add range constraint type

TODO.md

@@ -181,19 +181,26 @@
   - disallow: `b :: undefined` since assigning undefined to something that can't change defeats the purpose
   - disallow assigning `undefined` after declaration; use optionals and `none` for values that intentionally move back to an empty state
 
-13. introduce a `float` type constraint (similar to `int`) (implemented)
-  - resolves a local binding to any float scalar (`f32`/`f64`) via static analysis; widens
-    `f32` -> `f64` across assignments, mirroring how `int` picks the smallest fitting integer
+13. introduce `float` and `range` type constraints (the `int` family generalized) (implemented)
+  - `float` resolves a local binding to any float scalar (`f32`/`f64`) via static analysis;
+    widens `f32` -> `f64` across assignments, mirroring how `int` picks the smallest integer
   - on a local declaration, integer literals satisfy `float` and default to `f64`
     (`pi float = 3` is `3.0`); a runtime integer (`x float = some_i32`) stays a
     `cannot implicitly convert` error
-  - a local initializer whose numeric family doesn't satisfy the constraint now errors for
-    both `int` and `float` instead of silently taking the initializer's natural type
-  - as with `int`, a constraint in a param/result position is a generic passthrough (it
-    forwards the inferred type unchanged, e.g. an identity `func(v int) int` over a range),
-    so the literal-as-float and family checks apply to local bindings, not passthroughs
+  - `range` is now a spellable type/constraint: `r range :: 0..10` resolves to the inferred
+    range (element type preserved), and `func(start, end int) range { return start..end }`
+    monomorphizes the result per call. this replaces the prior `int`-as-passthrough hack that
+    was the only way to forward a range through a function
+  - `int`/`float`/`range` constraints now gate by family in every position (previously
+    params/results were unchecked generic passthroughs):
+    - a local initializer out of family errors instead of silently taking the natural type
+    - a param rejects an out-of-family argument (`cannot pass f64 to 'int' parameter 'x'`);
+      a `float` param accepts an integer-literal argument as f64 (e.g. `f(3)`)
+    - a function result is narrowed to the constraint's family
 
-14. add slice-by-range
+14. broaden type inference to surrounding context
+
+15. add slice-by-range
   - allow the use of a range in slice expressions:
     ```
     excl_range range :: 0..10
@@ -203,8 +210,6 @@
     some_arr[incl_range] # slice by named inclusive range
     ```
 
-15. broaden type inference from surrounding context
-
 ## A word on multi-unwrap
 
 Unwrap multiple optionals with `and`. This **short-circuits**: if the first optional is none, subsequent expressions are not evaluated.

compiler/checker/checker.odin

@@ -538,7 +538,14 @@ call_arg_expected :: proc(function: ast.Function, index: int) -> types.Type {
 	if index < 0 || index >= len(function.params) {
 		return types.INVALID
 	}
-	return type_from_syntax(function.params[index].type)
+	declared := type_from_syntax(function.params[index].type)
+	// A `float` param defaults to f64 so an integer-literal argument builds as a
+	// float constant (e.g. `f(3)` -> 3.0), mirroring `pi float = 3` for locals.
+	// `int`/`range` constraints have no single default and keep building naturally.
+	if declared == types.FLOAT {
+		return types.F64
+	}
+	return declared
 }
 
 callable_arg_expected :: proc(function_type: types.Type, function_item: types.Node, store: ^types.Store, index: int) -> types.Type {
@@ -994,7 +1001,7 @@ find_spec :: proc(checker: ^Checker, template: ast.Function_Id, actual_args: []t
 			if param_index < len(actual_args) {
 				actual = actual_args[param_index]
 			}
-			if !types.equal(spec.args[param_index], specialized_param_type(param.type, actual)) {
+			if !types.equal(spec.args[param_index], specialized_param_type(checker, param.type, actual)) {
 				matches = false
 				break
 			}
@@ -1006,10 +1013,14 @@ find_spec :: proc(checker: ^Checker, template: ast.Function_Id, actual_args: []t
 	return INVALID_SPEC
 }
 
-specialized_param_type :: proc(syntax: ast.Type_Syntax, actual: types.Type) -> types.Type {
+// specialized_param_type maps a parameter's declared type to its monomorphized
+// type for a given actual argument. A constraint param (`int`/`float`/`range`)
+// resolves to the actual's family member (INVALID if out of family), so a call
+// passing an out-of-family argument fails to specialize and is rejected.
+specialized_param_type :: proc(checker: ^Checker, syntax: ast.Type_Syntax, actual: types.Type) -> types.Type {
 	declared := type_from_syntax(syntax)
 	if types.is_constraint(declared) {
-		return actual
+		return types.constraint_target(declared, actual, &checker.module.types)
 	}
 	return declared
 }
@@ -1020,7 +1031,7 @@ can_specialize :: proc(checker: ^Checker, function: ast.Function, actual_args: [
 		if index < len(actual_args) {
 			actual = actual_args[index]
 		}
-		if !is_runtime_type(checker, specialized_param_type(param.type, actual)) {
+		if !is_runtime_type(checker, specialized_param_type(checker, param.type, actual)) {
 			return false
 		}
 	}
@@ -1039,7 +1050,7 @@ ensure_spec :: proc(checker: ^Checker, template: ast.Function_Id, actual_args: [
 		if index < len(actual_args) {
 			actual = actual_args[index]
 		}
-		append(&signature, specialized_param_type(param.type, actual))
+		append(&signature, specialized_param_type(checker, param.type, actual))
 	}
 	result := type_from_syntax(function.result)
 	if function.pkg == 0 && function.name == checker.main_symbol && function.result == types.INT {
@@ -1541,7 +1552,7 @@ merge_infer_local_type :: proc(
 		return false
 	}
 	if types.is_constraint(local.declared) {
-		if !types.constraint_accepts(local.declared, inferred) {
+		if !types.constraint_accepts(local.declared, inferred, &checker.module.types) {
 			return false
 		}
 		if !is_runtime_type(checker, local.type) {
@@ -1553,7 +1564,7 @@ merge_infer_local_type :: proc(
 			return false
 		}
 		merged := types.widest(local.type, inferred)
-		if types.constraint_accepts(local.declared, merged) {
+		if types.constraint_accepts(local.declared, merged, &checker.module.types) {
 			local.type = merged
 			record_infer_local_type(local^, local_types)
 			return true
@@ -1608,7 +1619,7 @@ infer_statements :: proc(
 			} else if types.is_constraint(declared_local) {
 				// Seed the binding in-family (INVALID on mismatch, which
 				// build_block reports). FLOAT defaults integers to f64.
-				value_type = types.constraint_target(declared_local, value_type)
+				value_type = types.constraint_target(declared_local, value_type, &checker.module.types)
 			}
 			local := Infer_Local{
 				name=statement.name,
@@ -1753,10 +1764,10 @@ infer_spec_locals_and_result :: proc(
 	result := types.INVALID
 	infer_statements(checker, function.body, &locals, local_types, function.pkg, function.file, demanded, &result, result_hint)
 	if types.is_constraint(declared) {
-		// Params/results use a constraint as a generic passthrough (e.g. an
-		// identity `func(v int) int` forwarding a range), so the result keeps
-		// the inferred type as-is rather than being narrowed to the family.
-		return local_types, result
+		// Narrow the inferred result to the constraint's family; an out-of-family
+		// result (e.g. returning a non-integer from an `int` function) yields
+		// INVALID and is rejected downstream.
+		return local_types, types.constraint_target(declared, result, &checker.module.types)
 	}
 	return local_types, declared
 }
@@ -3230,9 +3241,37 @@ build_expr :: proc(
 					continue
 				}
 			}
+			arg_violation := source.INVALID_DIAGNOSTIC
+			{
+				params := checker.ast_module.functions[frame.template].params
+				for index in 0..<len(params) {
+					if index >= len(stack[frame_index].arg_types) {
+						break
+					}
+					declared := type_from_syntax(params[index].type)
+					actual := stack[frame_index].arg_types[index]
+					if types.is_constraint(declared) && types.is_valid(actual) &&
+					   !types.is_valid(types.constraint_target(declared, actual, &checker.module.types)) {
+						arg_violation = source.addf(
+							checker.diagnostics, expr.span,
+							"cannot pass %s to '%s' parameter '%s'",
+							types.name(actual), types.name(declared),
+							symbol_text(checker, params[index].name),
+						)
+						break
+					}
+				}
+			}
 			spec := find_spec(checker, frame.template, stack[frame_index].arg_types)
 			delete(stack[frame_index].arg_types, checker.allocator)
 			stack[frame_index].arg_types = nil
+			if arg_violation != source.INVALID_DIAGNOSTIC {
+				delete(stack[frame_index].built_args, checker.allocator)
+				stack[frame_index].built_args = nil
+				last = invalid_hir_expr(checker, expr.span, arg_violation)
+				_ = pop(&stack)
+				continue
+			}
 			if spec == INVALID_SPEC {
 				id := source.addf(
 					checker.diagnostics,

compiler/lexer/lexer.odin

@@ -39,6 +39,7 @@ keyword_kind :: proc(text: string) -> token.Kind {
 	case "bool":          return .Keyword_Bool
 	case "int":           return .Keyword_Int
 	case "float":         return .Keyword_Float
+	case "range":         return .Keyword_Range
 	case "i8":            return .Keyword_I8
 	case "i16":           return .Keyword_I16
 	case "i32":           return .Keyword_I32

compiler/parser/parser.odin

@@ -89,7 +89,7 @@ invalid_expr :: proc(parser: ^Parser, span: source.Span, message: string) -> ast
 
 is_type_token :: proc(kind: token.Kind) -> bool {
 	#partial switch kind {
-	case .Keyword_Int, .Keyword_Float, .Keyword_I8, .Keyword_I16, .Keyword_I32, .Keyword_I64,
+	case .Keyword_Int, .Keyword_Float, .Keyword_Range, .Keyword_I8, .Keyword_I16, .Keyword_I32, .Keyword_I64,
 	     .Keyword_U8, .Keyword_U16, .Keyword_U32, .Keyword_U64,
 	     .Keyword_Isize, .Keyword_Usize, .Keyword_F32, .Keyword_F64,
 	     .Keyword_C_Char, .Keyword_C_Schar, .Keyword_C_Uchar,
@@ -219,6 +219,9 @@ parse_type :: proc(parser: ^Parser) -> ast.Type_Syntax {
 	case .Keyword_Float:
 		advance(parser)
 		return types.FLOAT
+	case .Keyword_Range:
+		advance(parser)
+		return types.RANGE
 	case .Keyword_I8:
 		advance(parser)
 		return types.I8

compiler/token/token.odin

@@ -73,6 +73,7 @@ Kind :: enum u8 {
 	Keyword_Bool,
 	Keyword_Int,
 	Keyword_Float,
+	Keyword_Range,
 	Keyword_I8,
 	Keyword_I16,
 	Keyword_I32,

compiler/types/types.odin

@@ -42,6 +42,7 @@ C_LONGDOUBLE :: Type(28)
 
 BOOL :: Type(29)
 FLOAT :: Type(30)
+RANGE :: Type(31)
 
 DYNAMIC_START :: Type(64)
 
@@ -57,6 +58,7 @@ Kind :: enum u8 {
 	Void,
 	Int_Constraint,
 	Float_Constraint,
+	Range_Constraint,
 	Scalar,
 	Array,
 	Pointer,
@@ -299,6 +301,8 @@ kind :: proc(value: Type, store: ^Store = nil) -> Kind {
 		return .Int_Constraint
 	case FLOAT:
 		return .Float_Constraint
+	case RANGE:
+		return .Range_Constraint
 	case BOOL:
 		return .Scalar
 	}
@@ -338,15 +342,17 @@ is_bool :: proc(value: Type) -> bool {
 }
 
 is_constraint :: proc(value: Type) -> bool {
-	return value == INT || value == FLOAT
+	return value == INT || value == FLOAT || value == RANGE
 }
 
-// constraint_target reports the concrete type a constraint binding takes for an
-// inferred value, or INVALID if the value's numeric family is incompatible.
-// FLOAT accepts integers by defaulting them to f64: a constant integer becomes a
-// float literal in build_constant_expr, while a runtime integer then fails the
-// cross-family f64 coercion in coerce_expr (the intended mismatch error).
-constraint_target :: proc(constraint, inferred: Type) -> Type {
+// constraint_target reports the concrete type a constraint binding (local, or a
+// param/result monomorphized per call site) takes for an inferred value, or
+// INVALID if the value's family is incompatible. FLOAT accepts integers by
+// defaulting them to f64: a constant integer becomes a float literal in
+// build_constant_expr, while a runtime integer then fails the cross-family f64
+// coercion in coerce_expr (the intended mismatch error). RANGE accepts any range
+// type, keeping its inferred element type.
+constraint_target :: proc(constraint, inferred: Type, store: ^Store = nil) -> Type {
 	switch constraint {
 	case INT:
 		return inferred if is_concrete_integer(inferred) else INVALID
@@ -355,18 +361,22 @@ constraint_target :: proc(constraint, inferred: Type) -> Type {
 			return inferred
 		}
 		return F64 if is_concrete_integer(inferred) else INVALID
+	case RANGE:
+		return inferred if is_range(inferred, store) else INVALID
 	}
 	return INVALID
 }
 
-// constraint_accepts reports strict numeric-family membership, used when widening
-// a constraint binding across assignments (no integer-to-float defaulting here).
-constraint_accepts :: proc(constraint, concrete: Type) -> bool {
+// constraint_accepts reports strict family membership, used when widening a
+// constraint binding across assignments (no integer-to-float defaulting here).
+constraint_accepts :: proc(constraint, concrete: Type, store: ^Store = nil) -> bool {
 	switch constraint {
 	case INT:
 		return is_concrete_integer(concrete)
 	case FLOAT:
 		return is_float(concrete)
+	case RANGE:
+		return is_range(concrete, store)
 	}
 	return false
 }
@@ -1175,6 +1185,7 @@ name :: proc(value: Type) -> string {
 	case BOOL:          return "bool"
 	case INT:           return "int"
 	case FLOAT:         return "float"
+	case RANGE:         return "range"
 	case I8:            return "i8"
 	case I16:           return "i16"
 	case I32:           return "i32"

compiler_tests.odin

@@ -4841,7 +4841,7 @@ main :: func() i32 {
 
 @(test)
 equal_range_returns_infer_a_usable_result_type :: proc(t: ^testing.T) {
-	text := `choose :: func(first bool) int {
+	text := `choose :: func(first bool) range {
 	if first {
 		return 0..1
 	}
@@ -4886,10 +4886,10 @@ main :: func() i32 {
 
 @(test)
 for_loop_lowering_evaluates_once_and_avoids_index_bounds_checks :: proc(t: ^testing.T) {
-	text := `make_range :: func() int {
+	text := `make_range :: func() range {
 	return 0..2
 }
-make_array :: func() int {
+make_array :: func() [2]i32 {
 	return [1, 2]
 }
 main :: func() i32 {
@@ -5339,6 +5339,128 @@ main :: func() void {
 	testing.expect(t, found_convert_error)
 }
 
+@(test)
+range_constraint_local_resolves_to_inferred_range :: proc(t: ^testing.T) {
+	text := `make :: func() range {
+	r range :: 0..10
+	return r
+}
+main :: func() void {
+	_ = make()
+}
+`
+	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)
+
+	r_type, found := float_local_type(&hir_module, &symbols, "make", "r")
+	result_type, _ := float_result_type(&hir_module, &symbols, "make")
+
+	testing.expect_value(t, len(diagnostics.items), 0)
+	testing.expect(t, found)
+	testing.expect(t, types.is_range(r_type, &hir_module.types))
+	testing.expect_value(t, types.child_type(r_type, &hir_module.types), types.I8)
+	testing.expect(t, types.is_range(result_type, &hir_module.types))
+}
+
+@(test)
+range_constraint_param_and_result_monomorphize :: proc(t: ^testing.T) {
+	text := `pass :: func(r range) range {
+	return r
+}
+main :: func() void {
+	once :: 0..5
+	for pass(once) |v| {
+		_ = v
+	}
+}
+`
+	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)
+
+	result_type, found := float_result_type(&hir_module, &symbols, "pass")
+
+	testing.expect_value(t, len(diagnostics.items), 0)
+	testing.expect(t, found)
+	testing.expect(t, types.is_range(result_type, &hir_module.types))
+}
+
+@(test)
+int_param_rejects_float_argument :: proc(t: ^testing.T) {
+	text := `take :: func(x int) int {
+	return x
+}
+main :: func() void {
+	_ = take(1.5)
+}
+`
+	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_reject := false
+	for diagnostic in diagnostics.items {
+		found_reject = found_reject ||
+			strings.contains(diagnostic.message, "cannot pass f64 to 'int' parameter 'x'")
+	}
+
+	testing.expect(t, found_reject)
+}
+
+@(test)
+float_param_accepts_integer_literal_argument :: proc(t: ^testing.T) {
+	text := `take :: func(x float) float {
+	return x
+}
+main :: func() void {
+	y f64 = take(3)
+	_ = y
+}
+`
+	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)
+
+	result_type, found := float_result_type(&hir_module, &symbols, "take")
+
+	testing.expect_value(t, len(diagnostics.items), 0)
+	testing.expect(t, found)
+	testing.expect_value(t, result_type, types.F64)
+}
+
 @(test)
 undefined_accepts_concrete_runtime_annotations :: proc(t: ^testing.T) {
 	text := `Point :: struct {

examples/programs/for_loop/main.bro

@@ -1,6 +1,6 @@
 # Milestone 5: ranges and sequence for loops.
 
-pass :: func(value int) int {
+pass :: func(value range) range {
 	return value
 }
 

examples/programs/for_loop_edges/main.bro

@@ -1,4 +1,4 @@
-make_range :: func(calls @mut i32, end usize) int {
+make_range :: func(calls @mut i32, end usize) range {
 	calls^ = calls^ + 1
 	return 0..end
 }