comptime eval

LANGUAGE.md

@@ -54,6 +54,7 @@ roadmap and milestone history.
 - demand-monomorphized Brolang and C-ABI functions
 - integer comptime value parameters such as `make_array func($N usize) [N]u8`, specialized by value and omitted from the runtime ABI
 - explicit comptime type parameters such as `max func($T type, a, b T) T`, specialized by type and omitted from the runtime ABI
+- forced comptime expressions such as `$sum(1, 2)` and comptime value blocks such as `${ yield 4 }` for integer constant contexts
 - bodyful `c_func` definitions and bodyless `c_func` declarations with exact external symbol names
 - concrete-only C signatures, C variadic declarations/calls, and C default argument promotions
 - Apple Silicon C ABI lowering for scalars, pointers, fixed-signature plain records/unions, small aggregates, homogeneous float aggregates, and indirect aggregate returns
@@ -81,7 +82,7 @@ roadmap and milestone history.
 
 ## PLANNED / DEFERRED
 
-- comptime-evaluable functions
+- broader Zig-style comptime execution
 - tuples and native Brolang variadic functions
 - exporting Brolang functions to C and broader target-specific C ABI lowering
 - non-plain C record layouts such as bitfields, packed records, flexible arrays, qualified fields, and C variadic record arguments

README.md

@@ -137,6 +137,7 @@ Current prototype features:
 - Qualified imported globals and functions with package-aware symbol mangling
 - Demand-monomorphized Brolang and C-ABI functions
 - Integer and type comptime parameters (`func($N usize) [N]u8`, `func($T type, value T) T`) specialized by comptime argument
+- Forced comptime expressions (`$sum(1, 2)`) and comptime value blocks (`${ yield 4 }`) for integer constant contexts
 - Bodyless concrete C function declarations with exact external symbol names
 - Bodyless manual and imported C variadic declarations with default argument promotions
 - Ordered linking of additional C sources, objects, archives, and libraries

TODO.md

@@ -651,7 +651,29 @@
     inferred type parameters, first-class type values, or comptime execution
 
 27.6 comptime-evaluable constants/functions
-  - planned shape: `$x :: 32` and `$sum func(a, b int) int { ... }`
+  - `$expr` forces comptime evaluation of an expression:
+    `x :: $32`, `n :: $sum(1, 2)`, and `res :: ${ ... }`
+  - constant contexts such as array counts and comptime value arguments implicitly
+    require comptime evaluation; ordinary immutable bindings remain ordinary bindings
+  - ordinary `func` calls are comptime-evaluable when reached from a comptime context;
+    do not add a separate `$sum func(...)` declaration form
+  - v1 evaluator supports integer literals/arithmetic, boolean conditions, immutable
+    locals, `return`, `if`/`else`, comptime blocks, and direct calls to other evaluable
+    brolang functions
+  - broader Zig-style comptime execution is milestone 27.7
+
+27.7 broader Zig-style comptime execution
+  - extend the comptime evaluator from integer scalars into a real compile-time value
+    model: bools, floats, strings, arrays/slices, structs/unions/enums, optionals,
+    fallibles, and pointers to comptime storage
+  - support mutable comptime locals/assignment, loops with an evaluation quota,
+    `defer`, `match`, value blocks/`yield`, and `try`/`catch`
+  - allow calls through comptime-known function values/function pointers; keep external
+    `c_func` calls runtime-only unless a future compiler intrinsic explicitly models
+    their behavior
+  - immutable locals/globals with comptime-known initializers may feed comptime
+    evaluation; runtime-dependent values remain invalid in comptime contexts
+  - no runtime side effects during comptime evaluation
 
 28. brolang build system (requires comptime execution)
 
@@ -1244,9 +1266,10 @@ data :: read_file(path) catch |e| match e {
 
 ```
 make_array func($N usize) [N]u8 { ... }  # implemented: integer comptime value params
-max func($T type, a, b T) T { ... }      # deferred: comptime type params
+max func($T type, a, b T) T { ... }      # implemented: comptime type params
-$x :: 32                                 # deferred: comptime evaluable constant
+x :: $32                                 # implemented: force comptime expression evaluation
-$sum func(a, b int) int { ... }          # deferred: comptime evaluable function
+n :: $sum(1, 2)                          # implemented: ordinary functions can run at comptime
+res :: ${ yield 4 }                      # implemented: comptime value block
 ```
 
 ## A word on memory allocation

compiler/ast/ast.odin

@@ -85,6 +85,7 @@ Expr_Kind :: enum u8 {
 	Struct_Literal,
 	Keyed,
 	Cast,
+	Comptime,
 	Negate,
 	Not,
 	Add,

compiler/checker/checker.odin

@@ -389,6 +389,7 @@ eval_integer_constant_in_context :: proc(
 	pkg: ast.Package_Id,
 	file: ast.File_Id,
 	depth := 0,
+	values: []Comptime_Value = nil,
 ) -> Constant {
 	if depth > 64 || expr_id == ast.INVALID_EXPR || int(expr_id) >= len(checker.ast_module.exprs) {
 		return Constant{kind = .Not_Constant}
@@ -397,8 +398,15 @@ eval_integer_constant_in_context :: proc(
 	#partial switch expr.kind {
 	case .Integer:
 		return Constant{kind = .Value, value = i128(expr.integer)}
+	case .Bool:
+		return Constant{kind = .Value, value = i128(expr.integer)}
 	case .Name:
 		if !symbol.is_valid(expr.qualifier) {
+			if value, ok := find_comptime_value(values, expr.name); ok {
+				if value.kind == .Integer {
+					return Constant{kind = .Value, value = value.value}
+				}
+			}
 			if value, ok := current_comptime_value(checker, expr.name); ok {
 				if value.kind == .Integer {
 					return Constant{kind = .Value, value = value.value}
@@ -417,17 +425,32 @@ eval_integer_constant_in_context :: proc(
 		if g.external || !g.immutable {
 			return Constant{kind = .Not_Constant}
 		}
-		return eval_integer_constant_in_context(checker, g.expr, g.pkg, g.file, depth+1)
+		return eval_integer_constant_in_context(checker, g.expr, g.pkg, g.file, depth+1, values)
+	case .Comptime:
+		if expr.left != ast.INVALID_EXPR {
+			return eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1, values)
+		}
+		result, produced, ok := eval_comptime_statements(checker, expr.body, pkg, file, depth+1, values, true)
+		if ok && produced {
+			return result
+		}
+		return Constant{kind = .Not_Constant}
 	case .Negate:
-		operand := eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1)
+		operand := eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1, values)
 		if operand.kind == .Value {
 			value, overflow := intrinsics.overflow_sub(i128(0), operand.value)
 			return Constant{kind = .Overflow} if overflow else Constant{kind = .Value, value = value}
 		}
 		return operand
+	case .Not:
+		operand := eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1, values)
+		if operand.kind == .Value {
+			return Constant{kind = .Value, value = 1 if operand.value == 0 else 0}
+		}
+		return operand
 	case .Add, .Sub, .Mul, .Div:
-		left := eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1)
+		left := eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1, values)
-		right := eval_integer_constant_in_context(checker, expr.right, pkg, file, depth+1)
+		right := eval_integer_constant_in_context(checker, expr.right, pkg, file, depth+1, values)
 		if left.kind == .Div_By_Zero || right.kind == .Div_By_Zero {
 			return Constant{kind = .Div_By_Zero}
 		}
@@ -453,8 +476,161 @@ eval_integer_constant_in_context :: proc(
 			value, overflow = intrinsics.overflow_add(left.value, right.value)
 		}
 		return Constant{kind = .Overflow} if overflow else Constant{kind = .Value, value = value}
+	case .Eq, .Ne, .Lt, .Le, .Gt, .Ge:
+		left := eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1, values)
+		right := eval_integer_constant_in_context(checker, expr.right, pkg, file, depth+1, values)
+		if left.kind != .Value || right.kind != .Value {
+			if left.kind == .Div_By_Zero || right.kind == .Div_By_Zero {
+				return Constant{kind = .Div_By_Zero}
+			}
+			if left.kind == .Overflow || right.kind == .Overflow {
+				return Constant{kind = .Overflow}
 			}
 			return Constant{kind = .Not_Constant}
+		}
+		ok := false
+		#partial switch expr.kind {
+		case .Eq: ok = left.value == right.value
+		case .Ne: ok = left.value != right.value
+		case .Lt: ok = left.value < right.value
+		case .Le: ok = left.value <= right.value
+		case .Gt: ok = left.value > right.value
+		case .Ge: ok = left.value >= right.value
+		}
+		return Constant{kind = .Value, value = 1 if ok else 0}
+	case .And, .Or:
+		left := eval_integer_constant_in_context(checker, expr.left, pkg, file, depth+1, values)
+		if left.kind != .Value {
+			return left
+		}
+		if expr.kind == .And && left.value == 0 {
+			return Constant{kind = .Value, value = 0}
+		}
+		if expr.kind == .Or && left.value != 0 {
+			return Constant{kind = .Value, value = 1}
+		}
+		right := eval_integer_constant_in_context(checker, expr.right, pkg, file, depth+1, values)
+		if right.kind == .Value {
+			return Constant{kind = .Value, value = 1 if right.value != 0 else 0}
+		}
+		return right
+	case .Call:
+		return eval_comptime_call(checker, expr, pkg, file, depth+1, values)
+	}
+	return Constant{kind = .Not_Constant}
+}
+
+eval_comptime_statements :: proc(
+	checker: ^Checker,
+	statements: []ast.Stmt_Id,
+	pkg: ast.Package_Id,
+	file: ast.File_Id,
+	depth: int,
+	values: []Comptime_Value,
+	yield_returns: bool,
+) -> (Constant, bool, bool) {
+	env: [dynamic]Comptime_Value
+	env.allocator = checker.allocator
+	append(&env, ..values)
+	defer delete(env)
+	for statement_id in statements {
+		if statement_id == ast.INVALID_STMT || int(statement_id) >= len(checker.ast_module.statements) {
+			return Constant{kind=.Not_Constant}, false, false
+		}
+		statement := checker.ast_module.statements[statement_id]
+		#partial switch statement.kind {
+		case .Declaration:
+			if statement.expr == ast.INVALID_EXPR || !statement.immutable {
+				return Constant{kind=.Not_Constant}, false, false
+			}
+			value := eval_integer_constant_in_context(checker, statement.expr, pkg, file, depth+1, env[:])
+			if value.kind != .Value || statement.name == checker.sink_symbol {
+				return value, false, false
+			}
+			append(&env, Comptime_Value{name=statement.name, type=types.I64, value=value.value})
+		case .Return:
+			if yield_returns || statement.expr == ast.INVALID_EXPR {
+				return Constant{kind=.Not_Constant}, false, false
+			}
+			value := eval_integer_constant_in_context(checker, statement.expr, pkg, file, depth+1, env[:])
+			return value, value.kind == .Value, value.kind == .Value
+		case .Yield:
+			if !yield_returns || statement.expr == ast.INVALID_EXPR {
+				return Constant{kind=.Not_Constant}, false, false
+			}
+			value := eval_integer_constant_in_context(checker, statement.expr, pkg, file, depth+1, env[:])
+			return value, value.kind == .Value, value.kind == .Value
+		case .If:
+			if len(statement.captures) > 0 || statement.guard != ast.INVALID_EXPR {
+				return Constant{kind=.Not_Constant}, false, false
+			}
+			condition := eval_integer_constant_in_context(checker, statement.expr, pkg, file, depth+1, env[:])
+			if condition.kind != .Value {
+				return condition, false, false
+			}
+			body := statement.body if condition.value != 0 else statement.else_body
+			value, produced, ok := eval_comptime_statements(checker, body, pkg, file, depth+1, env[:], yield_returns)
+			if !ok || produced {
+				return value, produced, ok
+			}
+		case:
+			return Constant{kind=.Not_Constant}, false, false
+		}
+	}
+	return Constant{kind=.Not_Constant}, false, true
+}
+
+eval_comptime_call :: proc(
+	checker: ^Checker,
+	expr: ast.Expr,
+	pkg: ast.Package_Id,
+	file: ast.File_Id,
+	depth: int,
+	values: []Comptime_Value,
+) -> Constant {
+	if expr.left != ast.INVALID_EXPR || depth > 64 {
+		return Constant{kind=.Not_Constant}
+	}
+	target_pkg, available := expr_package(checker, expr, pkg, file, false)
+	if !available {
+		return Constant{kind=.Not_Constant}
+	}
+	template := find_template(checker, expr.name, target_pkg)
+	if template == ast.INVALID_FUNCTION || int(template) >= len(checker.ast_module.functions) {
+		return Constant{kind=.Not_Constant}
+	}
+	function := checker.ast_module.functions[template]
+	if function.c_abi || !function.has_body || types.is_valid(function.error) ||
+	   len(function.unsupported_reason) > 0 || !valid_call_arity(function, len(expr.args)) {
+		return Constant{kind=.Not_Constant}
+	}
+	comptime_values, comptime_ok := collect_comptime_values(checker, function, expr.args, pkg, file, false, values)
+	defer delete(comptime_values, checker.allocator)
+	if !comptime_ok {
+		return Constant{kind=.Not_Constant}
+	}
+	env: [dynamic]Comptime_Value
+	env.allocator = checker.allocator
+	defer delete(env)
+	append(&env, ..comptime_values)
+	for param, index in function.params {
+		if param.comptime_value {
+			continue
+		}
+		if index >= len(expr.args) {
+			return Constant{kind=.Not_Constant}
+		}
+		value := eval_integer_constant_in_context(checker, expr.args[index], pkg, file, depth+1, values)
+		if value.kind != .Value {
+			return value
+		}
+		append(&env, Comptime_Value{name=param.name, type=types.I64, value=value.value})
+	}
+	result, produced, ok := eval_comptime_statements(checker, function.body, function.pkg, function.file, depth+1, env[:], false)
+	if !ok || !produced {
+		return Constant{kind=.Not_Constant}
+	}
+	return result
 }
 
 fits_signed_type :: proc(value: i128, value_type: types.Type, selected := target.DEFAULT) -> bool {
@@ -952,6 +1128,7 @@ collect_comptime_values :: proc(
 	pkg: ast.Package_Id,
 	file: ast.File_Id,
 	diagnose := false,
+	extra_values: []Comptime_Value = nil,
 ) -> ([]Comptime_Value, bool) {
 	if !function_has_comptime_params(function) {
 		return nil, true
@@ -1002,7 +1179,7 @@ collect_comptime_values :: proc(
 		}
 		constant := Constant{kind = .Not_Constant}
 		if index < len(args) {
-			constant = eval_integer_constant_in_context(checker, args[index], pkg, file)
+			constant = eval_integer_constant_in_context(checker, args[index], pkg, file, values=extra_values)
 		}
 		if constant.kind != .Value {
 			if diagnose {
@@ -1145,6 +1322,11 @@ mark_expr_imports_used :: proc(checker: ^Checker, expr_id: ast.Expr_Id, file: as
 			}
 		case .Negate, .Not, .Address, .Deref, .Field, .Unwrap, .Try, .Keyed, .Enum_Literal, .Cast:
 			append(&stack, expr.left)
+		case .Comptime:
+			if expr.left != ast.INVALID_EXPR {
+				append(&stack, expr.left)
+			}
+			mark_block_imports_used(checker, expr.body, file)
 		case .Catch:
 			append(&stack, expr.left)
 			if expr.right != ast.INVALID_EXPR {
@@ -1744,6 +1926,25 @@ infer_compound_expr :: proc(
 ) -> types.Type {
 	store := &checker.module.types
 	#partial switch expr.kind {
+	case .Comptime:
+		constant := Constant{kind=.Not_Constant}
+		if expr.left != ast.INVALID_EXPR {
+			constant = eval_integer_constant_in_context(checker, expr.left, pkg, file)
+		}
+		if expr.left == ast.INVALID_EXPR {
+			value, produced, ok := eval_comptime_statements(checker, expr.body, pkg, file, 0, nil, true)
+			if ok && produced {
+				constant = value
+			}
+		}
+		if constant.kind == .Overflow || constant.kind == .Div_By_Zero ||
+		   (constant.kind == .Value && !fits_i64(constant.value)) {
+			return types.I64
+		}
+		if constant.kind == .Value {
+			return types.smallest_signed_for_literal(i64(constant.value))
+		}
+		return types.INVALID
 	case .Bool:
 		return types.BOOL
 	case .Not:
@@ -1954,7 +2155,7 @@ infer_expr :: proc(
 				_ = pop(&stack)
 			case .String, .Array, .None, .Undefined, .Address, .Deref, .Index, .Slice,
 			     .Field, .Unwrap, .Orelse, .Try, .Catch, .Struct_Literal, .Keyed, .Enum_Literal, .Cast,
-			     .Bool, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range:
+			     .Comptime, .Bool, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range:
 				last = infer_compound_expr(checker, expr, locals, pkg, file, demanded, local_types)
 				_ = pop(&stack)
 			case .Name:
@@ -2371,7 +2572,7 @@ infer_statements :: proc(
 			open_float := false
 			const_val := i128(0)
 			if !is_runtime_type(checker, declared_local) && !is_undefined_expr(checker, statement.expr) {
-				constant := eval_constant(checker, statement.expr)
+				constant := eval_integer_constant_in_context(checker, statement.expr, pkg, file)
 				if constant.kind == .Value && fits_i64(constant.value) {
 					open = true
 					const_val = constant.value
@@ -2842,7 +3043,7 @@ expr_accepts_numeric_demand :: proc(
 	   expr_id == ast.INVALID_EXPR || int(expr_id) >= len(checker.ast_module.exprs) {
 		return false
 	}
-	if constant := eval_constant(checker, expr_id); constant.kind == .Value {
+	if constant := eval_integer_constant_in_context(checker, expr_id, pkg, file); constant.kind == .Value {
 		return open_integer_accepts_demand(checker, constant.value, demand)
 	}
 	if is_float_constant_expr(checker, expr_id) {
@@ -2945,7 +3146,7 @@ infer_all :: proc(checker: ^Checker) {
 		if global.external {
 			continue
 		}
-		constant := eval_constant(checker, global.expr)
+		constant := eval_integer_constant_in_context(checker, global.expr, global.pkg, global.file)
 		if constant.kind == .Value && fits_i64(constant.value) {
 			checker.global_open_const[index] = true
 			checker.global_const_value[index] = constant.value
@@ -4120,6 +4321,21 @@ build_compound_expr :: proc(
 			target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
 			diagnostic=source.INVALID_DIAGNOSTIC,
 		})
+	case .Comptime:
+		constant := Constant{kind=.Not_Constant}
+		if expr.left != ast.INVALID_EXPR {
+			constant = eval_integer_constant_in_context(checker, expr.left, pkg, file)
+		} else {
+			value, produced, ok := eval_comptime_statements(checker, expr.body, pkg, file, 0, nil, true)
+			if ok && produced {
+				constant = value
+			}
+		}
+		if constant.kind == .Value || constant.kind == .Overflow || constant.kind == .Div_By_Zero {
+			return build_constant_expr(checker, expr, constant, expected)
+		}
+		id := source.add(checker.diagnostics, expr.span, "expression cannot be evaluated at comptime")
+		return invalid_hir_expr(checker, expr.span, id)
 	case .Bool:
 		return add_hir_expr(checker, hir.Expr{
 			kind=.Bool, span=expr.span, type=types.BOOL, integer=i64(expr.integer),
@@ -4400,7 +4616,7 @@ build_expr :: proc(
 			switch expr.kind {
 			case .String, .Array, .None, .Undefined, .Address, .Deref, .Index, .Slice,
 			     .Field, .Unwrap, .Orelse, .Try, .Catch, .Struct_Literal, .Keyed,
-			     .Bool, .Cast, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range,
+			     .Bool, .Cast, .Comptime, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or, .Range,
 			     .Enum_Literal:
 				last = build_compound_expr(
 					checker, expr, locals, global_reads, calls, frame.expected, pkg, file,
@@ -5092,7 +5308,7 @@ build_block :: proc(
 			// `undefined`, open numeric constants, or arithmetic expressions.
 			open_const_decl := !is_runtime_type(checker, declared) && !is_undefined_expr(checker, statement.expr)
 			if open_const_decl {
-				constant := eval_constant(checker, statement.expr)
+				constant := eval_integer_constant_in_context(checker, statement.expr, ctx.pkg, ctx.file)
 				open_const_decl = constant.kind == .Value && fits_i64(constant.value) ||
 				                  is_float_constant_expr(checker, statement.expr)
 			}
@@ -7650,7 +7866,7 @@ build_globals :: proc(checker: ^Checker) {
 		expected := types.INVALID
 		if is_runtime_type(checker, declared) {
 			expected = declared
-		} else if constant := eval_constant(checker, global.expr);
+		} else if constant := eval_integer_constant_in_context(checker, global.expr, global.pkg, global.file);
 		   constant.kind == .Value && fits_i64(constant.value) &&
 		   is_runtime_type(checker, checker.global_types[global_index]) {
 			// Open integer constant: build against its demanded/defaulted type. Gated

compiler/parser/parser.odin

@@ -914,7 +914,7 @@ is_simple_range_bound :: proc(expr: ast.Expr) -> bool {
 
 prefix_binding_power :: proc(kind: token.Kind) -> (right: int, ok: bool) {
 	#partial switch kind {
-	case .Minus, .Ampersand, .Bang, .Keyword_Try:
+	case .Minus, .Ampersand, .Bang, .Dollar, .Keyword_Try:
 		return 20, true
 	}
 	return 0, false
@@ -931,6 +931,18 @@ parse_expression_bp :: proc(parser: ^Parser, minimum_binding_power, nesting: int
 	left := ast.INVALID_EXPR
 	if right_power, ok := prefix_binding_power(current(parser).kind); ok {
 		operator := advance(parser)
+		if operator.kind == .Dollar && current(parser).kind == .Left_Brace {
+			body := parse_block(parser)
+			end := previous(parser)
+			left = add_expr(parser, ast.Expr{
+				kind = .Comptime,
+				span = span_from(operator.span, end.span),
+				body = body,
+				left = ast.INVALID_EXPR,
+				right = ast.INVALID_EXPR,
+				diagnostic = source.INVALID_DIAGNOSTIC,
+			})
+		} else {
 			if parser.delimiter_depth > 0 {
 				skip_newlines(parser)
 			}
@@ -940,15 +952,17 @@ parse_expression_bp :: proc(parser: ^Parser, minimum_binding_power, nesting: int
 			#partial switch operator.kind {
 			case .Ampersand:   prefix_kind = .Address
 			case .Bang:        prefix_kind = .Not
+			case .Dollar:      prefix_kind = .Comptime
 			case .Keyword_Try: prefix_kind = .Try
 			}
 			left = add_expr(parser, ast.Expr{
-			kind=prefix_kind,
+				kind = prefix_kind,
-			span=span_from(operator.span, operand_expr.span),
+				span = span_from(operator.span, operand_expr.span),
-			left=operand,
+				left = operand,
-			right=ast.INVALID_EXPR,
+				right = ast.INVALID_EXPR,
-			diagnostic=source.INVALID_DIAGNOSTIC,
+				diagnostic = source.INVALID_DIAGNOSTIC,
 			})
+		}
 	} else {
 		left = parse_primary(parser, nesting)
 	}

compiler_tests.odin

@@ -567,6 +567,42 @@ main func() void {}
 	testing.expect_value(t, module.exprs[chained.left].kind, ast.Expr_Kind.Negate)
 }
 
+@(test)
+parser_accepts_comptime_prefix_and_block_expressions :: proc(t: ^testing.T) {
+	text := `sum func(a, b int) int { return a + b }
+literal :: $32
+call :: $sum(1, 2) + 3
+block :: ${
+	yield 4
+}
+main func() void {}
+`
+	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)
+	module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&module)
+
+	literal := module.exprs[module.globals[0].expr]
+	call_add := module.exprs[module.globals[1].expr]
+	call := module.exprs[call_add.left]
+	block := module.exprs[module.globals[2].expr]
+
+	testing.expect_value(t, len(diagnostics.items), 0)
+	testing.expect_value(t, literal.kind, ast.Expr_Kind.Comptime)
+	testing.expect_value(t, module.exprs[literal.left].kind, ast.Expr_Kind.Integer)
+	testing.expect_value(t, call_add.kind, ast.Expr_Kind.Add)
+	testing.expect_value(t, call.kind, ast.Expr_Kind.Comptime)
+	testing.expect_value(t, module.exprs[call.left].kind, ast.Expr_Kind.Call)
+	testing.expect_value(t, block.kind, ast.Expr_Kind.Comptime)
+	testing.expect_value(t, len(block.body), 1)
+	testing.expect_value(t, module.statements[block.body[0]].kind, ast.Stmt_Kind.Yield)
+}
+
 nested_expression_source :: proc(call: bool, depth: int) -> string {
 	builder := strings.builder_make()
 	defer strings.builder_destroy(&builder)
@@ -2235,6 +2271,119 @@ main func() void {
 	testing.expect(t, found_assign)
 }
 
+@(test)
+comptime_expression_forces_integer_evaluation :: proc(t: ^testing.T) {
+	text := `sum func(a, b int) int {
+	return a + b
+}
+max func(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+nested func(value int) int {
+	two :: 2
+	return sum(value, two)
+}
+make_array func($N usize) [N]u8 {
+	data [N]u8 = undefined
+	return data
+}
+forced :: $sum(1, 2)
+main func() i32 {
+	value i32 :: $sum(20, 22)
+	choice i32 :: $max(9, 3)
+	blocked i32 :: ${
+		local :: 5
+		yield sum(local, 6)
+	}
+	bytes [_]u8 :: make_array($nested(2))
+	if forced != 3 {
+		return 1
+	}
+	if value != 42 {
+		return 2
+	}
+	if choice != 9 {
+		return 3
+	}
+	if blocked != 11 {
+		return 4
+	}
+	if bytes.len != 4 {
+		return 5
+	}
+	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)
+	testing.expect(t, strings.contains(llvm_text, "@bro.g.0 = internal constant i8 3"))
+}
+
+@(test)
+comptime_expression_diagnoses_unsupported_v1_evaluation :: proc(t: ^testing.T) {
+	text := `loop func() int {
+	while true {
+		return 1
+	}
+	return 0
+}
+missing func() int {
+	if true {
+	}
+}
+recurse func(value int) int {
+	return recurse(value)
+}
+main func() void {
+	runtime i32 = 1
+	_ = $runtime
+	_ = $loop()
+	_ = $missing()
+	_ = $recurse(1)
+	_ = ${
+		value :: 1
+	}
+}
+`
+	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)
+
+	found := 0
+	for diagnostic in diagnostics.items {
+		if strings.contains(diagnostic.message, "expression cannot be evaluated at comptime") {
+			found += 1
+		}
+	}
+	testing.expect(t, found >= 5)
+}
+
 @(test)
 unused_function_signatures_are_validated_eagerly :: proc(t: ^testing.T) {
 	text := `broken func(value, value i8, nope void) void {}
@@ -5615,6 +5764,16 @@ comptime_type_params_compile_and_run :: proc(t: ^testing.T) {
 	testing.expect_value(t, state.exit_code, 0)
 }
 
+@(test)
+comptime_eval_compile_and_run :: proc(t: ^testing.T) {
+	output := "/tmp/brolang-test-comptime-eval"
+	defer _ = os.remove(output)
+	status := compiler_core.compile_package("examples/programs/comptime_eval", output)
+	testing.expect_value(t, status, 0)
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 0)
+}
+
 @(test)
 lazy_function_body_marks_import_as_used_without_resolving_it :: proc(t: ^testing.T) {
 	output := "/tmp/brolang-test-package-lazy-import"

examples/programs/comptime_eval/main.bro

@@ -0,0 +1,49 @@
+sum func(a, b int) int {
+	return a + b
+}
+
+max func(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+nested func(value int) int {
+	two :: 2
+	return sum(value, two)
+}
+
+make_array func($N usize) [N]u8 {
+	data [N]u8 = undefined
+	return data
+}
+
+forced :: $sum(1, 2)
+
+main func() i32 {
+	value i32 :: $sum(20, 22)
+	choice i32 :: $max(9, 3)
+	blocked i32 :: ${
+		local :: 5
+		yield sum(local, 6)
+	}
+	bytes [_]u8 :: make_array($nested(2))
+
+	if forced != 3 {
+		return 1
+	}
+	if value != 42 {
+		return 2
+	}
+	if choice != 9 {
+		return 3
+	}
+	if blocked != 11 {
+		return 4
+	}
+	if bytes.len != 4 {
+		return 5
+	}
+	return 0
+}