_int(i64(math.floor(v.to_f64(x)))))!
+		}
+		native_ceil {
+			x := v.pop()!
+			v.push(v.enc_int(i64(math.ceil(v.to_f64(x)))))!
+		}
+		native_round {
+			x := v.pop()!
+			v.push(v.enc_int(i64(math.round(v.to_f64(x)))))!
+		}
+		native_rand {
+			v.push(v.push_float(rand.f64()))!
+		}
+		native_rand_int {
+			n := int(v.dec_int(v.pop()!))
+			if n <= 0 {
+				return error('rand_int() expects a positive bound')
+			}
+			v.push(v.enc_int(i64(rand.intn(n) or { return error('rand_int() failed') })))!
+		}
+		native_int {
+			x := v.pop()!
+			if v.is_str(x) && v.valid_handle(x) {
+				v.push(v.enc_int(i64(v.strings[v.hand(x)].i64())))!
+			} else if v.is_float(x) {
+				v.push(v.enc_int(i64(v.fval(x))))!
+			} else if v.is_arr(x) || v.is_struct(x) {
+				return error('cannot convert a ${v.type_name(x)} to int')
+			} else {
+				v.push(x)!
+			}
+		}
+		native_str {
+			x := v.pop()!
+			v.push(v.alloc_str(v.val_str(x, 0)))!
+		}
+		native_float {
+			x := v.pop()!
+			if v.is_str(x) && v.valid_handle(x) {
+				v.push(v.push_float(v.strings[v.hand(x)].f64()))!
+			} else if v.is_float(x) {
+				v.push(x)!
+			} else if v.is_arr(x) || v.is_struct(x) {
+				return error('cannot convert a ${v.type_name(x)} to float')
+			} else {
+				v.push(v.push_float(f64(v.dec_int(x))))!
+			}
+		}
+		native_type {
+			x := v.pop()!
+			v.push(v.alloc_str(v.type_name(x)))!
+		}
+		native_split {
+			delim := v.pop_str()!
+			s := v.pop_str()!
+			parts := s.split(delim)
+			mut arr := []i64{}
+			for p in parts {
+				v.strings << p
+				arr << v.mkstr(v.strings.len - 1)
+			}
+			v.arrays << arr
+			v.push(v.mkarr(v.arrays.len - 1))!
+		}
+		native_join {
+			delim := v.pop_str()!
+			h := v.pop()!
+			if !v.is_arr(h) || !v.valid_arr_handle(h) {
+				return error('join() expects an array as its first argument')
+			}
+			a := v.arrays[v.hand(h)]
+			mut parts := []string{}
+			for x in a {
+				if v.is_str(x) && v.valid_handle(x) {
+					parts << v.strings[v.hand(x)]
+				} else {
+					parts << v.val_str(x, 0)
+				}
+			}
+			v.push(v.alloc_str(parts.join(delim)))!
+		}
+		native_contains {
+			sub := v.pop_str()!
+			s := v.pop_str()!
+			v.push(v.enc_int(bool_i64(s.contains(sub))))!
+		}
+		native_starts_with {
+			sub := v.pop_str()!
+			s := v.pop_str()!
+			v.push(v.enc_int(bool_i64(s.starts_with(sub))))!
+		}
+		native_ends_with {
+			sub := v.pop_str()!
+			s := v.pop_str()!
+			v.push(v.enc_int(bool_i64(s.ends_with(sub))))!
+		}
+		native_trim {
+			s := v.pop_str()!
+			v.push(v.alloc_str(s.trim_space()))!
+		}
+		native_lower {
+			s := v.pop_str()!
+			v.push(v.alloc_str(s.to_lower()))!
+		}
+		native_upper {
+			s := v.pop_str()!
+			v.push(v.alloc_str(s.to_upper()))!
+		}
+		native_pop {
+			h := v.pop()!
+			if !v.is_arr(h) || !v.valid_arr_handle(h) {
+				return error('pop() expects an array')
+			}
+			mut a := v.arrays[v.hand(h)]
+			if a.len == 0 {
+				return error('pop() on an empty array')
+			}
+			val := a[a.len - 1]
+			v.arrays[v.hand(h)] = a[..a.len - 1]
+			v.push(val)!
+		}
+		native_insert {
+			val := v.pop()!
+			idx := int(v.dec_int(v.pop()!))
+			h := v.pop()!
+			if !v.is_arr(h) || !v.valid_arr_handle(h) {
+				return error('insert() expects an array as its first argument')
+			}
+			a := v.arrays[v.hand(h)]
+			if idx < 0 || idx > a.len {
+				return error('insert index ${idx} out of bounds (len ${a.len})')
+			}
+			mut na := []i64{}
+			for i, x in a {
+				if i == idx {
+					na << val
+				}
+				na << x
+			}
+			if idx == a.len {
+				na << val
+			}
+			v.arrays[v.hand(h)] = na
+			v.push(h)!
+		}
+		native_remove {
+			idx := int(v.dec_int(v.pop()!))
+			h := v.pop()!
+			if !v.is_arr(h) || !v.valid_arr_handle(h) {
+				return error('remove() expects an array as its first argument')
+			}
+			a := v.arrays[v.hand(h)]
+			if idx < 0 || idx >= a.len {
+				return error('remove index ${idx} out of bounds (len ${a.len})')
+			}
+			mut na := []i64{}
+			for i, x in a {
+				if i != idx {
+					na << x
+				}
+			}
+			v.arrays[v.hand(h)] = na
+			v.push(h)!
+		}
+		native_sort {
+			h := v.pop()!
+			if !v.is_arr(h) || !v.valid_arr_handle(h) {
+				return error('sort() expects an array')
+			}
+			mut a := v.arrays[v.hand(h)]
+			// insertion sort by numeric value
+			for i in 1..a.len {
+				key := a[i]
+				mut j := i - 1
+				for j >= 0 && v.num_gt(a[j], key) {
+					a[j + 1] = a[j]
+					j--
+				}
+				a[j + 1] = key
+			}
+			v.push(h)!
+		}
+		native_clone {
+			x := v.pop()!
+			if v.is_arr(x) && v.valid_arr_handle(x) {
+				v.arrays << v.arrays[v.hand(x)].clone()
+				v.push(v.mkarr(v.arrays.len - 1))!
+			} else if v.is_struct(x) && v.valid_struct_handle(x) {
+				s := v.structs[v.hand(x)]
+				v.structs << StructVal{ fields: s.fields.clone() }
+				v.push(v.mkstruct_handle(v.structs.len - 1))!
+			} else if v.is_str(x) && v.valid_handle(x) {
+				v.push(v.alloc_str(v.strings[v.hand(x)]))!
+			} else if v.is_float(x) {
+				v.push(v.push_float(v.fval(x)))!
+			} else {
+				v.push(x)!
+			}
+		}
+		native_reverse {
+			h := v.pop()!
+			if !v.is_arr(h) || !v.valid_arr_handle(h) {
+				return error('reverse() expects an array')
+			}
+			mut a := v.arrays[v.hand(h)]
+			for i in 0..a.len / 2 {
+				a[i], a[a.len - 1 - i] = a[a.len - 1 - i], a[i]
+			}
+			v.push(h)!
+		}
+		native_index_of {
+			val := v.pop()!
+			h := v.pop()!
+			if v.is_arr(h) && v.valid_arr_handle(h) {
+				a := v.arrays[v.hand(h)]
+				for i, x in a {
+					if v.cmp(x, val, '==')! == 1 {
+						v.push(v.enc_int(i64(i)))!
+						return
+					}
+				}
+				v.push(v.enc_int(-1))!
+				return
+			}
+			if v.is_str(h) && v.valid_handle(h) {
+				if !v.is_str(val) || !v.valid_handle(val) {
+					return error('index_of() on a string expects a string needle')
+				}
+				s := v.strings[v.hand(h)]
+				needle := v.strings[v.hand(val)]
+				byte_idx := s.index(needle) or { -1 }
+				if byte_idx < 0 {
+					v.push(v.enc_int(-1))!
+					return
+				}
+				// convert byte offset to a rune index so UTF-8 strings count characters
+				rune_idx := s[..byte_idx].runes().len
+				v.push(v.enc_int(i64(rune_idx)))!
+				return
+			}
+			return error('index_of() expects an array or string as its first argument')
+		}
+		native_args {
+			mut arr := []i64{}
+			for s in v.prog_args {
+				v.strings << s
+				arr << v.mkstr(v.strings.len - 1)
+			}
+			v.arrays << arr
+			v.push(v.mkarr(v.arrays.len - 1))!
+		}
+		native_getenv {
+			name := v.pop_str()!
+			v.push(v.alloc_str(os.getenv(name)))!
+		}
+		native_setenv {
+			val := v.pop_str()!
+			name := v.pop_str()!
+			os.setenv(name, val, true)
+			v.push(v.enc_int(0))!
+		}
+		native_exit {
+			code := int(v.dec_int(v.pop()!))
+			v.exit_code = i64(code)
+			v.did_exit = true
+			v.halted = true
+		}
+		native_time {
+			v.push(v.push_float(f64(time.now().unix_milli()) / 1000.0))!
+		}
+		native_sleep {
+			ms := int(v.dec_int(v.pop()!))
+			time.sleep(time.Duration(ms) * time.millisecond)
+			v.push(v.enc_int(0))!
+		}
+		native_read_file {
+			path := v.pop_str()!
+			content := os.read_file(path) or { return error('cannot read file "${path}": ${err}') }
+			v.push(v.alloc_str(content))!
+		}
+		native_write_file {
+			content := v.pop_str()!
+			path := v.pop_str()!
+			os.write_file(path, content) or { return error('cannot write file "${path}": ${err}') }
+			v.push(v.enc_int(0))!
+		}
+		native_eprint {
+			x := v.pop()!
+			eprintln(v.val_str(x, 0))
+		}
+		else {
+			return error('unknown native builtin ${id}')
+		}
+	}
+}
+
+// pop_str pops the top value and requires it to be a string.
+fn (mut v Vm) pop_str() !string {
+	x := v.pop()!
+	if !v.is_str(x) || !v.valid_handle(x) {
+		return error('expected a string argument')
+	}
+	return v.strings[v.hand(x)]
+}
+
+// type_name returns the type label of a tagged value.
+fn (mut v Vm) type_name(x i64) string {
+	if v.is_str(x) {
+		return 'string'
+	}
+	if v.is_float(x) {
+		return 'float'
+	}
+	if v.is_arr(x) {
+		return 'array'
+	}
+	if v.is_struct(x) {
+		return 'struct'
+	}
+	return 'int'
+}
+
+// str_method dispatches a string method call. The receiver was pushed before
+// the arguments, so it is the first argument from the native builtin's point
+// of view; delegating keeps the behavior identical to the free-function forms.
+fn (mut v Vm) str_method(name string, argc int) ! {
+	bid := match name {
+		'to_upper' { native_upper }
+		'to_lower' { native_lower }
+		'trim' { native_trim }
+		'contains' { native_contains }
+		'starts_with' { native_starts_with }
+		'ends_with' { native_ends_with }
+		'split' { native_split }
+		'index_of' { native_index_of }
+		'to_int' { native_int }
+		'to_float' { native_float }
+		else { -1 }
+	}
+	if bid >= 0 {
+		// native builtins pop the first argument (the receiver) last
+		v.native(bid, argc + 1)!
+		return
+	}
+	if name == 'len' {
+		h := v.pop()!
+		if !v.is_str(h) || !v.valid_handle(h) {
+			return error('len() on a non-string value')
+		}
+		v.push(v.enc_int(i64(v.strings[v.hand(h)].runes().len)))!
+		return
+	}
+	return error('unknown string method "${name}"')
+}
+
+// num_gt compares two values by their numeric value (int or float).
+fn (mut v Vm) num_gt(x i64, y i64) bool {
+	if v.is_float(x) || v.is_float(y) {
+		return v.to_f64(x) > v.to_f64(y)
+	}
+	return v.dec_int(x) > v.dec_int(y)
+}
diff --git a/vm/opcodes.v b/vm/opcodes.v
index ecbeccd..1836d39 100644
--- a/vm/opcodes.v
+++ b/vm/opcodes.v
@@ -47,3 +47,61 @@ const op_shas = u8(40) // has(map, "key") -> 1 if key exists, 0 otherwise
 const op_sdel = u8(41) // delete(map, "key") -> removes the key
 const op_slen = u8(42) // slen(struct) -> number of fields
 const op_skeys = u8(43) // skeys(struct) -> array of field name strings
+const op_slice = u8(44) // slice(arr/str, start, end) -> sliced arr/str
+const op_push_f = u8(45) // push a float literal (8-byte little-endian f64)
+const op_native = u8(46) // call a host builtin: <id:i64> <argc:i64>
+const op_and_b = u8(47) // bitwise AND
+const op_or_b = u8(48) // bitwise OR
+const op_xor = u8(49) // bitwise XOR
+const op_shl = u8(50) // shift left
+const op_shr = u8(51) // shift right
+const op_not_b = u8(52) // bitwise NOT
+const op_try = u8(53) // push handler: <catch_ip:i64>
+const op_throw = u8(54) // throw: pop error, unwind to nearest handler, push error
+const op_catch_done = u8(55) // pop handler (normal completion)
+const op_closure = u8(56) // push closure: <entry:i64>
+const op_call_closure = u8(57) // call closure: <argc:i64>
+const op_argc = u8(58) // push the current frame's arg count
+const op_load_dyn = u8(59) // pop idx, push stack[bp + idx]
+const op_varargs = u8(60) // <named:i64> <dst:i64> — collect args[named..argc-1] into array at local dst
+const op_str_method = u8(61) // <name:str> <argc:i64> — call a string method (s.len(), s.contains(x), ...)
+
+// native builtin ids (the operand to op_native)
+const native_abs = 100
+const native_min = 101
+const native_max = 102
+const native_pow = 103
+const native_sqrt = 104
+const native_floor = 105
+const native_ceil = 106
+const native_round = 107
+const native_rand = 108
+const native_rand_int = 109
+const native_int = 110
+const native_str = 111
+const native_float = 112
+const native_type = 113
+const native_split = 114
+const native_join = 115
+const native_contains = 116
+const native_starts_with = 117
+const native_ends_with = 118
+const native_trim = 119
+const native_lower = 120
+const native_upper = 121
+const native_pop = 122
+const native_insert = 123
+const native_remove = 124
+const native_sort = 125
+const native_clone = 126
+const native_reverse = 127
+const native_index_of = 128
+const native_args = 129
+const native_getenv = 130
+const native_setenv = 131
+const native_exit = 132
+const native_time = 133
+const native_sleep = 134
+const native_read_file = 135
+const native_write_file = 136
+const native_eprint = 137
diff --git a/vm/ops.v b/vm/ops.v
index e3e3b61..1206f4d 100644
--- a/vm/ops.v
+++ b/vm/ops.v
@@ -1,6 +1,8 @@
 // ops.v — arithmetic, comparison, and string operations for the VuurRaaf VM.
 module vm
 
+import math
+
 fn (mut v Vm) add(a i64, b i64) !i64 {
 	if v.is_arr(a) || v.is_arr(b) {
 		return error('cannot add arrays with +')
@@ -17,18 +19,61 @@ fn (mut v Vm) add(a i64, b i64) !i64 {
 	if v.is_str(b) {
 		return v.alloc_str(v.num_str(a) + v.strings[v.hand(b)])
 	}
+	if v.is_float(a) || v.is_float(b) {
+		return v.push_float(v.to_f64(a) + v.to_f64(b))
+	}
 	return v.enc_int(v.dec_int(a) + v.dec_int(b))
 }
 
+// to_f64 promotes an integer or float tagged value to f64.
+fn (mut v Vm) to_f64(x i64) f64 {
+	if v.is_float(x) {
+		return v.fval(x)
+	}
+	return f64(v.dec_int(x))
+}
+
 fn (mut v Vm) alloc_str(s string) i64 {
 	v.strings << s
 	return v.mkstr(v.strings.len - 1)
 }
 
 fn (mut v Vm) num_str(x i64) string {
+	if v.is_float(x) {
+		return fmt_float(v.fval(x))
+	}
 	return v.dec_int(x).str()
 }
 
+// fmt_float renders an f64 nicely: integral values lose the trailing ".0",
+// -0 collapses to 0, and most floats avoid V's default scientific notation.
+fn fmt_float(f f64) string {
+	if f == 0.0 {
+		return '0'
+	}
+	if math.is_nan(f) {
+		return 'NaN'
+	}
+	if math.is_inf(f, 1) {
+		return 'Inf'
+	}
+	if math.is_inf(f, -1) {
+		return '-Inf'
+	}
+	if f == math.floor(f) && math.abs(f) < 1e18 {
+		return i64(f).str()
+	}
+	if math.abs(f) < 1e18 {
+		mut s := '${f:.14f}'
+		s = s.trim_right('0').trim_right('.')
+		if s == '' {
+			return '0'
+		}
+		return s
+	}
+	return f.str()
+}
+
 fn (mut v Vm) arith(a i64, b i64, op string) !i64 {
 	if v.is_str(a) || v.is_str(b) {
 		return error('cannot use strings with "${op}"')
@@ -39,6 +84,33 @@ fn (mut v Vm) arith(a i64, b i64, op string) !i64 {
 	if v.is_struct(a) || v.is_struct(b) {
 		return error('cannot use structs with "${op}"')
 	}
+	if v.is_float(a) || v.is_float(b) {
+		x := v.to_f64(a)
+		y := v.to_f64(b)
+		match op {
+			'-' {
+				return v.push_float(x - y)
+			}
+			'*' {
+				return v.push_float(x * y)
+			}
+			'/' {
+				if y == 0.0 {
+					return error('division by zero')
+				}
+				return v.push_float(x / y)
+			}
+			'%' {
+				if y == 0.0 {
+					return error('division by zero')
+				}
+				return v.push_float(math.fmod(x, y))
+			}
+			else {
+				return error('internal: bad arith op "${op}"')
+			}
+		}
+	}
 	x := v.dec_int(a)
 	y := v.dec_int(b)
 	match op {
@@ -97,6 +169,19 @@ fn (mut v Vm) cmp(a i64, b i64, op string) !i64 {
 	if v.is_str(a) || v.is_str(b) {
 		return error('cannot compare a string and a number')
 	}
+	if v.is_float(a) || v.is_float(b) {
+		x := v.to_f64(a)
+		y := v.to_f64(b)
+		return bool_i64(match op {
+			'==' { x == y }
+			'!=' { x != y }
+			'<' { x < y }
+			'<=' { x <= y }
+			'>' { x > y }
+			'>=' { x >= y }
+			else { return error('internal: bad cmp op "${op}"') }
+		})
+	}
 	x := v.dec_int(a)
 	y := v.dec_int(b)
 	return bool_i64(match op {
diff --git a/vm/print.v b/vm/print.v
index 1f92f03..aa322c5 100644
--- a/vm/print.v
+++ b/vm/print.v
@@ -44,6 +44,12 @@ fn (mut v Vm) val_str(x i64, depth int) string {
 		}
 		return out + '}'
 	}
+	if v.is_float(x) && v.valid_float_handle(x) {
+		return fmt_float(v.fval(x))
+	}
+	if v.is_closure(x) && v.valid_closure_handle(x) {
+		return '<fn@${v.closures[v.hand(x)].entry}>'
+	}
 	return v.dec_int(x).str()
 }
 
@@ -52,6 +58,7 @@ fn (mut v Vm) trace_op(op u8) {
 		op_halt { 'halt' }
 		op_push_i { 'push_int' }
 		op_push_s { 'push_str' }
+		op_push_f { 'push_float' }
 		op_load { 'load' }
 		op_store { 'store' }
 		op_pop { 'pop' }
@@ -93,6 +100,23 @@ fn (mut v Vm) trace_op(op u8) {
 		op_sdel { 'sdel' }
 		op_slen { 'slen' }
 		op_skeys { 'skeys' }
+		op_slice { 'slice' }
+		op_native { 'native' }
+		op_and_b { 'and_b' }
+		op_or_b { 'or_b' }
+		op_xor { 'xor' }
+		op_shl { 'shl' }
+		op_shr { 'shr' }
+		op_not_b { 'not_b' }
+		op_try { 'try' }
+		op_throw { 'throw' }
+		op_catch_done { 'catch_done' }
+		op_closure { 'closure' }
+		op_call_closure { 'call_closure' }
+		op_argc { 'argc' }
+		op_load_dyn { 'load_dyn' }
+		op_varargs { 'varargs' }
+		op_str_method { 'str_method' }
 		else { '??' }
 	}
 	mut s := ''
@@ -100,10 +124,13 @@ fn (mut v Vm) trace_op(op u8) {
 		if i > 0 {
 			s += ' '
 		}
-		if v.is_str(v.stack[i]) && v.valid_handle(v.stack[i]) {
-			s += '"${v.strings[v.hand(v.stack[i])]}"'
+		x := v.stack[i]
+		if v.is_str(x) && v.valid_handle(x) {
+			s += '"${v.strings[v.hand(x)]}"'
+		} else if v.is_closure(x) {
+			s += '<fn>'
 		} else {
-			s += v.val_str(v.stack[i], 0)
+			s += v.val_str(x, 0)
 		}
 	}
 	println('  [ip=${v.ip:4}] ${name:-9}  stack: [${s}]')
diff --git a/vm/types.v b/vm/types.v
index 1741078..19d85de 100644
--- a/vm/types.v
+++ b/vm/types.v
@@ -1,6 +1,8 @@
 // types.v — core types and constants for the VuurRaaf VM.
 module vm
 
+import obj
+
 const stack_cap = 65536
 
 // Field is one `name: value` entry of a struct value.
@@ -15,18 +17,38 @@ mut:
 	fields []Field
 }
 
+// Handler records a try/catch handler pushed at runtime.
+struct Closure {
+	entry int // code IP of the function body
+}
+
+struct Handler {
+	ip int // catch_ip
+	bp int // frame base at try point
+	sp int // stack pointer right after the handler record
+}
+
 struct Vm {
 mut:
-	code    []u8
-	strings []string
-	arrays  [][]i64
-	structs []StructVal
-	stack   []i64
-	sp      int
-	bp      int
-	ip      int
-	trace   bool
-	halted  bool
+	code      []u8
+	strings   []string
+	arrays    [][]i64
+	structs   []StructVal
+	floats    []f64
+	closures  []Closure
+	stack     []i64
+	sp        int
+	bp        int
+	ip        int
+	trace     bool
+	halted    bool
+	prog_args []string
+	exit_code i64
+	did_exit  bool
+	handlers  []Handler
+	lines     []obj.LineInfo // debug info: code offset -> source line
+	const_strs int          // strings[0..const_strs] are bytecode constants, never collected
+	last_heap  int          // heap size at the last GC check (allocation trigger)
 }
 
 fn bool_i64(b bool) i64 {
diff --git a/vm/value.v b/vm/value.v
index f09b8c0..428af6b 100644
--- a/vm/value.v
+++ b/vm/value.v
@@ -1,49 +1,101 @@
 // value.v — tagged value encoding and helpers for the VuurRaaf VM.
 //
-// Stack values are 64-bit tagged integers with two tag bits:
-//   low bits 00  -> encoded number  (value = raw << 2)
-//   low bits 01  -> string handle   (handle = value >> 2, into v.strings)
-//   low bits 10  -> struct handle   (handle = value >> 2, into v.structs)
-//   low bits 11  -> array handle    (handle = value >> 2, into v.arrays)
+// Stack values are 64-bit tagged integers with three tag bits:
+//   low bits 000 -> encoded integer (value = raw << 3)
+//   low bits 001 -> string handle   (handle = value >> 3, into v.strings)
+//   low bits 010 -> struct handle   (handle = value >> 3, into v.structs)
+//   low bits 011 -> array handle    (handle = value >> 3, into v.arrays)
+//   low bits 100 -> float handle    (handle = value >> 3, into v.floats)
 module vm
 
-fn (mut v Vm) is_str(x i64) bool {
-	return x & 3 == 1
+const tag_mask = u64(7)
+const tag_int = u64(0)
+const tag_str = u64(1)
+const tag_struct = u64(2)
+const tag_arr = u64(3)
+const tag_float = u64(4)
+const tag_closure = u64(5)
+
+fn (mut v Vm) tag(x i64) u64 {
+	return u64(x) & tag_mask
 }
 
-fn (mut v Vm) is_arr(x i64) bool {
-	return x & 3 == 3
+fn (mut v Vm) is_int(x i64) bool {
+	return u64(x) & tag_mask == tag_int
+}
+
+fn (mut v Vm) is_str(x i64) bool {
+	return u64(x) & tag_mask == tag_str
 }
 
 fn (mut v Vm) is_struct(x i64) bool {
-	return x & 3 == 2
+	return u64(x) & tag_mask == tag_struct
+}
+
+fn (mut v Vm) is_arr(x i64) bool {
+	return u64(x) & tag_mask == tag_arr
+}
+
+fn (mut v Vm) is_float(x i64) bool {
+	return u64(x) & tag_mask == tag_float
+}
+
+fn (mut v Vm) is_closure(x i64) bool {
+	return u64(x) & tag_mask == tag_closure
+}
+
+// is_num reports whether x is an integer (tag 0). Floats are a distinct type.
+fn (mut v Vm) is_num(x i64) bool {
+	return u64(x) & tag_mask == tag_int
 }
 
 fn (mut v Vm) enc_int(x i64) i64 {
-	return u64(x) << 2
+	return i64(u64(x) << 3)
 }
 
 fn (mut v Vm) dec_int(x i64) i64 {
-	return x >> 2
+	return x >> 3
 }
 
 fn (mut v Vm) hand(x i64) int {
-	return int(x >> 2)
+	return int(x >> 3)
 }
 
 fn (mut v Vm) mkstr(idx int) i64 {
-	return (u64(idx) << 2) | 1
+	return i64((u64(idx) << 3) | tag_str)
 }
 
 fn (mut v Vm) mkarr(idx int) i64 {
-	return (u64(idx) << 2) | 3
+	return i64((u64(idx) << 3) | tag_arr)
 }
 
 fn (mut v Vm) mkstruct_handle(idx int) i64 {
-	return (u64(idx) << 2) | 2
+	return i64((u64(idx) << 3) | tag_struct)
+}
+
+fn (mut v Vm) mkfloat(idx int) i64 {
+	return i64((u64(idx) << 3) | tag_float)
+}
+
+fn (mut v Vm) mkclosure(idx int) i64 {
+	return i64((u64(idx) << 3) | tag_closure)
+}
+
+// push_float interns a float into the pool and returns its tagged handle.
+fn (mut v Vm) push_float(f f64) i64 {
+	v.floats << f
+	return v.mkfloat(v.floats.len - 1)
+}
+
+// fval returns the f64 value of a float handle.
+fn (mut v Vm) fval(x i64) f64 {
+	return v.floats[v.hand(x)]
 }
 
 fn (mut v Vm) truthy(x i64) bool {
+	if v.is_float(x) {
+		return v.fval(x) != 0.0
+	}
 	return x != 0
 }
 
@@ -61,3 +113,25 @@ fn (mut v Vm) valid_struct_handle(x i64) bool {
 	h := v.hand(x)
 	return h >= 0 && h < v.structs.len
 }
+
+fn (mut v Vm) valid_float_handle(x i64) bool {
+	h := v.hand(x)
+	return h >= 0 && h < v.floats.len
+}
+
+fn (mut v Vm) valid_closure_handle(x i64) bool {
+	h := v.hand(x)
+	return h >= 0 && h < v.closures.len
+}
+
+// valid_handle_for bounds-checks a handle against the pool matching its tag.
+fn (mut v Vm) valid_handle_for(x i64) bool {
+	return match v.tag(x) {
+		tag_str { v.valid_handle(x) }
+		tag_struct { v.valid_struct_handle(x) }
+		tag_arr { v.valid_arr_handle(x) }
+		tag_float { v.valid_float_handle(x) }
+		tag_closure { v.valid_closure_handle(x) }
+		else { true }
+	}
+}
diff --git a/vm/vm.v b/vm/vm.v
index ecfe963..837bfea 100644
--- a/vm/vm.v
+++ b/vm/vm.v
@@ -6,15 +6,25 @@
 module vm
 
 import obj
+import math
 
 // run executes the function named `entry` from the executable `bin` and
 // returns its return value (0 if it never returns one).
 pub fn run(bin obj.Bin, entry string, trace bool) !i64 {
+	return run_with_args(bin, entry, trace, []string{})
+}
+
+// run_with_args is run() with command-line arguments exposed to the program
+// via the `args()` builtin.
+pub fn run_with_args(bin obj.Bin, entry string, trace bool, args []string) !i64 {
 	mut v := Vm{
-		code:    bin.code
-		strings: bin.strings.clone()
-		stack:   []i64{len: stack_cap}
-		trace:   trace
+		code:       bin.code
+		strings:    bin.strings.clone()
+		stack:      []i64{len: stack_cap}
+		trace:      trace
+		prog_args:  args
+		lines:      bin.lines
+		const_strs: bin.strings.len
 	}
 	mut entry_ip := -1
 	for f in bin.fns {
@@ -38,15 +48,43 @@ pub fn run(bin obj.Bin, entry string, trace bool) !i64 {
 	v.sp++
 	v.bp = v.sp
 	v.ip = entry_ip
-	v.exec()!
+	v.exec() or {
+		return error('${err.msg()} at ${v.where()}')
+	}
+	if v.did_exit {
+		return v.exit_code
+	}
 	if v.sp > 0 {
 		return v.dec_int(v.stack[0])
 	}
 	return 0
 }
 
+// where returns a source-level location for the current instruction pointer:
+// `line 12 (ip 345)` when debug info is available, otherwise just `(ip 345)`.
+fn (v Vm) where() string {
+	// line table entries are recorded in code order, so walk backwards from
+	// the most recent entry to find the last one at or before v.ip
+	for i := v.lines.len - 1; i >= 0; i-- {
+		if v.ip >= int(v.lines[i].off) {
+			return 'line ${v.lines[i].line} (ip ${v.ip})'
+		}
+	}
+	return '(ip ${v.ip})'
+}
+
 fn (mut v Vm) exec() ! {
 	for !v.halted {
+		// garbage collection: runs between opcodes when the heap has grown by
+		// gc_alloc_trigger entries since the last collection, so no live value
+		// is ever mid-flight in an instruction handler
+		heap := v.strings.len + v.arrays.len + v.structs.len + v.floats.len + v.closures.len
+		if heap > v.last_heap + gc_alloc_trigger {
+			v.collect()
+			v.last_heap = v.strings.len + v.arrays.len + v.structs.len + v.floats.len + v.closures.len
+		} else {
+			v.last_heap = heap
+		}
 		op := v.code[v.ip]
 		if v.trace {
 			v.trace_op(op)
@@ -64,6 +102,11 @@ fn (mut v Vm) exec() ! {
 				idx := int(v.read_i64())
 				v.push(v.mkstr(idx))!
 			}
+			op_push_f {
+				v.ip++
+				f := v.read_f64()
+				v.push(v.push_float(f))!
+			}
 			op_load {
 				v.ip++
 				idx := int(v.read_i64())
@@ -117,16 +160,17 @@ fn (mut v Vm) exec() ! {
 			op_neg {
 				v.ip++
 				a := v.pop()!
-				if v.is_str(a) {
+				if v.is_float(a) {
+					v.push(v.push_float(-v.fval(a)))!
+				} else if v.is_str(a) {
 					return error('cannot negate a string')
-				}
-				if v.is_arr(a) {
+				} else if v.is_arr(a) {
 					return error('cannot negate an array')
-				}
-				if v.is_struct(a) {
+				} else if v.is_struct(a) {
 					return error('cannot negate a struct')
+				} else {
+					v.push(v.enc_int(-v.dec_int(a)))!
 				}
-				v.push(v.enc_int(-v.dec_int(a)))!
 			}
 			op_eq {
 				v.ip++
@@ -247,14 +291,22 @@ fn (mut v Vm) exec() ! {
 				v.ip++
 				idx := int(v.dec_int(v.pop()!))
 				h := v.pop()!
-				if !v.is_arr(h) || !v.valid_arr_handle(h) {
-					return error('indexing a non-array value')
+				if v.is_arr(h) && v.valid_arr_handle(h) {
+					a := v.arrays[v.hand(h)]
+					if idx < 0 || idx >= a.len {
+						return error('array index ${idx} out of bounds (len ${a.len})')
+					}
+					v.push(a[idx])!
+				} else if v.is_str(h) && v.valid_handle(h) {
+					// rune-based string indexing: s[i] is the i-th character
+					runes := v.strings[v.hand(h)].runes()
+					if idx < 0 || idx >= runes.len {
+						return error('string index ${idx} out of bounds (len ${runes.len})')
+					}
+					v.push(v.alloc_str(runes[idx].str()))!
+				} else {
+					return error('indexing a non-array, non-string value')
 				}
-				a := v.arrays[v.hand(h)]
-				if idx < 0 || idx >= a.len {
-					return error('array index ${idx} out of bounds (len ${a.len})')
-				}
-				v.push(a[idx])!
 			}
 			op_aset {
 				v.ip++
@@ -276,8 +328,10 @@ fn (mut v Vm) exec() ! {
 					v.push(v.enc_int(i64(v.arrays[v.hand(h)].len)))!
 				} else if v.is_struct(h) && v.valid_struct_handle(h) {
 					v.push(v.enc_int(i64(v.structs[v.hand(h)].fields.len)))!
+				} else if v.is_str(h) && v.valid_handle(h) {
+					v.push(v.enc_int(i64(v.strings[v.hand(h)].runes().len)))!
 				} else {
-					return error('len() on a non-array, non-struct value')
+					return error('len() on a non-array, non-struct, non-string value')
 				}
 			}
 			op_apush {
@@ -370,6 +424,139 @@ fn (mut v Vm) exec() ! {
 			op_skeys {
 				v.op_skeys()!
 			}
+			op_slice {
+				v.op_slice()!
+			}
+			op_native {
+				v.ip++
+				id := int(v.read_i64())
+				argc := int(v.read_i64())
+				v.native(id, argc)!
+			}
+			op_and_b {
+				v.ip++
+				b := v.pop()!
+				a := v.pop()!
+				v.push(v.enc_int(v.dec_int(a) & v.dec_int(b)))!
+			}
+			op_or_b {
+				v.ip++
+				b := v.pop()!
+				a := v.pop()!
+				v.push(v.enc_int(v.dec_int(a) | v.dec_int(b)))!
+			}
+			op_xor {
+				v.ip++
+				b := v.pop()!
+				a := v.pop()!
+				v.push(v.enc_int(v.dec_int(a) ^ v.dec_int(b)))!
+			}
+			op_shl {
+				v.ip++
+				b := v.pop()!
+				a := v.pop()!
+				x := v.dec_int(a)
+				y := u32(v.dec_int(b))
+				v.push(v.enc_int(x << y))!
+			}
+			op_shr {
+				v.ip++
+				b := v.pop()!
+				a := v.pop()!
+				x := v.dec_int(a)
+				y := u32(v.dec_int(b))
+				v.push(v.enc_int(x >> y))!
+			}
+			op_not_b {
+				v.ip++
+				a := v.pop()!
+				v.push(v.enc_int(~v.dec_int(a)))!
+			}
+			op_try {
+				v.ip++
+				catch_ip := int(v.read_i64())
+				v.handlers << Handler{ ip: catch_ip, bp: v.bp, sp: v.sp }
+			}
+			op_throw {
+				v.ip++
+				err_val := v.pop()!
+				if v.handlers.len == 0 {
+					return error('unhandled throw: ${v.val_str(err_val, 0)}')
+				}
+				h := v.handlers[v.handlers.len - 1]
+				v.handlers.delete_last()
+				v.bp = h.bp
+				v.sp = h.sp
+				v.push(err_val)!
+				v.ip = h.ip
+			}
+			op_catch_done {
+				v.ip++
+				if v.handlers.len > 0 {
+					v.handlers.delete_last()
+				}
+			}
+			op_closure {
+				v.ip++
+				entry := int(v.read_i64())
+				v.closures << Closure{ entry: entry }
+				v.push(v.mkclosure(v.closures.len - 1))!
+			}
+			op_call_closure {
+				v.ip++
+				argc := int(v.read_i64())
+				// stack: [...closure, arg_0, ..., arg_{argc-1}]
+				h := v.stack[v.sp - argc - 1]
+				if !v.is_closure(h) || !v.valid_closure_handle(h) {
+					return error('cannot call a non-function value')
+				}
+				entry := v.closures[v.hand(h)].entry
+				// Shift args left to overwrite the closure slot, then
+				// insert a return-value placeholder so the callee's
+				// retv never overwrites the caller's local that held
+				// the closure handle.
+				for i := 0; i < argc; i++ {
+					v.stack[v.sp - argc - 1 + i] = v.stack[v.sp - argc + i]
+				}
+				v.stack[v.sp - 1] = v.enc_int(0) // return-value placeholder
+				v.sp-- // closure was removed; unwind one slot
+				v.call(entry, argc)
+			}
+			op_argc {
+				v.ip++
+				argc := v.dec_int(v.stack[v.bp - 1])
+				v.push(v.enc_int(argc))!
+			}
+			op_load_dyn {
+				v.ip++
+				idx := int(v.dec_int(v.pop()!))
+				if v.bp + idx < 0 || v.bp + idx >= v.sp {
+					return error('dynamic load index ${idx} out of range')
+				}
+				v.push(v.stack[v.bp + idx])!
+			}
+			op_varargs {
+				v.ip++
+				named := int(v.read_i64())
+				dst := int(v.read_i64())
+				argc := int(v.dec_int(v.stack[v.bp - 1]))
+				mut n := argc - named
+				if n < 0 {
+					n = 0
+				}
+				mut arr := []i64{len: n}
+				for i in 0..n {
+					arr[i] = v.stack[v.bp + named + i]
+				}
+				v.arrays << arr
+				v.stack[v.bp + dst] = v.mkarr(v.arrays.len - 1)
+			}
+			op_str_method {
+				v.ip++
+				sidx := int(v.read_i64())
+				argc := int(v.read_i64())
+				v.str_method(v.strings[sidx], argc)!
+			}
 			else {
 				return error('unknown opcode ${op} at ip ${v.ip}')
 			}
@@ -453,6 +640,60 @@ fn (mut v Vm) op_skeys() ! {
 	v.push(v.mkarr(v.arrays.len - 1))!
 }
 
+// op_slice slices an array or string: stack = [value, start, end] → sliced value.
+// end == -1 means "open-ended" (slice to the end).
+fn (mut v Vm) op_slice() ! {
+	v.ip++
+	end_val := v.dec_int(v.pop()!)
+	start_val := v.dec_int(v.pop()!)
+	h := v.pop()!
+	// --- array slicing ---
+	if v.is_arr(h) && v.valid_arr_handle(h) {
+		arr := v.arrays[v.hand(h)]
+		mut s := if start_val < 0 { 0 } else { int(start_val) }
+		mut e := if end_val < 0 { arr.len } else { int(end_val) }
+		if s > arr.len {
+			s = arr.len
+		}
+		if e > arr.len {
+			e = arr.len
+		}
+		if s > e {
+			e = s
+		}
+		mut sliced := []i64{}
+		for i in s..e {
+			sliced << arr[i]
+		}
+		v.arrays << sliced
+		v.push(v.mkarr(v.arrays.len - 1))!
+		return
+	}
+	// --- string slicing ---
+	if v.is_str(h) && v.valid_handle(h) {
+		src := v.strings[v.hand(h)]
+		runes := src.runes()
+		mut s := if start_val < 0 { 0 } else { int(start_val) }
+		mut e := if end_val < 0 { runes.len } else { int(end_val) }
+		if s > runes.len {
+			s = runes.len
+		}
+		if e > runes.len {
+			e = runes.len
+		}
+		if s > e {
+			e = s
+		}
+		mut sliced := ''
+		for i in s..e {
+			sliced += runes[i].str()
+		}
+		v.push(v.alloc_str(sliced))!
+		return
+	}
+	return error('slice() on a non-array, non-string value')
+}
+
 fn (mut v Vm) read_i64() i64 {
 	mut val := u64(0)
 	for i in 0..8 {
@@ -462,6 +703,15 @@ fn (mut v Vm) read_i64() i64 {
 	return i64(val)
 }
 
+fn (mut v Vm) read_f64() f64 {
+	mut val := u64(0)
+	for i in 0..8 {
+		val |= u64(v.code[v.ip + i]) << u32(8 * i)
+	}
+	v.ip += 8
+	return math.f64_from_bits(val)
+}
+
 fn (mut v Vm) push(x i64) ! {
 	if v.sp >= v.stack.len {
 		return error('stack overflow')