diff --git a/README.MD b/README.MD
index f1d740a..017b50d 100644
--- a/README.MD
+++ b/README.MD
@@ -230,7 +230,7 @@ Module functions are namespaced: `os.exists()`, `json.encode()`, ...
 | `crypto` | `sha256(s)`, `md5(s)`, `base64_encode(s)`, `base64_decode(s)` |
 | `cli` | getopt-style flag parsing over `args()`: `flag(name, default)`, `has(name)`, `positional()` — supports `--name value`, `--name=value`, boolean `--flag`, and short aliases `-n=value` |
 
-Examples: `examples/imports.vr`, `examples/http.vr`, `examples/time.vr`, `examples/cli_tool.vr` (CLI flags + interactive input + typed errors), `examples/stdlib.vr` (tests for the regex/crypto/csv/os/time additions).
+Examples: `examples/imports.vr`, `examples/http.vr`, `examples/time.vr`, `examples/cli_tool.vr` (CLI flags + interactive input + typed errors), `examples/defer_reflection.vr` (`defer`, `in`, `type_info`, `range`), `examples/stdlib.vr` (tests for the regex/crypto/csv/os/time additions).
 
 ## The VuurRaaf language
 
@@ -382,6 +382,16 @@ fn main() {
   `try { } catch e { }` like explicit `throw`s
 - 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
+- `defer <stmt>` runs the statement when the function exits (LIFO, on every
+  return path), so file/resource cleanup reads naturally: `defer remove(tmp)`
+- `x in col` membership operator works on arrays (`2 in [1,2,3]`), maps
+  (`"key" in m`), and strings (`"sub" in s`), and with `not` (`not (x in a)`)
+- `type_info(v)` reflects any value into a `{kind, is_number, is_int, is_float,
+  is_string, is_array, is_struct, is_none, is_closure, len, fields, contents}`
+  struct for duck-typing and generic utilities
+- `range(a, b)` builds `[a, a+1, ..., b)` (descends when `a > b`) as an array
+- reflection: `type(x)` returns "int"/"float"/"string"/"array"/"struct"/
+  "none"/"closure"; `keys(m)`, `has(m, k)`, `len(m)` inspect records
 - `break` / `continue` inside `while` and `for` loops (in `for` loops
   `continue` advances the loop variable / iterator first)
 - else-if chains: `if a { } else if b { } else { }`
diff --git a/bin/vc b/bin/vc
index f7a6b02..d13e171 100755
Binary files a/bin/vc and b/bin/vc differ
diff --git a/compiler/ast.v b/compiler/ast.v
index bc23670..a6880a3 100644
--- a/compiler/ast.v
+++ b/compiler/ast.v
@@ -68,6 +68,7 @@ pub enum StmtKind {
 	assert_stmt
 	try_stmt
 	throw_stmt
+	defer_stmt
 }
 
 // MatchArm is a single `value { body }` arm of a match statement.
diff --git a/compiler/check.v b/compiler/check.v
index 00f5054..de9f3be 100644
--- a/compiler/check.v
+++ b/compiler/check.v
@@ -292,6 +292,11 @@ fn (mut c Checker) check_stmt(st Stmt) ! {
 		.throw_stmt {
 			_ = c.check_expr(st.expr)!
 		}
+		.defer_stmt {
+			for s in st.body {
+				c.check_stmt(s)!
+			}
+		}
 	}
 }
 
@@ -491,7 +496,7 @@ fn (mut c Checker) check_binary(e Expr) !TypeInfo {
 			}
 			TypeInfo{ kind: .bool_t }
 		}
-		.kw_and, .kw_or {
+		.kw_and, .kw_or, .kw_in {
 			TypeInfo{ kind: .bool_t }
 		}
 		.amp, .pipe, .caret, .lt_lt, .gt_gt {
@@ -635,6 +640,8 @@ fn builtin_result_type(name string) TypeInfo {
 		'flag_val' { TypeInfo{ kind: .string_t } }
 		'flag_has' { TypeInfo{ kind: .int_t } }
 		'flag_positional' { TypeInfo{ kind: .array_t } }
+		'type_info' { TypeInfo{ kind: .struct_t } }
+		'range' { TypeInfo{ kind: .array_t } }
 		'build_is_dir' { TypeInfo{ kind: .int_t } }
 		// build-module builtins (.vrmm)
 		'build_compile', 'build_assemble', 'build_link', 'build_exec', 'build_base',
diff --git a/compiler/codegen.v b/compiler/codegen.v
index d3cae12..6817583 100644
--- a/compiler/codegen.v
+++ b/compiler/codegen.v
@@ -47,6 +47,12 @@ mut:
 	modules   map[string]bool // imported module names (bare `import os`)
 	fn_names  map[string]bool // top-level function names usable as closure values
 	captures  []string        // enclosing locals captured by the closure being compiled
+	defers    []Stmt        // deferred statements of the current function (in order)
+	has_defers bool          // current function registers deferred cleanup
+	defer_ret_slot int      // hidden local holding the return value while defers run
+	defer_value_seen bool   // a `return expr` (value) appeared, so restore+retv after defers
+	cur_defer_label string // label of the current function's deferred-cleanup block
+	namer_id  int            // unique-id source for generated label names
 }
 
 fn gen(prog Program) !obj.Obj {
@@ -226,10 +232,45 @@ fn (mut g Gen) gen_fn(fd FnDecl) ! {
 		g.code << obj.encode_i64(i64(g.argc))
 		g.code << obj.encode_i64(i64(vidx))
 	}
+	// one-pass defer handling: collect every `defer` statement in the body first
+	// (so all returns can be redirected to the deferred-cleanup block), then
+	// reserve a hidden slot to hold the return value across that block.
+	g.defers = []Stmt{}
+	g.has_defers = false
+	g.defer_value_seen = false
+	g.collect_defers(fd.body, mut g.defers)
+	if g.defers.len > 0 {
+		g.has_defers = true
+		g.defer_ret_slot = g.local_cnt
+		g.local_cnt++
+	}
+	g.cur_defer_label = g.new_label()
 	for st in fd.body {
 		g.gen_stmt(st)!
 	}
-	g.code << op_ret // trailing return for fall-through
+
+	if g.has_defers {
+		g.code << op_jmp
+		g.code << obj.encode_i64(0)
+		g.fixups << Fixup{ name: g.cur_defer_label, off: u32(g.code.len) - 8 }
+	} else {
+		g.code << op_ret // trailing return for fall-through
+	}
+	// emit the deferred-cleanup block (LIFO) then the real return here, so a
+	// `return` in the body jumps into this block and lands back on the return
+	if g.has_defers {
+		g.emit_label(g.cur_defer_label)
+		for i := g.defers.len - 1; i >= 0; i-- {
+			g.gen_stmt(g.defers[i])!
+		}
+		if g.defer_value_seen {
+			// restore the saved return value and return it
+			g.emit_load(g.defer_ret_slot)
+			g.code << op_retv
+		} else {
+			g.code << op_ret
+		}
+	}
 	// 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
@@ -245,6 +286,8 @@ fn (mut g Gen) gen_fn(fd FnDecl) ! {
 	}
 	g.fixups.clear()
 	g.labels.clear()
+	g.defers = []Stmt{} // reset for the next (possibly enclosing) function
+	g.has_defers = false
 	// snapshot the live locals as debug info for the debugger: name -> slot
 	for name, slot in g.locals {
 		g.dbg_locals << obj.DbgLocal{ fn: sym, name: name, slot: slot }
@@ -519,13 +562,34 @@ fn (mut g Gen) gen_stmt(st Stmt) ! {
 			g.emit_label(end_l)
 		}
 		.ret_stmt {
-			if st.has_val {
-				g.gen_expr(st.expr)!
-				g.code << op_retv
+			if g.has_defers {
+				// save any return value in the hidden slot, jump into the
+				// deferred-cleanup block, which restores and returns it
+				if st.has_val {
+					g.defer_value_seen = true
+					g.gen_expr(st.expr)!
+					g.emit_store(g.defer_ret_slot)
+				} else {
+					g.code << op_push_i
+					g.code << obj.encode_i64(0)
+					g.emit_store(g.defer_ret_slot)
+				}
+				g.code << op_jmp
+				g.code << obj.encode_i64(0)
+				g.fixups << Fixup{ name: g.cur_defer_label, off: u32(g.code.len) - 8 }
 			} else {
-				g.code << op_ret
+				if st.has_val {
+					g.gen_expr(st.expr)!
+					g.code << op_retv
+				} else {
+					g.code << op_ret
+				}
 			}
 		}
+		.defer_stmt {
+			// collected in gen_fn's pass and emitted in the cleanup block;
+			// nothing to place at the declaration site
+		}
 		.assert_stmt {
 			g.gen_expr(st.expr)!
 			g.code << op_assert
@@ -1047,6 +1111,9 @@ fn builtin_spec(name string) (int, int) {
 		'flag_val' { native_flag_val, 1 }
 		'flag_has' { native_flag_has, 1 }
 		'flag_positional' { native_flag_positional, 0 }
+		// structured reflection + sequence helper
+		'type_info' { native_type_info, 1 }
+		'range' { native_range, 2 }
 		'build_is_dir' { native_build_is_dir, 1 }
 		'cwd' { native_cwd, 0 }
 		'json_pretty' { native_json_pretty, 1 }
@@ -1257,6 +1324,7 @@ fn (mut g Gen) gen_binary(e Expr) ! {
 				.le { op_le }
 				.gt { op_gt }
 				.ge { op_ge }
+				.kw_in { op_in }
 				.amp { op_and_b }
 				.pipe { op_or_b }
 				.caret { op_xor }
@@ -1510,6 +1578,38 @@ fn (mut g Gen) maybe_capture(name string, bound map[string]bool, mut caps []stri
 	}
 }
 
+// collect_defers walks a statement list, gathering the inner statements of
+// every `defer` into `out` in source order. Called once per function before
+// code generation so all return sites can be redirected to the cleanup block.
+fn (mut g Gen) collect_defers(stmts []Stmt, mut out []Stmt) {
+	for st in stmts {
+		match st.kind {
+		.defer_stmt {
+			for d in st.body {
+				out << d
+			}
+		}
+			.if_stmt {
+				g.collect_defers(st.body, mut out)
+				g.collect_defers(st.els, mut out)
+			}
+			.match_stmt {
+				for a in st.arms {
+					g.collect_defers(a.body, mut out)
+				}
+				g.collect_defers(st.els_body, mut out)
+			}
+			.while_stmt, .for_range_stmt, .for_in_stmt, .try_stmt {
+				g.collect_defers(st.body, mut out)
+				if st.kind == .try_stmt {
+					g.collect_defers(st.els, mut out)
+				}
+			}
+			else {}
+		}
+	}
+}
+
 fn (mut g Gen) scan_stmt(st Stmt, mut bound map[string]bool, mut caps []string, mut seen map[string]bool) {
 	match st.kind {
 		.expr_stmt {
@@ -1623,6 +1723,11 @@ fn (mut g Gen) scan_stmt(st Stmt, mut bound map[string]bool, mut caps []string,
 		.throw_stmt {
 			g.scan_expr(st.expr, mut bound, mut caps, mut seen)
 		}
+		.defer_stmt {
+			for s in st.body {
+				g.scan_stmt(s, mut bound, mut caps, mut seen)
+			}
+		}
 		.break_stmt, .continue_stmt {}
 	}
 }
diff --git a/compiler/lexer.v b/compiler/lexer.v
index a476061..d272a47 100644
--- a/compiler/lexer.v
+++ b/compiler/lexer.v
@@ -310,6 +310,7 @@ fn (mut l Lexer) lex_ident(line int, col int) Tok {
 		'interface' { TokKind.kw_interface }
 		'try' { TokKind.kw_try }
 		'catch' { TokKind.kw_catch }
+		'defer' { TokKind.kw_defer }
 		'throw' { TokKind.kw_throw }
 		else { TokKind.ident }
 	}
diff --git a/compiler/opcodes.v b/compiler/opcodes.v
index ffb74ea..27ac7f7 100644
--- a/compiler/opcodes.v
+++ b/compiler/opcodes.v
@@ -66,6 +66,7 @@ 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), ...)
 const op_push_none = u8(62) // push the `none` sentinel
+const op_in = u8(63) // membership: x in col -> 0 or 1
 
 // native builtin ids (keep in sync with vm/opcodes.v)
 const native_abs = 100
@@ -191,3 +192,7 @@ const native_input = 196
 const native_flag_val = 197
 const native_flag_has = 198
 const native_flag_positional = 199
+
+// structured reflection + sequence helper
+const native_type_info = 200
+const native_range = 201
diff --git a/compiler/parser.v b/compiler/parser.v
index b8960e3..472c14b 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -403,6 +403,11 @@ fn (mut p Parser) parse_stmt() !Stmt {
 			body := p.parse_block()!
 			return Stmt{ kind: .for_in_stmt, target: val_name, idx_target: idx_name, expr: first, body: body, line: t.line }
 		}
+		.kw_defer {
+			p.advance()
+			inner := p.parse_stmt()!
+			return Stmt{ kind: .defer_stmt, body: [inner], line: t.line }
+		}
 		.kw_return {
 			p.advance()
 			mut e := Expr{}
@@ -664,7 +669,7 @@ fn (mut p Parser) parse_eq() !Expr {
 
 fn (mut p Parser) parse_rel() !Expr {
 	mut e := p.parse_shift()!
-	for p.cur().kind == .lt || p.cur().kind == .le || p.cur().kind == .gt || p.cur().kind == .ge {
+	for p.cur().kind == .lt || p.cur().kind == .le || p.cur().kind == .gt || p.cur().kind == .ge || p.cur().kind == .kw_in {
 		op := p.advance()
 		rhs := p.parse_shift()!
 		e = bin_node(op.kind, e, rhs, op.line)
diff --git a/compiler/tokens.v b/compiler/tokens.v
index 40938b3..4e0ddf2 100644
--- a/compiler/tokens.v
+++ b/compiler/tokens.v
@@ -69,6 +69,7 @@ pub enum TokKind {
 	kw_interface
 	kw_try
 	kw_catch
+	kw_defer
 	kw_throw
 }
 
diff --git a/examples/defer_reflection.vr b/examples/defer_reflection.vr
new file mode 100644
index 0000000..a81efcc
--- /dev/null
+++ b/examples/defer_reflection.vr
@@ -0,0 +1,53 @@
+// defer_reflection.vr — demonstrates the Batch-A features: `defer` cleanup,
+// the `in` membership operator, `type_info()` reflection, and `range()`.
+//
+//   vr run examples/defer_reflection.vr
+
+fn summarize(v) {
+    // reflection: inspect any value and build a description
+    let ti = type_info(v)
+    let kind = ti.kind
+    if ti.is_number {
+        return "a number " + str(v)
+    } else if ti.is_string {
+        return "a string of length " + str(ti.len) + ": \"" + v + "\""
+    } else if ti.is_array {
+        return "an array with " + str(ti.len) + " elements"
+    } else if ti.is_struct {
+        return "a record with fields " + str(ti.fields)
+    } else if ti.is_none {
+        return "nothing"
+    }
+    return "a " + kind
+}
+
+fn grep_lines(docs, term) {
+    // demonstrate `in` on strings + arrays, with deferred cleanup
+    let matches = []
+    defer println("  -> searched " + str(len(docs)) + " docs for \"" + term + "\"")
+    for d in docs {
+        if term in d {        // substring membership
+            push(matches, d)
+        }
+    }
+    return matches
+}
+
+fn main() {
+    // range + in + type_info
+    let nums = range(1, 6)    // [1, 2, 3, 4, 5]
+    println("nums = " + str(nums))
+    println("3 present? " + str(3 in nums))
+    println("7 present? " + str(7 in nums))
+
+    println(summarize(42))
+    println(summarize("hello"))
+    println(summarize([1, 2, 3]))
+    println(summarize({x: 1, y: 2}))
+    println(summarize(none))
+
+    println("---")
+    let docs = ["Introducing VuurRaaf", "A tiny language", "VuurRaaf: daily driver"]
+    let hits = grep_lines(docs, "VuurRaaf")
+    println("hits: " + str(hits))
+}
\ No newline at end of file
diff --git a/examples/tests.vr b/examples/tests.vr
index d18a61a..9538a9c 100644
--- a/examples/tests.vr
+++ b/examples/tests.vr
@@ -658,6 +658,83 @@ fn test_flag_parsing() {
 	assert len(flag_positional()) == 0
 }
 
+fn test_defer_cleanup() {
+	// defer runs on every exit path; its effect is visible to the caller via
+	// the shared mutable array (arrays are references).
+	let log = []
+	let a = defer_probe(log, 1)
+	assert a == 0
+	assert len(log) == 2
+	assert log[0] == "open"
+	assert log[1] == "close"
+}
+
+fn defer_probe(log, mode) {
+	push(log, "open")
+	defer push(log, "close")
+	if mode == 0 {  // early return path also runs defer
+		return 9
+	}
+	return 0
+}
+
+fn test_defer_lifo() {
+	// defers run in reverse declaration order (LIFO), all before returning
+	let logA = []
+	let r = defer_lifo(logA)
+	assert r == 0
+	assert len(logA) == 2
+	assert logA[0] == "2nd-registered"
+	assert logA[1] == "1st-registered"
+}
+
+fn defer_lifo(log) {
+	defer push(log, "1st-registered")
+	defer push(log, "2nd-registered")
+	return 0
+}
+
+fn test_in_operator() {
+	let arr = [1, 2, 3]
+	assert 2 in arr
+	assert 9 in arr == false
+	let m = {x: 1}
+	assert "x" in m
+	assert "zzz" in m == false
+	let s = "hello world"
+	assert "world" in s
+	assert "nope" in s == false
+	assert not (9 in arr)
+}
+
+fn test_range_helper() {
+	let up = range(0, 4)
+	assert len(up) == 4
+	assert up[0] == 0
+	assert up[3] == 3
+	let down = range(3, 0)
+	assert down[0] == 3
+	assert down[2] == 1
+	assert len(down) == 3
+}
+
+fn test_type_info() {
+	let ti = type_info(42)
+	assert ti.kind == "int"
+	assert ti.is_int == 1
+	assert ti.is_number == 1
+	let ts = type_info("xyz")
+	assert ts.is_string == 1
+	assert ts.len == 3
+	let tn = type_info(none)
+	assert tn.kind == "none"
+	assert tn.is_none == 1
+	let to = type_info({a: 1})
+	assert to.is_struct == 1
+	assert len(to.fields) == 1
+	assert to.fields[0] == "a"
+}
+
 fn test_failing() {
 	// this one is meant to fail — shows up in `vr test` output
 	assert 1 == 2
diff --git a/vm/native.v b/vm/native.v
index 4e2c906..dd732de 100644
--- a/vm/native.v
+++ b/vm/native.v
@@ -118,6 +118,15 @@ fn (mut v Vm) native(id int, _argc int) ! {
 			x := v.pop()!
 			v.push(v.alloc_str(v.type_name(x)))!
 		}
+		native_type_info {
+			x := v.pop()!
+			v.push(v.type_info_value(x))!
+		}
+		native_range {
+			b := v.pop()!
+			a := v.pop()!
+			v.push(v.range_value(a, b))!
+		}
 		native_split {
 			delim := v.pop_str()!
 			s := v.pop_str()!
@@ -1239,6 +1248,12 @@ fn (mut v Vm) type_name(x i64) string {
 	if v.is_float(x) {
 		return 'float'
 	}
+	if v.is_none(x) {
+		return 'none'
+	}
+	if v.is_closure(x) {
+		return 'closure'
+	}
 	if v.is_arr(x) {
 		return 'array'
 	}
@@ -1248,6 +1263,74 @@ fn (mut v Vm) type_name(x i64) string {
 	return 'int'
 }
 
+// type_info_value reflects a value into a struct for generic/duck-typed code:
+// { kind, is_number, is_int, is_float, is_string, is_array, is_struct,
+//   is_none, is_closure, len, fields } where `fields` is the array of field
+// names (structs) and `len` is the element/character count for arrays/strings.
+fn (mut v Vm) type_info_value(x i64) i64 {
+	kind := v.type_name(x)
+	is_int := v.is_int(x)
+	is_float := v.is_float(x)
+	is_string := v.is_str(x) && v.valid_handle(x)
+	is_array := v.is_arr(x) && v.valid_arr_handle(x)
+	is_struct := v.is_struct(x) && v.valid_struct_handle(x)
+	is_none := v.is_none(x)
+	is_closure := v.is_closure(x) && v.valid_closure_handle(x)
+	is_number := is_int || is_float
+	// len: array -> element count; string -> character count; struct -> field count
+	mut length := 0
+	if is_array {
+		length = v.arrays[v.hand(x)].len
+	} else if is_string {
+		length = v.strings[v.hand(x)].runes().len
+	} else if is_struct {
+		length = v.structs[v.hand(x)].fields.len
+	}
+	// fields: array of struct field names (empty otherwise)
+	mut names := []i64{}
+	if is_struct {
+		for f in v.structs[v.hand(x)].fields {
+			v.strings << f.name
+			names << v.mkstr(v.strings.len - 1)
+		}
+	}
+	v.arrays << names
+	field_h := v.mkarr(v.arrays.len - 1)
+	mut fields := []Field{}
+	fields << Field{ name: 'kind', val: v.alloc_str(kind) }
+	fields << Field{ name: 'is_number', val: v.enc_int(if is_number { 1 } else { 0 }) }
+	fields << Field{ name: 'is_int', val: v.enc_int(if is_int { 1 } else { 0 }) }
+	fields << Field{ name: 'is_float', val: v.enc_int(if is_float { 1 } else { 0 }) }
+	fields << Field{ name: 'is_string', val: v.enc_int(if is_string { 1 } else { 0 }) }
+	fields << Field{ name: 'is_array', val: v.enc_int(if is_array { 1 } else { 0 }) }
+	fields << Field{ name: 'is_struct', val: v.enc_int(if is_struct { 1 } else { 0 }) }
+	fields << Field{ name: 'is_none', val: v.enc_int(if is_none { 1 } else { 0 }) }
+	fields << Field{ name: 'is_closure', val: v.enc_int(if is_closure { 1 } else { 0 }) }
+	fields << Field{ name: 'len', val: v.enc_int(i64(length)) }
+	fields << Field{ name: 'fields', val: field_h }
+	fields << Field{ name: 'contents', val: x }
+	v.structs << StructVal{ fields: fields, by_name: v.index_fields(fields) }
+	return v.mkstruct_handle(v.structs.len - 1)
+}
+
+// range_value builds the array [a, a+1, ..., b) as ints.
+fn (mut v Vm) range_value(a i64, b i64) i64 {
+	start := v.dec_int(a)
+	end := v.dec_int(b)
+	mut arr := []i64{}
+	if start <= end {
+		for i := start; i < end; i++ {
+			arr << v.enc_int(i)
+		}
+	} else {
+		for i := start; i > end; i-- {
+			arr << v.enc_int(i)
+		}
+	}
+	v.arrays << arr
+	return v.mkarr(v.arrays.len - 1)
+}
+
 // 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.
diff --git a/vm/opcodes.v b/vm/opcodes.v
index 565ab76..48f608b 100644
--- a/vm/opcodes.v
+++ b/vm/opcodes.v
@@ -66,6 +66,7 @@ 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), ...)
 const op_push_none = u8(62) // push the `none` sentinel
+const op_in = u8(63) // membership: x in col -> 0 or 1
 
 // native builtin ids (the operand to op_native)
 const native_abs = 100
@@ -190,3 +191,7 @@ const native_input = 196
 const native_flag_val = 197
 const native_flag_has = 198
 const native_flag_positional = 199
+
+// structured reflection + sequence helper
+const native_type_info = 200
+const native_range = 201
diff --git a/vm/print.v b/vm/print.v
index 874728d..3767644 100644
--- a/vm/print.v
+++ b/vm/print.v
@@ -121,6 +121,7 @@ fn (mut v Vm) trace_op(op u8) {
 		op_varargs { 'varargs' }
 		op_str_method { 'str_method' }
 		op_push_none { 'push_none' }
+		op_in { 'in' }
 		else { '??' }
 	}
 	mut s := ''
diff --git a/vm/vm.v b/vm/vm.v
index 6517395..ea4d828 100644
--- a/vm/vm.v
+++ b/vm/vm.v
@@ -632,6 +632,27 @@ fn (mut v Vm) exec() ! {
 			op_slice {
 				v.op_slice()!
 			}
+			op_in {
+				v.ip++
+				col := v.pop()!
+				needle := v.pop()!
+				// map/struct: string key membership
+				if v.is_struct(col) && v.valid_struct_handle(col) {
+					if v.is_str(needle) && v.valid_handle(needle) {
+						key := v.strings[v.hand(needle)]
+						v.push(v.enc_int(if key in v.structs[v.hand(col)].by_name { 1 } else { 0 }))!
+					} else {
+						v.push(v.enc_int(0))!
+					}
+				} else if v.is_arr(col) && v.valid_arr_handle(col) {
+					found := v.arr_contains(v.arrays[v.hand(col)], needle)
+					v.push(v.enc_int(if found { 1 } else { 0 }))!
+				} else if v.is_str(col) && v.valid_handle(col) && v.is_str(needle) && v.valid_handle(needle) {
+					v.push(v.enc_int(if v.strings[v.hand(col)].contains(v.strings[v.hand(needle)]) { 1 } else { 0 }))!
+				} else {
+					v.push(v.enc_int(0))!
+				}
+			}
 			op_native {
 				v.ip++
 				id := int(v.read_i64())
@@ -1005,6 +1026,25 @@ fn (mut v Vm) call(target int, argc int) {
 	v.ip = target
 }
 
+// arr_contains reports whether an array holds a value equal to needle
+// (comparing ints/floats numerically and strings by content).
+fn (mut v Vm) arr_contains(a []i64, needle i64) bool {
+	for el in a {
+		if v.vals_eq(el, needle) {
+			return true
+		}
+	}
+	return false
+}
+
+// vals_eq compares two values for equality, treating int/float numerically.
+fn (mut v Vm) vals_eq(x i64, y i64) bool {
+	if (v.is_float(x) || v.is_float(y)) && !v.is_closure(x) && !v.is_closure(y) && !v.is_str(x) && !v.is_str(y) && !v.is_arr(x) && !v.is_arr(y) && !v.is_struct(x) && !v.is_struct(y) {
+		return v.to_f64(x) == v.to_f64(y)
+	}
+	return x == y
+}
+
 fn (mut v Vm) ret(with_val bool) ! {
 	retval := if with_val { v.pop()! } else { v.enc_int(0) }
 	v.sp = v.bp - 1