diff --git a/compiler/ast.v b/compiler/ast.v
index 4b42c70..f04fc58 100644
--- a/compiler/ast.v
+++ b/compiler/ast.v
@@ -122,7 +122,8 @@ pub mut:
 
 pub struct ImportDecl {
 pub mut:
-	path string
+	path string // the file to load (module name for bare `import os`)
+	name string // module name ('' for quoted file imports: flat merge)
 	line int
 }
 
diff --git a/compiler/check.v b/compiler/check.v
index 8332167..fd2a101 100644
--- a/compiler/check.v
+++ b/compiler/check.v
@@ -46,7 +46,8 @@ mut:
 	enums   map[string][]string
 	consts  map[string]TypeInfo
 	loop_depth int
-	checked map[string]bool // imported files already checked
+	checked map[string]bool  // imported files already checked
+	modules map[string]bool  // imported module names (bare `import os`)
 }
 
 // check validates a parsed program and returns an error on the first problem.
@@ -76,7 +77,10 @@ fn check(prog Program) ! {
 	}
 	// imported files are checked (and their symbols merged) recursively
 	for imp in prog.imports {
-		c.check_import(imp.path)!
+		if imp.name.len > 0 {
+			c.modules[imp.name] = true
+		}
+		c.check_import(imp.path, imp.name)!
 	}
 	for fd in prog.fns {
 		c.check_fn(fd)!
@@ -93,7 +97,7 @@ fn def_count(fd FnDecl) int {
 	return n
 }
 
-fn (mut c Checker) check_import(path string) ! {
+fn (mut c Checker) check_import(path string, mod_name string) ! {
 	if path in c.checked {
 		return
 	}
@@ -101,7 +105,9 @@ fn (mut c Checker) check_import(path string) ! {
 	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
+	// merge declarations from the import (bare modules register their
+	// functions under both the bare name and the "mod.fn" name, so internal
+	// calls check against the former and program calls against the latter)
 	for sd in prog.structs {
 		if sd.name !in c.structs {
 			c.structs[sd.name] = sd.fields
@@ -121,9 +127,15 @@ fn (mut c Checker) check_import(path string) ! {
 		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 }
 		}
+		if mod_name.len > 0 {
+			key := '${mod_name}.${fd.name}'
+			if key !in c.fns {
+				c.fns[key] = 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)!
+		c.check_import(imp.path, imp.name)!
 	}
 	for fd in prog.fns {
 		c.check_fn(fd)!
@@ -324,16 +336,35 @@ fn (mut c Checker) check_expr(e Expr) !TypeInfo {
 			}
 			TypeInfo{ kind: .unknown }
 		}
-		.method_call {
-			recv := c.check_expr(*e.left)!
-			if recv.kind == .int_t || recv.kind == .float_t || recv.kind == .bool_t || recv.kind == .none_t {
-				return error('cannot call a method on a ${type_name(recv.kind)} (line ${e.line})')
-			}
+	.method_call {
+		// module call: os.exists(x) — the receiver is an imported module name
+		if e.left.kind == .ident && e.left.name in c.modules {
 			for a in e.args {
 				_ = c.check_expr(a)!
 			}
-			TypeInfo{ kind: .unknown }
+			key := '${e.left.name}.${e.name}'
+			if key in c.fns {
+				sig := c.fns[key]
+				if !sig.variadic {
+					if e.args.len < sig.min_args {
+						return error('${key}() expects at least ${sig.min_args} argument(s), got ${e.args.len} (line ${e.line})')
+					}
+					if e.args.len > sig.has_defs.len {
+						return error('${key}() expects at most ${sig.has_defs.len} argument(s), got ${e.args.len} (line ${e.line})')
+					}
+				}
+			}
+			return TypeInfo{ kind: .unknown }
 		}
+		recv := c.check_expr(*e.left)!
+		if recv.kind == .int_t || recv.kind == .float_t || recv.kind == .bool_t || recv.kind == .none_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)!
@@ -560,6 +591,8 @@ fn builtin_result_type(name string) TypeInfo {
 		// stdlib: JSON + string formatting
 		'json_encode', 'format', 'replace', 'pad', 'pad_left', 'repeat' { TypeInfo{ kind: .string_t } }
 		'json_decode', 'split_lines' { TypeInfo{ kind: .unknown } }
+		'cwd', 'json_pretty' { TypeInfo{ kind: .string_t } }
+		'build_is_dir' { TypeInfo{ kind: .int_t } }
 		// build-module builtins (.vrmm)
 		'build_compile', 'build_assemble', 'build_link', 'build_exec', 'build_base',
 		'build_dir', 'build_join', 'build_root' { TypeInfo{ kind: .string_t } }
diff --git a/compiler/codegen.v b/compiler/codegen.v
index 4d56de7..3d7d789 100644
--- a/compiler/codegen.v
+++ b/compiler/codegen.v
@@ -43,6 +43,7 @@ mut:
 	loops     []LoopCtx
 	enter_off u32
 	next_lbl  int
+	modules   map[string]bool // imported module names (bare `import os`)
 }
 
 fn gen(prog Program) !obj.Obj {
@@ -78,22 +79,41 @@ fn gen(prog Program) !obj.Obj {
 		}
 		g.structs[sd.name] = sd.fields
 	}
-	// compile imported files and merge their objects
+	// compile imported files and merge their objects. Bare module imports
+	// (`import os`) prefix the module's function symbols and internal call
+	// relocations with "os.", so programs call os.exists(...) and modules can
+	// never collide with each other or with the program's own functions.
 	for imp in prog.imports {
+		mod_name := imp.name
+		prefix := if mod_name.len > 0 { mod_name + '.' } else { '' }
 		imported := compile_file(resolve_import(imp.path)!)!
-		// merge symbols from the imported object
+		if mod_name.len > 0 {
+			g.modules[mod_name] = true
+		}
+		// the imported object's own symbol names (for rewriting call sites)
+		mut own := map[string]bool{}
 		for s in imported.symbols {
-			g.symbols << s
+			own[s.name] = true
+		}
+		// append imported bytecode first so symbol entries can be rebased
+		code_off := g.code.len
+		g.code << imported.code
+		// merge symbols from the imported object (prefixed and rebased: entries
+		// are relative to the imported code, which now sits at code_off)
+		for s in imported.symbols {
+			g.symbols << obj.Symbol{ name: prefix + s.name, entry: code_off + s.entry }
 		}
 		// merge strings
 		for s in imported.strings {
 			g.strings << s
 		}
-		// append imported bytecode and adjust relocations
-		code_off := g.code.len
-		g.code << imported.code
+		// adjust relocations (and prefix module-internal call targets)
 		for r in imported.relocs {
-			g.relocs << obj.Reloc{ offset: u32(code_off) + r.offset, name: r.name, kind: r.kind }
+			mut rname := r.name
+			if r.kind == 0 && prefix.len > 0 && r.name in own {
+				rname = prefix + r.name
+			}
+			g.relocs << obj.Reloc{ offset: u32(code_off) + r.offset, name: rname, kind: r.kind }
 		}
 		// merge debug info, rebasing offsets into this object's code space
 		for l in imported.lines {
@@ -190,12 +210,14 @@ fn (mut g Gen) gen_fn(fd FnDecl) ! {
 	// 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
+	// resolve intra-function jump targets. Targets are encoded PC-relative
+	// (delta from the end of the 8-byte operand), so bytecode stays
+	// position-independent when module objects are merged or linked.
 	for f in g.fixups {
 		target := g.labels[f.name] or {
 			return error('internal error: unresolved label ${f.name} in fn ${fd.name}')
 		}
-		obj.patch_i64(mut g.code, f.off, i64(target))
+		obj.patch_i64(mut g.code, f.off, i64(target - (int(f.off) + 8)))
 	}
 	g.fixups.clear()
 	g.labels.clear()
@@ -603,13 +625,24 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 			g.emit_field_name(e.name)
 			g.code << op_sget
 		}
-		.method_call {
-			// p.dist(x)  →  call <Type>.dist  p, x
-			recv_t := g.method_receiver_type(e)
-			// string methods: s.len(), s.to_upper(), s.contains(x), ... —
-			// the receiver type is known when it is a literal or a local that
-			// was assigned a string literal
-			if recv_t == 'string' || e.left.kind == .str_lit {
+	.method_call {
+		// module call: os.exists(x) — the receiver is an imported module name
+		if e.left.kind == .ident && e.left.name in g.modules {
+			for a in e.args {
+				g.gen_expr(a)!
+			}
+			g.code << op_call
+			g.code << obj.encode_i64(0) // placeholder — patched by the linker
+			g.relocs << obj.Reloc{ offset: u32(g.code.len) - 8, name: '${e.left.name}.${e.name}', kind: 0 }
+			g.code << obj.encode_i64(i64(e.args.len))
+			return
+		}
+		// p.dist(x)  →  call <Type>.dist  p, x
+		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)!
@@ -713,8 +746,9 @@ fn (mut g Gen) gen_expr(e Expr) ! {
 			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))
+			// Patch the skip jump to land at the closure opcode we emit next
+			// (PC-relative, like all other jump targets).
+			obj.patch_i64(mut g.code, skip_fix_off, i64(g.code.len - (int(skip_fix_off) + 8)))
 			g.code << op_closure
 			g.code << obj.encode_i64(0)
 			g.relocs << obj.Reloc{ offset: u32(g.code.len) - 8, name: name, kind: 0 }
@@ -830,10 +864,12 @@ 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
+	// closure call: ident(args) where ident is a local holding a closure.
+	// The local's value is pushed as the call sequence's first slot;
+	// op_call_closure consumes it along with the args, leaving only the
+	// result on the stack.
 	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)!
 		}
@@ -935,6 +971,9 @@ fn builtin_spec(name string) (int, int) {
 		'pad' { native_pad, 2 }
 		'pad_left' { native_pad_left, 2 }
 		'repeat' { native_repeat, 2 }
+		'build_is_dir' { native_build_is_dir, 1 }
+		'cwd' { native_cwd, 0 }
+		'json_pretty' { native_json_pretty, 1 }
 		else { -1, 0 }
 	}
 }
@@ -1166,6 +1205,7 @@ fn (mut g Gen) expr_type(e Expr) string {
 			'build_compile', 'build_assemble', 'build_link', 'build_exec', 'build_base',
 			'build_dir', 'build_join', 'build_root' { 'string' }
 			'json_encode', 'format', 'replace', 'pad', 'pad_left', 'repeat' { 'string' }
+			'cwd', 'json_pretty' { 'string' }
 			else { '' }
 		}
 	}
diff --git a/compiler/compiler.v b/compiler/compiler.v
index e1db6f0..da3f70d 100644
--- a/compiler/compiler.v
+++ b/compiler/compiler.v
@@ -4,6 +4,10 @@ module compiler
 import os
 import obj
 
+// stdlib_dir is the toolchain's bundled library (lib/*.vr), resolved at build
+// time so `import os` works from any working directory.
+const stdlib_dir = @VMODROOT + '/lib'
+
 // compile parses and compiles VuurRaaf source into an object file.
 pub fn compile(src string) !obj.Obj {
 	toks := tokenize(src)!
@@ -19,16 +23,19 @@ pub fn compile_file(path string) !obj.Obj {
 }
 
 // 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.
+// the path as given first, then the package-manager layout (vendor/) and the
+// toolchain's own standard library (lib/), so both `import "pkg/file.vr"`
+// and the bare module form `import os` resolve from anywhere.
 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'] {
+	for cand in ['vendor/${path}', 'vendor/${path}.vr', 'vendor/${path}/main.vr',
+		'vendor/${path}/src/main.vr', os.join_path(stdlib_dir, path + '.vr'),
+		os.join_path(stdlib_dir, path, 'main.vr')] {
 		if os.exists(cand) {
 			return cand
 		}
 	}
-	return error('cannot resolve import "${path}" (tried vendor/)"')
+	return error('cannot resolve import "${path}" (tried vendor/ and lib/)')
 }
diff --git a/compiler/opcodes.v b/compiler/opcodes.v
index c80133a..7b2373f 100644
--- a/compiler/opcodes.v
+++ b/compiler/opcodes.v
@@ -138,3 +138,6 @@ const native_split_lines = 161
 const native_pad = 162
 const native_pad_left = 163
 const native_repeat = 164
+const native_build_is_dir = 165
+const native_cwd = 166
+const native_json_pretty = 167
diff --git a/compiler/parser.v b/compiler/parser.v
index e01a076..699dab5 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -2,7 +2,7 @@
 //
 // Grammar (informal):
 //   program  := import* (struct | enum | const | fn)*
-//   import   := 'import' STRING
+//   import   := 'import' STRING | 'import' IDENT
 //   struct   := 'struct' IDENT '{' [IDENT (',' IDENT)*] '}'
 //   enum     := 'enum' IDENT '{' [IDENT (',' IDENT)*] '}'
 //   const    := 'const' IDENT '=' expr
@@ -123,11 +123,16 @@ fn (mut p Parser) parse_struct_decl() !StructDecl {
 	return StructDecl{ name: name.lit, fields: fields, line: t.line }
 }
 
-// parse_import parses `import "path/to/file.vr"`.
+// parse_import parses `import "path/to/file.vr"` (flat file merge) or a
+// bare module name like `import os` (namespaced stdlib/vendor module).
 fn (mut p Parser) parse_import() !ImportDecl {
 	t := p.expect(.kw_import, "'import'")!
-	path := p.expect(.str_lit, 'import path')!
-	return ImportDecl{ path: path.lit, line: t.line }
+	if p.cur().kind == .str_lit {
+		path := p.advance().lit
+		return ImportDecl{ path: path, line: t.line }
+	}
+	name := p.expect(.ident, 'module name')!.lit
+	return ImportDecl{ name: name, path: name, line: t.line }
 }
 
 // parse_enum_decl parses `enum Name { variant1 variant2 ... }`.
diff --git a/examples/imports.vr b/examples/imports.vr
new file mode 100644
index 0000000..69e2821
--- /dev/null
+++ b/examples/imports.vr
@@ -0,0 +1,44 @@
+// imports.vr — the bundled standard library, imported by name like in V.
+//   vr run examples/imports.vr
+//
+// The toolchain ships lib/*.vr; `import os` resolves against it (and vendor/)
+// from any working directory. Module functions are namespaced: os.exists(),
+// json.encode(), strings.join(), math.clamp().
+
+import os
+import json
+import strings
+import math
+
+fn main() {
+	// --- os: filesystem helpers ---
+	println("cwd: " + os.cwd())
+	println("lib has json.vr: " + str(os.exists("lib/json.vr")))
+	for f in os.list_dir("lib") {
+		println("  lib/" + f)
+	}
+
+	// --- json: encode / decode / pretty ---
+	let user = {
+		name: "amy",
+		age: 30,
+		score: 87.5,
+		tags: ["admin", "beta"],
+		active: 1
+	}
+	println(json.pretty(user))
+
+	let back = json.decode(json.encode(user))
+	println("decoded back: " + back.name + ", " + str(back.age))
+
+	// --- strings: namespaced string API ---
+	println(strings.join(["one", "two", "three"], ", "))
+	println(strings.capitalize("vuurraaf"))
+	println(strings.pad_left("42", 5) + "|")
+	println(strings.repeat("ab", 3))
+
+	// --- math ---
+	println(str(math.clamp(150, 0, 100)))
+	println(str(math.sign(-42)))
+	println(strings.format(math.pi(), "%.4f"))
+}
diff --git a/examples/tests.vr b/examples/tests.vr
index 12119da..2c05d09 100644
--- a/examples/tests.vr
+++ b/examples/tests.vr
@@ -1,6 +1,11 @@
 // tests.vr — functions named test_* are picked up by `vr test`.
 //   vr test examples/tests.vr
 
+import os
+import json
+import strings
+import math
+
 fn add(a, b) {
 	return a + b
 }
@@ -292,6 +297,43 @@ fn test_none() {
 	assert not (none == 1)
 }
 
+fn test_module_imports() {
+	// os module
+	if not os.exists("examples") {
+		assert false
+	}
+	if not os.is_dir("examples") {
+		assert false
+	}
+	if not os.is_file("main.v") {
+		assert false
+	}
+	assert os.base("a/b/c.vr") == "c.vr"
+	assert os.dir("a/b/c.vr") == "a/b"
+	assert len(os.glob("lib/*.vr")) == 4
+	let tmp = os.join(os.cwd(), "tmp_test.txt")
+	os.write_lines(tmp, ["x", "y"])
+	assert len(os.read_lines(tmp)) == 2
+	os.remove(tmp)
+
+	// json module
+	let data = json.decode("{\"a\": 1, \"b\": [2, 3]}")
+	assert json.encode(data) == "{\"a\":1,\"b\":[2,3]}"
+	assert strings.contains(json.pretty(data), "\n")
+
+	// strings module
+	assert strings.join(["a", "b"], "-") == "a-b"
+	assert strings.capitalize("hello") == "Hello"
+	assert strings.replace("foo", "o", "0") == "f00"
+	assert strings.pad_left("7", 3) == "  7"
+	assert strings.format(3.14159, "%.2f") == "3.14"
+
+	// math module
+	assert math.clamp(150, 0, 100) == 100
+	assert math.sign(-3) == -1
+	assert math.abs(-7) == 7
+}
+
 fn test_native_errors_are_catchable() {
 	try {
 		read_file("/no/such/file.vr")
@@ -307,6 +349,38 @@ fn test_native_errors_are_catchable() {
 	}
 }
 
+fn test_closures() {
+	// closures in expression contexts must not corrupt surrounding values
+	let pick = fn (x) {
+		if x > 10 {
+			return "big"
+		}
+		return "small"
+	}
+	assert "a: " + pick(50) == "a: big"
+	assert pick(3) + "!" == "small!"
+	assert pick(50) + " " + pick(3) == "big small"
+	let dbl = fn (x) {
+		return x * 2
+	}
+	assert str(dbl(21)) == "42"
+	assert "v=" + str(dbl(4)) == "v=8"
+	// closure containing a loop
+	let sum = fn () {
+		let total = 0
+		for i in 0..5 {
+			total = total + i
+		}
+		return total
+	}
+	assert sum() == 10
+	// closure call as a statement argument
+	let tag = fn (t) {
+		return "[" + t + "]"
+	}
+	assert tag("warn") == "[warn]"
+}
+
 fn test_failing() {
 	// this one is meant to fail — shows up in `vr test` output
 	assert 1 == 2
diff --git a/lib/json.vr b/lib/json.vr
new file mode 100644
index 0000000..fa17305
--- /dev/null
+++ b/lib/json.vr
@@ -0,0 +1,18 @@
+// json.vr — JSON helpers (part of the VuurRaaf stdlib).
+//
+//   import json
+//   let data = json.decode("{\"a\": 1}")
+//   println(json.encode(data))
+//   println(json.pretty(data))
+
+fn encode(x) {
+	return json_encode(x)
+}
+
+fn decode(s) {
+	return json_decode(s)
+}
+
+fn pretty(x) {
+	return json_pretty(x)
+}
diff --git a/lib/math.vr b/lib/math.vr
new file mode 100644
index 0000000..a51ddfa
--- /dev/null
+++ b/lib/math.vr
@@ -0,0 +1,61 @@
+// math.vr — math helpers (part of the VuurRaaf stdlib).
+//
+//   import math
+//   println(math.clamp(150, 0, 100))
+//   println(math.sign(-3))
+
+fn abs(x) {
+	return abs(x)
+}
+
+fn min(a, b) {
+	return min(a, b)
+}
+
+fn max(a, b) {
+	return max(a, b)
+}
+
+fn floor(x) {
+	return floor(x)
+}
+
+fn ceil(x) {
+	return ceil(x)
+}
+
+fn round(x) {
+	return round(x)
+}
+
+fn sqrt(x) {
+	return sqrt(x)
+}
+
+fn pow(a, b) {
+	return pow(a, b)
+}
+
+fn clamp(x, lo, hi) {
+	if x < lo {
+		return lo
+	}
+	if x > hi {
+		return hi
+	}
+	return x
+}
+
+fn sign(x) {
+	if x < 0 {
+		return -1
+	}
+	if x > 0 {
+		return 1
+	}
+	return 0
+}
+
+fn pi() {
+	return 3.14159
+}
diff --git a/lib/os.vr b/lib/os.vr
new file mode 100644
index 0000000..5830bc2
--- /dev/null
+++ b/lib/os.vr
@@ -0,0 +1,75 @@
+// os.vr — operating system and filesystem helpers (part of the VuurRaaf stdlib).
+//
+//   import os
+//   if os.exists("build.vrmm") {
+//       for f in os.list_dir(".") {
+//           println(f)
+//       }
+//   }
+
+fn exists(path) {
+	return build_exists(path)
+}
+
+fn is_dir(path) {
+	return build_is_dir(path)
+}
+
+fn is_file(path) {
+	return build_exists(path) and not build_is_dir(path)
+}
+
+fn mkdir(path) {
+	build_mkdir(path)
+	return 0
+}
+
+fn remove(path) {
+	return build_rm(path)
+}
+
+fn copy(src, dst) {
+	build_copy(src, dst)
+	return 0
+}
+
+fn list_dir(path) {
+	return build_ls(path)
+}
+
+fn glob(pattern) {
+	return build_glob(pattern)
+}
+
+fn join(a, b) {
+	return build_join(a, b)
+}
+
+fn base(path) {
+	return build_base(path)
+}
+
+fn dir(path) {
+	return build_dir(path)
+}
+
+fn read_lines(path) {
+	return split_lines(read_file(path))
+}
+
+fn write_lines(path, lines) {
+	write_file(path, join(lines, "\n") + "\n")
+	return 0
+}
+
+fn cwd() {
+	return cwd()
+}
+
+fn env(name) {
+	return getenv(name)
+}
+
+fn exec(cmd) {
+	return build_exec(cmd)
+}
diff --git a/lib/strings.vr b/lib/strings.vr
new file mode 100644
index 0000000..38e8d9e
--- /dev/null
+++ b/lib/strings.vr
@@ -0,0 +1,72 @@
+// strings.vr — string helpers (part of the VuurRaaf stdlib).
+//
+//   import strings
+//   println(strings.join(["a", "b"], ", "))
+//   println(strings.capitalize("hello"))
+
+fn length(s) {
+	return len(s)
+}
+
+fn lines(s) {
+	return split_lines(s)
+}
+
+fn split(s, delim) {
+	return split(s, delim)
+}
+
+fn join(parts, delim) {
+	return join(parts, delim)
+}
+
+fn replace(s, from, to) {
+	return replace(s, from, to)
+}
+
+fn contains(s, sub) {
+	return contains(s, sub)
+}
+
+fn starts_with(s, prefix) {
+	return starts_with(s, prefix)
+}
+
+fn ends_with(s, suffix) {
+	return ends_with(s, suffix)
+}
+
+fn upper(s) {
+	return upper(s)
+}
+
+fn lower(s) {
+	return lower(s)
+}
+
+fn trim(s) {
+	return trim(s)
+}
+
+fn pad(s, width) {
+	return pad(s, width)
+}
+
+fn pad_left(s, width) {
+	return pad_left(s, width)
+}
+
+fn repeat(s, n) {
+	return repeat(s, n)
+}
+
+fn format(x, spec) {
+	return format(x, spec)
+}
+
+fn capitalize(s) {
+	if len(s) == 0 {
+		return s
+	}
+	return upper(s[0]) + s[1..]
+}
diff --git a/vm/json.v b/vm/json.v
index 825c120..b04dfe1 100644
--- a/vm/json.v
+++ b/vm/json.v
@@ -421,6 +421,52 @@ fn (mut v Vm) json_encode_value(x i64, depth int) !string {
 	return v.dec_int(x).str()
 }
 
+// json_pretty_value renders a value as indented, multi-line JSON (the
+// `json_pretty` builtin used by the json stdlib module).
+fn (mut v Vm) json_pretty_value(x i64, depth int) !string {
+	ind := '  '.repeat(depth)
+	ind1 := '  '.repeat(depth + 1)
+	if v.is_none(x) {
+		return 'null'
+	}
+	if v.is_str(x) && v.valid_handle(x) {
+		return json_quote(v.strings[v.hand(x)])
+	}
+	if v.is_arr(x) && v.valid_arr_handle(x) {
+		a := v.arrays[v.hand(x)]
+		if a.len == 0 {
+			return '[]'
+		}
+		mut parts := []string{}
+		for el in a {
+			parts << ind1 + v.json_pretty_value(el, depth + 1)!
+		}
+		return '[\n' + parts.join(',\n') + '\n' + ind + ']'
+	}
+	if v.is_struct(x) && v.valid_struct_handle(x) {
+		s := v.structs[v.hand(x)]
+		if s.fields.len == 0 {
+			return '{}'
+		}
+		mut parts := []string{}
+		for f in s.fields {
+			parts << ind1 + json_quote(f.name) + ': ' + v.json_pretty_value(f.val, depth + 1)!
+		}
+		return '{\n' + parts.join(',\n') + '\n' + ind + '}'
+	}
+	if v.is_float(x) && v.valid_float_handle(x) {
+		f := v.fval(x)
+		if math.is_nan(f) || math.is_inf(f, 1) || math.is_inf(f, -1) {
+			return error('cannot encode NaN or Infinity as JSON')
+		}
+		return fmt_float(f)
+	}
+	if v.is_closure(x) && v.valid_closure_handle(x) {
+		return error('cannot encode a function value as JSON')
+	}
+	return v.dec_int(x).str()
+}
+
 // json_quote escapes a string into a JSON string literal. UTF-8 bytes pass
 // through untouched; control characters become \\u00XX escapes.
 fn json_quote(s string) string {
diff --git a/vm/native.v b/vm/native.v
index 3f82b3e..0d2e338 100644
--- a/vm/native.v
+++ b/vm/native.v
@@ -513,6 +513,10 @@ fn (mut v Vm) native(id int, _argc int) ! {
 			p := v.pop_str()!
 			v.push(v.enc_int(bool_i64(os.exists(p))))!
 		}
+		native_build_is_dir {
+			p := v.pop_str()!
+			v.push(v.enc_int(bool_i64(os.is_dir(p))))!
+		}
 		native_build_mkdir {
 			p := v.pop_str()!
 			os.mkdir_all(p) or { return error('build_mkdir: cannot create ${p}: ${err.msg()}') }
@@ -635,6 +639,14 @@ fn (mut v Vm) native(id int, _argc int) ! {
 			}
 			v.push(v.alloc_str(s.repeat(n)))!
 		}
+		native_cwd {
+			v.push(v.alloc_str(os.getwd()))!
+		}
+		native_json_pretty {
+			x := v.pop()!
+			s := v.json_pretty_value(x, 0) or { return error('json_pretty: ${err.msg()}') }
+			v.push(v.alloc_str(s))!
+		}
 		else {
 			return error('unknown native builtin ${id}')
 		}
diff --git a/vm/opcodes.v b/vm/opcodes.v
index 823f7d8..d24a644 100644
--- a/vm/opcodes.v
+++ b/vm/opcodes.v
@@ -137,3 +137,6 @@ const native_split_lines = 161
 const native_pad = 162
 const native_pad_left = 163
 const native_repeat = 164
+const native_build_is_dir = 165
+const native_cwd = 166
+const native_json_pretty = 167
diff --git a/vm/vm.v b/vm/vm.v
index c1526db..56bec0b 100644
--- a/vm/vm.v
+++ b/vm/vm.v
@@ -239,20 +239,22 @@ fn (mut v Vm) exec() ! {
 			}
 			op_jmp {
 				v.ip++
-				v.ip = int(v.read_i64())
+				// jump targets are PC-relative (delta from the end of the
+				// operand), so merged/linked bytecode stays position-independent
+				v.ip += int(v.read_i64())
 			}
 			op_jz {
 				v.ip++
 				target := int(v.read_i64())
 				if !v.truthy(v.pop()!) {
-					v.ip = target
+					v.ip += target
 				}
 			}
 			op_jnz {
 				v.ip++
 				target := int(v.read_i64())
 				if v.truthy(v.pop()!) {
-					v.ip = target
+					v.ip += target
 				}
 			}
 			op_call {
@@ -499,7 +501,7 @@ fn (mut v Vm) exec() ! {
 			}
 			op_try {
 				v.ip++
-				catch_ip := int(v.read_i64())
+				catch_ip := int(v.read_i64()) + v.ip
 				v.handlers << Handler{ ip: catch_ip, bp: v.bp, sp: v.sp }
 			}
 			op_throw {
@@ -536,15 +538,15 @@ fn (mut v Vm) exec() ! {
 					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.
+				// Shift args left to overwrite the closure slot (and drop the
+				// duplicated tail), so the callee's retv lands exactly where the
+				// call sequence began and no stale value is left below the
+				// result. The caller's own local holding the closure sits below
+				// the pushed sequence and is never touched.
 				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.sp-- // drop the duplicated arg tail; closure slot was consumed
 				v.call(entry, argc)
 			}
 			op_argc {