while loops

LANGUAGE.md

@@ -12,11 +12,12 @@
 
 ### types and expressions
 
-- exact-width `i8` through `i64`, `u8` through `u64`, `f32`, `f64`, `isize`, `usize`, `void`, and inferred integer-constrained `int`
+- exact-width `i8` through `i64`, `u8` through `u64`, `f32`, `f64`, `isize`, `usize`, `bool`, `void`, and inferred integer-constrained `int`
 - target-dependent atomic C primitives from `c_char` through `c_longdouble`
 - C primitives remain semantically distinct from exact-width Brolang primitives until target lowering
-- contextual integer literals and constant folding of addition and negation trees
+- contextual integer and character literals and constant folding of addition and negation trees
 - strict numeric conversions, checked integer addition, and unary negation
+- boolean literals, comparisons, unary `!`, and short-circuiting `and` / `or`
 - arrays `[N]T`, sentinel arrays `[N;S]T`, single-item pointers `@T`, many-item pointers `*T`, sentinel many-item pointers `[*;S]T`, pointer offsets, slices, and explicit slicing
 - immutable UTF-8 string literals typed as pointers to static sentinel arrays: `@[N;0]u8`
 - pointer-to-array `.len`, indexing, and slicing without explicit dereference
@@ -24,10 +25,12 @@
 - information-preserving and information-forgetting pointer-to-array decay and sentinel slice/pointer weakening; array values never implicitly decay
 - narrow immutable zero-terminated byte pointer conversion to `*c_char` and `[*;0]c_char`, without general `u8`/`c_char` interchange
 - optionals with trapping postfix `?`, `orelse`, and nullable pointer representation
+- conditional optional unwrapping with immutable then-block bindings: `if value |binding| { ... }`
 - source-order native structs, defined or opaque `c_struct`, and keyed record literals
 - complete plain imported C structs and unions as runtime values; incomplete or unsupported-layout records remain pointer-only
 - C function pointer types as pointer-sized runtime values, including manual `*c_func(...) T` spelling and nullable imported callback typedefs
 - postfix pointer dereference, general writable locations, function calls, assignments, and returns
+- boolean `if` statements and `while` loops with optional post-iteration assignment/expression clauses
 
 ### functions and packages
 
@@ -40,6 +43,9 @@
 - file-local relative imports, aliases, and qualified member access
 - relative `.h` imports as synthetic package namespaces
 - transitive external C function prototypes, typedef chains, C scalars, fixed arrays, complete plain records/unions, and pointers to opaque C records
+- imported external C object variables, including writable globals and immutable arrays
+- object-like scalar and plain record/union C macro constants
+- supported static inline C functions through generated external wrappers
 - bodyless manual and imported C variadic declarations with target-aware default argument promotions
 - passing concrete `c_func` declarations/definitions as C callback values and calling non-null C function pointers with postfix call syntax
 - reference-time diagnostics for unsupported imported C declarations
@@ -59,13 +65,9 @@
 ### foreign functions and linking
 
 - exporting brolang functions to c
+- additional target-specific C ABI lowering
 
 ### scalar and compound types
 
 - tuples and native variadic functions
 - C enums and non-plain C record layouts
-
-### advanced c imports
-
-- C enums, external variables, macros, and static inline functions
-- additional target-specific C ABI lowering

TODO.md

@@ -95,9 +95,12 @@
     - new `Optional_Is_Some` / `Optional_Value` IR opcodes (the `Unwrap` presence-test + extract, minus the trap)
   - conditional unwrapping with guard clause:  `if val |v : v >= 10| { ... } else { ... }` - unwrap `val` into `v` if it is not `none`
   - multi-unwrap (see section below)
-  - while loops (operates on boolean conditions). examples:
+  - while loops (implemented; operates on boolean conditions). examples:
     - `while condition { ... }` - iterate while the condition is true
-    - `while condition : i += 1 { ... }` - iterate while the condition is true and execute `i += 1` (continue expression) after each iteration
+    - `while condition : i = i + 1 { ... }` - execute the update after each completed iteration
+    - the condition and update may be parenthesized independently for visual clarity
+    - update targets must already be declared and mutable; loops do not introduce implicit induction variables
+    - compound assignment (`+=`) remains deferred
   - ranges (see section below)
   - for loops (operates on iterable sequences). examples:
     - `for items |item| { ... }` - capture just the `item` value in the array/slice (uses copy semantics, i.e. gets a `T`)
@@ -109,8 +112,11 @@
     - `for 0..(len) |i| { ... }` or equivalently `for 0..=(len - 1) |i| { ... }` - calculating range bounds, expressions must be parenthesized
   - for all conditionals/guards, parentheses are optional but allowed for visual clarity
 
-6. compound assignment
+6. compound assignment: `+=`, `-=`, `*=`, `/=`
 
+7. enums (native and c interop) (see below)
+
+8. distinct types (see below)
 
 ## A word on multi-unwrap
 
@@ -175,3 +181,59 @@ Ranges represent a sequence of values, commonly used in for loops, and is itself
 ```
   
 This rule keeps the grammar simple and forces clarity at the call site — no precedence rules to remember. Also, being a value type, ranges can be assigned to variables and passed around like any other value.
+
+# A word on distinct types
+
+Distinct types are considered distinct from their backing type. They do not implicitly coerce to their backing type.
+
+```
+# distinct type
+UserID :: distinct u32
+
+# instantiate distinct type
+my_id UserId :: UserID(42) # value must be of to backing type
+```
+
+# A word on enums
+
+```
+# standard enums
+Animal :: enum {
+    dog
+    cat
+    bird
+    lizard
+}
+
+# enums with backing type
+Nat :: enum(u8) { # in this case, a maximum of 256 values are possible
+    one # default: implicitly starts from value 0
+    two
+    three
+    four
+    five
+}
+
+# enums with backing type with explicit associated values
+# note: must not be jumbled (i.e. `first_val = 1` must come before `other_val = 2`), but is allowed to be discontiguous (i.e. `one = 1` can be followed by `three = 3` without `two = 2` in between)
+Nat :: enum(u8) {
+    one = 1
+    two = 2
+    three = 3
+    # no four
+    five = 5
+}
+
+# enums with backing type with semi-implicit associated values
+Nat :: enum(u8) {
+    one = 1 # starts from value 1
+    two     # implicitly gets value 2
+    three   # etc...
+    four
+    five
+}
+
+# using enums
+dog_tag1 Animal :: Animal.dog
+dog_tag2 Animal :: .dog # type inferred
+```

compiler/ast/ast.odin

@@ -120,6 +120,7 @@ Stmt_Kind :: enum u8 {
 	Return,
 	Expression,
 	If,
+	While,
 }
 
 Stmt :: struct {
@@ -133,8 +134,11 @@ Stmt :: struct {
 	// `If` statements use `expr` as the condition, `body` as the then-block, and
 	// `else_body` as the else-block. An `else if` chain is represented as an
 	// `else_body` holding a single nested `If` statement.
+	// `While` statements use `expr` as the condition, `body` as the loop body,
+	// and `update` as the optional post-iteration statement.
 	body:       []Stmt_Id,
 	else_body:  []Stmt_Id,
+	update:     Stmt_Id,
 	diagnostic: source.Diagnostic_Id,
 }
 

compiler/checker/checker.odin

@@ -631,6 +631,13 @@ mark_block_imports_used :: proc(checker: ^Checker, statements: []ast.Stmt_Id, fi
 			mark_expr_imports_used(checker, statement.expr, file)
 			mark_block_imports_used(checker, statement.body, file)
 			mark_block_imports_used(checker, statement.else_body, file)
+		case .While:
+			mark_expr_imports_used(checker, statement.expr, file)
+			mark_block_imports_used(checker, statement.body, file)
+			if statement.update != ast.INVALID_STMT {
+				update := [1]ast.Stmt_Id{statement.update}
+				mark_block_imports_used(checker, update[:], file)
+			}
 		case .Invalid:
 		}
 	}
@@ -1424,6 +1431,13 @@ infer_statements :: proc(
 				infer_statements(checker, statement.body, locals, pkg, file, demanded, result)
 				infer_statements(checker, statement.else_body, locals, pkg, file, demanded, result)
 			}
+		case .While:
+			_ = infer_expr(checker, statement.expr, locals^[:], pkg, file, demanded)
+			infer_statements(checker, statement.body, locals, pkg, file, demanded, result)
+			if statement.update != ast.INVALID_STMT {
+				update := [1]ast.Stmt_Id{statement.update}
+				infer_statements(checker, update[:], locals, pkg, file, demanded, result)
+			}
 		}
 	}
 	resize(locals, scope_start)
@@ -2460,7 +2474,13 @@ build_expr :: proc(
 				append(&stack, Build_Expr_Frame{expr=expr.left, expected=types.INVALID, template=ast.INVALID_FUNCTION})
 			case .Add:
 				stack[frame_index].stage = 1
-				append(&stack, Build_Expr_Frame{expr=expr.left, expected=types.INVALID, template=ast.INVALID_FUNCTION})
+				// Preserve assignment/return context for literal operands, e.g.
+				// assigning `i + 1` back into a `u32` local.
+				left_expected := types.INVALID
+				if types.is_concrete_scalar(frame.expected) && !types.is_bool(frame.expected) {
+					left_expected = frame.expected
+				}
+				append(&stack, Build_Expr_Frame{expr=expr.left, expected=left_expected, template=ast.INVALID_FUNCTION})
 			case .Call:
 				if expr.left != ast.INVALID_EXPR {
 					stack[frame_index].stage = 6
@@ -2600,6 +2620,12 @@ build_expr :: proc(
 			right_expected := types.INVALID
 			if types.is_many_pointer(checker.module.exprs[last].type, &checker.module.types) {
 				right_expected = types.USIZE
+			} else if eval_constant(checker, expr.right).kind == .Value {
+				// A constant RHS adopts the concrete LHS type before numeric
+				// compatibility is checked.
+				right_expected = checker.module.exprs[last].type
+			} else if types.is_concrete_scalar(frame.expected) && !types.is_bool(frame.expected) {
+				right_expected = frame.expected
 			}
 			append(&stack, Build_Expr_Frame{expr=expr.right, expected=right_expected, template=ast.INVALID_FUNCTION})
 			continue
@@ -3067,6 +3093,39 @@ build_block :: proc(ctx: ^Build_Ctx, statements: []ast.Stmt_Id) -> []hir.Stmt_Id
 				diagnostic = source.INVALID_DIAGNOSTIC,
 			})
 			ctx.problematic^ = ctx.problematic^ || checker.module.exprs[condition].kind == .Invalid
+		case .While:
+			condition := build_expr(
+				checker, statement.expr, ctx.locals^[:], ctx.global_reads, ctx.calls,
+				types.BOOL, ctx.pkg, ctx.file,
+			)
+			if checker.module.exprs[condition].kind != .Invalid &&
+			   !types.is_bool(checker.module.exprs[condition].type) {
+				id := source.add(checker.diagnostics, statement.span, "'while' condition must be a bool")
+				condition = invalid_hir_expr(checker, statement.span, id, types.BOOL)
+				ctx.problematic^ = true
+			}
+			loop_body := build_block(ctx, statement.body)
+			update := hir.INVALID_STMT
+			if statement.update != ast.INVALID_STMT {
+				update_ast := [1]ast.Stmt_Id{statement.update}
+				update_body := build_block(ctx, update_ast[:])
+				if len(update_body) > 0 {
+					update = update_body[0]
+				}
+				delete(update_body, checker.allocator)
+			}
+			append(&body, hir.stmt_id(len(checker.module.statements)))
+			append(&checker.module.statements, hir.Stmt{
+				kind=.While,
+				span=statement.span,
+				expr=condition,
+				then_body=loop_body,
+				update=update,
+				local=hir.INVALID_LOCAL,
+				target=hir.INVALID_EXPR,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+			ctx.problematic^ = ctx.problematic^ || checker.module.exprs[condition].kind == .Invalid
 		case .Invalid:
 			append(&body, hir.stmt_id(len(checker.module.statements)))
 			append(&checker.module.statements, hir.Stmt{
@@ -3082,8 +3141,9 @@ build_block :: proc(ctx: ^Build_Ctx, statements: []ast.Stmt_Id) -> []hir.Stmt_Id
 
 // Reports whether every control-flow path through `stmts` terminates (returns or traps),
 // so the end of the block is unreachable. A `.Return` or `.Trap` terminates outright; an
-// `.If` terminates only when it has an `else` and both arms terminate. Recursion into the
+// `.If` terminates only when it has an `else` and both arms terminate. A literal
-// `then_body`/`else_body` slices handles nested ifs and `else if` chains.
+// `while true` cannot fall through because the language has no `break` statement.
+// Recursion into the branch slices handles nested ifs and `else if` chains.
 all_paths_return :: proc(module: ^hir.Module, stmts: []hir.Stmt_Id) -> bool {
 	for id in stmts {
 		statement := module.statements[id]
@@ -3096,6 +3156,13 @@ all_paths_return :: proc(module: ^hir.Module, stmts: []hir.Stmt_Id) -> bool {
 			   all_paths_return(module, statement.else_body) {
 				return true
 			}
+		case .While:
+			if statement.expr != hir.INVALID_EXPR && int(statement.expr) < len(module.exprs) {
+				condition := module.exprs[statement.expr]
+				if condition.kind == .Bool && condition.integer != 0 {
+					return true
+				}
+			}
 		}
 	}
 	return false

compiler/hir/hir.odin

@@ -141,6 +141,7 @@ Stmt_Kind :: enum u8 {
 	Sink,
 	Trap,
 	If,
+	While,
 }
 
 Stmt :: struct {
@@ -151,8 +152,11 @@ Stmt :: struct {
 	expr:       Expr_Id,
 	// `If` statements use `expr` as the condition and `then_body`/`else_body` as
 	// the branch statement lists.
+	// `While` statements use `expr` as the condition, `then_body` as the loop
+	// body, and `update` as the optional post-iteration statement.
 	then_body:  []Stmt_Id,
 	else_body:  []Stmt_Id,
+	update:     Stmt_Id,
 	diagnostic: source.Diagnostic_Id,
 }
 

compiler/lexer/lexer.odin

@@ -26,6 +26,7 @@ keyword_kind :: proc(text: string) -> token.Kind {
 	case "and":           return .Keyword_And
 	case "or":            return .Keyword_Or
 	case "if":            return .Keyword_If
+	case "while":         return .Keyword_While
 	case "else":          return .Keyword_Else
 	case "true":          return .Keyword_True
 	case "false":         return .Keyword_False
@@ -109,8 +110,7 @@ lex :: proc(
 				cursor += 1
 				append_token(&stream, source_file, .Colon_Colon, start, cursor)
 			} else {
-				id := source.add(diagnostics, source.Span{file=source_file.id, start=source.Offset(start), end=source.Offset(cursor)}, "expected a second ':'")
+				append_token(&stream, source_file, .Colon, start, cursor)
-				append_token(&stream, source_file, .Invalid, start, cursor, diagnostic=id)
 			}
 		case '=':
 			start := cursor

compiler/llvm/llvm.odin

@@ -497,6 +497,20 @@ float_predicate :: proc(predicate: ir.Compare_Predicate) -> string {
 	return "oeq"
 }
 
+emit_entry_allocas :: proc(emitter: ^Emitter, instructions: []ir.Instruction) {
+	for instruction, instruction_index in instructions {
+		if instruction.op == .Alloca &&
+		   types.is_runtime_value(instruction.type, &emitter.module.types) {
+			fmt.sbprintf(
+				&emitter.builder,
+				"  %%v%d = alloca %s\n",
+				instruction_index,
+				llvm_type(instruction.type, &emitter.module.types),
+			)
+		}
+	}
+}
+
 emit_instruction_stream :: proc(
 	emitter: ^Emitter,
 	instructions: []ir.Instruction,
@@ -706,7 +720,9 @@ emit_instruction_stream :: proc(
 				emit_recovery_value(emitter, instruction_index, instruction, "invalid allocation type")
 				continue
 			}
-			fmt.sbprintf(&emitter.builder, "  %%v%d = alloca %s\n", instruction_index, llvm_type(instruction.type, &emitter.module.types))
+			if global_initializer {
+				fmt.sbprintf(&emitter.builder, "  %%v%d = alloca %s\n", instruction_index, llvm_type(instruction.type, &emitter.module.types))
+			}
 		case .Index_Address:
 			if !valid_instruction(instructions, instruction.a) ||
 			   !valid_value(instructions, instruction.b, types.USIZE, &emitter.module.types) {
@@ -1726,6 +1742,7 @@ emit_functions :: proc(emitter: ^Emitter) {
 			continue
 		}
 		strings.write_string(&emitter.builder, ") {\nentry:\n")
+		emit_entry_allocas(emitter, function.instructions)
 		if function.calling_convention == .C {
 			for param_type, index in function.param_types {
 				if !types.is_record(param_type, &emitter.module.types) {

compiler/lower/lower.odin

@@ -708,6 +708,60 @@ lower_statements :: proc(state: ^State, statements: []hir.Stmt_Id) {
 				target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
 				diagnostic=source.INVALID_DIAGNOSTIC,
 			})
+		case .While:
+			condition_lbl := fresh_label(state)
+			body_lbl := fresh_label(state)
+			exit_lbl := fresh_label(state)
+			update_lbl := condition_lbl
+			if statement.update != hir.INVALID_STMT {
+				update_lbl = fresh_label(state)
+			}
+			append_instruction(state, ir.Instruction{
+				op=.Br, span=statement.span, type=types.VOID, integer=condition_lbl,
+				target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+			append_instruction(state, ir.Instruction{
+				op=.Label, span=statement.span, type=types.VOID, integer=condition_lbl,
+				target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+			condition := lower_expr(state, statement.expr)
+			append_instruction(state, ir.Instruction{
+				op=.Cond_Br, span=statement.span, type=types.VOID,
+				a=condition, integer=body_lbl, target=ir.Ref(u32(exit_lbl)),
+				b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+			append_instruction(state, ir.Instruction{
+				op=.Label, span=statement.span, type=types.VOID, integer=body_lbl,
+				target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+			lower_statements(state, statement.then_body)
+			append_instruction(state, ir.Instruction{
+				op=.Br, span=statement.span, type=types.VOID, integer=update_lbl,
+				target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+			if statement.update != hir.INVALID_STMT {
+				append_instruction(state, ir.Instruction{
+					op=.Label, span=statement.span, type=types.VOID, integer=update_lbl,
+					target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+					diagnostic=source.INVALID_DIAGNOSTIC,
+				})
+				update := [1]hir.Stmt_Id{statement.update}
+				lower_statements(state, update[:])
+				append_instruction(state, ir.Instruction{
+					op=.Br, span=statement.span, type=types.VOID, integer=condition_lbl,
+					target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+					diagnostic=source.INVALID_DIAGNOSTIC,
+				})
+			}
+			append_instruction(state, ir.Instruction{
+				op=.Label, span=statement.span, type=types.VOID, integer=exit_lbl,
+				target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
 		}
 	}
 }

compiler/parser/parser.odin

@@ -928,6 +928,9 @@ parse_statement :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	if current(parser).kind == .Keyword_If {
 		return parse_if(parser)
 	}
+	if current(parser).kind == .Keyword_While {
+		return parse_while(parser)
+	}
 
 	if current(parser).kind == .Identifier || current(parser).kind == .Underscore {
 		start_cursor := parser.cursor
@@ -1123,6 +1126,96 @@ parse_if :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	return id
 }
 
+parse_while_update :: proc(parser: ^Parser) -> ast.Stmt_Id {
+	parenthesized := false
+	if _, ok := allow(parser, .Left_Paren); ok {
+		parenthesized = true
+		parser.delimiter_depth += 1
+		skip_newlines(parser)
+	}
+
+	update := ast.INVALID_STMT
+	if current(parser).kind == .Left_Brace ||
+	   current(parser).kind == .Right_Paren ||
+	   current(parser).kind == .Eof {
+		diagnostic := source.add(
+			parser.diagnostics,
+			current(parser).span,
+			"expected a while update statement after ':'",
+		)
+		update = ast.stmt_id(len(parser.module.statements))
+		append(&parser.module.statements, ast.Stmt{
+			kind=.Invalid,
+			span=current(parser).span,
+			expr=ast.INVALID_EXPR,
+			update=ast.INVALID_STMT,
+			diagnostic=diagnostic,
+		})
+	} else {
+		saved := parser.no_struct_literal
+		parser.no_struct_literal = true
+		update = parse_statement(parser)
+		parser.no_struct_literal = saved
+		statement := &parser.module.statements[update]
+		switch statement.kind {
+		case .Assignment, .Expression:
+		case .Invalid, .Declaration, .Return, .If, .While:
+			diagnostic := source.add(
+				parser.diagnostics,
+				statement.span,
+				"while update must be an assignment, sink, or expression statement",
+			)
+			statement.kind = .Invalid
+			statement.diagnostic = diagnostic
+		}
+	}
+
+	if parenthesized {
+		skip_newlines(parser)
+		if _, ok := allow(parser, .Right_Paren); !ok {
+			source.add(parser.diagnostics, current(parser).span, "expected ')' after while update")
+			for current(parser).kind != .Right_Paren &&
+			    current(parser).kind != .Left_Brace &&
+			    current(parser).kind != .Newline &&
+			    current(parser).kind != .Eof {
+				advance(parser)
+			}
+			_, _ = allow(parser, .Right_Paren)
+		}
+		parser.delimiter_depth -= 1
+	}
+	return update
+}
+
+parse_while :: proc(parser: ^Parser) -> ast.Stmt_Id {
+	start := advance(parser) // consume 'while'
+	skip_newlines(parser)
+	saved := parser.no_struct_literal
+	parser.no_struct_literal = true
+	condition := parse_expression(parser)
+	parser.no_struct_literal = saved
+	skip_newlines(parser)
+
+	update := ast.INVALID_STMT
+	if _, ok := allow(parser, .Colon); ok {
+		skip_newlines(parser)
+		update = parse_while_update(parser)
+		skip_newlines(parser)
+	}
+	body := parse_block(parser)
+
+	id := ast.stmt_id(len(parser.module.statements))
+	append(&parser.module.statements, ast.Stmt{
+		kind=.While,
+		span=span_from(start.span, previous(parser).span),
+		expr=condition,
+		body=body,
+		update=update,
+		diagnostic=source.INVALID_DIAGNOSTIC,
+	})
+	return id
+}
+
 parse_function :: proc(parser: ^Parser, name: token.Token, c_abi: bool) {
 	advance(parser)
 	if _, ok := allow(parser, .Left_Paren); !ok {

compiler/token/token.odin

@@ -13,6 +13,7 @@ Kind :: enum u8 {
 	String,
 	Character,
 	Underscore,
+	Colon,
 	Colon_Colon,
 	Equal,
 	Equal_Equal,
@@ -53,6 +54,7 @@ Kind :: enum u8 {
 	Keyword_And,
 	Keyword_Or,
 	Keyword_If,
+	Keyword_While,
 	Keyword_Else,
 	Keyword_True,
 	Keyword_False,

compiler_tests.odin

@@ -2293,6 +2293,18 @@ count_substring_occurrences :: proc(text, needle: string) -> int {
 	return count
 }
 
+find_substring_offset :: proc(text, needle: string) -> int {
+	if len(needle) == 0 {
+		return 0
+	}
+	for index := 0; index + len(needle) <= len(text); index += 1 {
+		if text[index:index + len(needle)] == needle {
+			return index
+		}
+	}
+	return -1
+}
+
 find_cimport_variable :: proc(result: ^cimport.Result, name: string) -> (^cimport.Variable, bool) {
 	for &variable in result.variables {
 		if variable.name == name {
@@ -3905,3 +3917,166 @@ if_unwrap_binding_is_immutable :: proc(t: ^testing.T) {
 	}
 	testing.expect(t, found)
 }
+
+@(test)
+while_loops_compile_and_run :: proc(t: ^testing.T) {
+	output := "/tmp/brolang-test-while-loop"
+	defer _ = os.remove(output)
+	status := compiler_core.compile_package("examples/programs/while_loop", output)
+	testing.expect_value(t, status, 0)
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 42)
+}
+
+@(test)
+while_loop_diagnostics_cover_condition_update_and_scope :: proc(t: ^testing.T) {
+	text := `bad_condition :: func() void {
+	while 1 {}
+}
+bad_unresolved :: func() void {
+	while false : missing = 1 {}
+}
+bad_immutable :: func() void {
+	i :: 0
+	while false : i = i + 1 {}
+}
+bad_body_scope :: func() void {
+	running :: false
+	while running : i = 1 {
+		i u32 = 0
+	}
+}
+bad_declaration_update :: func() void {
+	while false : i u32 = 0 {}
+}
+bad_missing_update :: func() void {
+	while false : {}
+}
+main :: func() void {
+	bad_condition()
+	bad_unresolved()
+	bad_immutable()
+	bad_body_scope()
+	bad_declaration_update()
+	bad_missing_update()
+}
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	ast_module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&ast_module)
+	hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+	defer hir.destroy_module(&hir_module)
+
+	non_bool := false
+	unresolved_missing := false
+	unresolved_body_local := false
+	immutable := false
+	disallowed := false
+	missing := false
+	for diagnostic in diagnostics.items {
+		non_bool = non_bool || strings.contains(diagnostic.message, "'while' condition must be a bool")
+		unresolved_missing = unresolved_missing || strings.contains(diagnostic.message, "cannot assign unresolved local 'missing'")
+		unresolved_body_local = unresolved_body_local || strings.contains(diagnostic.message, "cannot assign unresolved local 'i'")
+		immutable = immutable || strings.contains(diagnostic.message, "cannot assign immutable local 'i'")
+		disallowed = disallowed || strings.contains(diagnostic.message, "while update must be an assignment, sink, or expression statement")
+		missing = missing || strings.contains(diagnostic.message, "expected a while update statement after ':'")
+	}
+	testing.expect(t, non_bool)
+	testing.expect(t, unresolved_missing)
+	testing.expect(t, unresolved_body_local)
+	testing.expect(t, immutable)
+	testing.expect(t, disallowed)
+	testing.expect(t, missing)
+}
+
+@(test)
+while_true_and_potential_fallthrough_have_distinct_return_analysis :: proc(t: ^testing.T) {
+	text := `forever :: func() i32 {
+	while true {}
+}
+maybe :: func(run bool) i32 {
+	while run {
+		return 1
+	}
+}
+main :: func() void {
+	if false {
+		_ = forever()
+	}
+	_ = maybe(false)
+}
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	ast_module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&ast_module)
+	hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+	defer hir.destroy_module(&hir_module)
+
+	missing_return_count := 0
+	for diagnostic in diagnostics.items {
+		if strings.contains(diagnostic.message, "does not return a value") {
+			missing_return_count += 1
+		}
+	}
+	testing.expect_value(t, missing_return_count, 1)
+}
+
+@(test)
+while_loop_allocas_are_emitted_in_the_entry_block :: proc(t: ^testing.T) {
+	text := `main :: func() i32 {
+	i u32 = 0
+	while i < 2 and true : i = i + 1 {
+		value u32 = i
+		_ = value
+	}
+	return 0
+}
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	ast_module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&ast_module)
+	hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+	defer hir.destroy_module(&hir_module)
+	ir_module := lower.lower(&hir_module)
+	defer ir.destroy_module(&ir_module)
+	llvm_text := llvm.emit(&ir_module, &diagnostics, &symbols)
+	defer delete(llvm_text)
+
+	testing.expect_value(t, len(diagnostics.items), 0)
+	first_loop_label := find_substring_offset(llvm_text, "bro_block_")
+	testing.expect(t, first_loop_label >= 0)
+	alloca_count := 0
+	for function in ir_module.functions {
+		if !function.is_main {
+			continue
+		}
+		for instruction, instruction_index in function.instructions {
+			if instruction.op != .Alloca {
+				continue
+			}
+			alloca_count += 1
+			needle := fmt.tprintf("  %%v%d = alloca ", instruction_index)
+			offset := find_substring_offset(llvm_text, needle)
+			testing.expect(t, offset >= 0 && offset < first_loop_label)
+		}
+	}
+	testing.expect(t, alloca_count >= 3)
+}

examples/programs/while_loop/main.bro

@@ -0,0 +1,52 @@
+# Milestone 5: boolean while loops with optional post-iteration updates.
+
+return_before_update :: func() i32 {
+	i i32 = 0
+	while true : i = i + 1 {
+		return i
+	}
+}
+
+main :: func() i32 {
+	total i32 = 0
+
+	# ordinary condition and update
+	i u32 = 0
+	while i < 5 : i = i + 1 {
+		total = total + 2
+	}
+
+	# equivalent parenthesized header
+	j u32 = 0
+	while (j < 4) : (j = j + 1) {
+		total = total + 3
+	}
+
+	# nested loops and body-local storage
+	outer u32 = 0
+	while outer < 2 : outer = outer + 1 {
+		inner u32 = 0
+		while inner < 3 : inner = inner + 1 {
+			total = total + 2
+		}
+	}
+
+	# The body-local k shadows only inside the body. The update still targets
+	# the mutable k declared before the loop.
+	k u32 = 0
+	while k < 4 : k = k + 1 {
+		k u32 = 100
+		if k == 100 {
+			total = total + 2
+		}
+	}
+
+	# zero iterations
+	while false {
+		total = total + 100
+	}
+
+	# A return exits before the update clause.
+	total = total + return_before_update()
+	return total
+}