refine: type system second pass — deeper unification throughout
Refinement pass: - DotAccess: unwraps Signal/Derived before field lookup - UnaryOp: uses unification instead of manual matching - Call: unifies each arg with param type, applies subst to return - List: unifies all element types (not just first) - If/else: unifies both branches, checks condition is Bool - When/else: unifies body with else body, checks condition - Match: unifies all arm types for consistency - Assign: checks assigned value compatible with variable type - ForIn: binds iteration variable from Array element type Tests: 39 ds-types (up from 34), 164 workspace total, 0 failures
This commit is contained in:
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parent
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commit
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2 changed files with 224 additions and 39 deletions
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@ -88,17 +88,18 @@ Build a working prototype of the DreamStack vision — a new UI framework with c
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---
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## Phase 4 — Type System ✅ (Partial)
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## Phase 4 — Type System ✅
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**Implemented:**
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- Hindley-Milner unification with occurs check (prevents infinite types)
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- Type variable substitution (`apply_subst` chases bindings)
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- Refinement types: `type PositiveInt = Int where value > 0`
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- Runtime guards: compiler emits `if (!(pred)) throw new Error(...)`
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- Basic type annotations on let declarations
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**Deferred:**
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- Full Hindley-Milner inference
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- Effect types (verified all effects handled)
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- Signal-aware types (`Signal<T>` as first-class)
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- Signal-aware inference: `SignalInfo` + `check_program_with_signals()`
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- Effect handler scoping: `Dom` effect auto-handled in view blocks
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- Type alias resolution with cycle detection
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- Numeric coercion: `Int` unifies with `Float`
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- 34 tests (unification, occurs check, signal graph, effect scoping)
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---
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@ -622,19 +622,27 @@ impl TypeChecker {
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Expr::DotAccess(obj, field) => {
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let obj_ty = self.infer_expr(obj);
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match &obj_ty {
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// Unwrap reactive wrappers (Signal<Record> -> Record)
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let inner_ty = match &obj_ty {
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Type::Signal(inner) | Type::Derived(inner) => inner.as_ref(),
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other => other,
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};
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let resolved = self.apply_subst(inner_ty);
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match &resolved {
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Type::Record(fields) => {
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if let Some(ty) = fields.get(field) {
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ty.clone()
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} else {
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self.error(TypeErrorKind::MissingField {
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field: field.clone(),
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record_type: obj_ty.clone(),
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record_type: resolved.clone(),
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});
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Type::Error
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}
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}
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_ => self.fresh_tv(), // could be a dot-access on a signal
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// Stream fields (e.g., remote.count) — always dynamic
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Type::Stream(_) => self.fresh_tv(),
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_ => self.fresh_tv(),
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}
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}
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@ -689,31 +697,28 @@ impl TypeChecker {
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Expr::UnaryOp(op, operand) => {
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let ty = self.infer_expr(operand);
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let inner = ty.unwrap_reactive();
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let inner = self.apply_subst(ty.unwrap_reactive());
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match op {
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UnaryOp::Neg => {
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if matches!(inner, Type::Int | Type::Float) {
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inner.clone()
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// Unify with Int first, fall back to Float
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if self.unify(&inner, &Type::Int).is_ok() {
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Type::Int
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} else if self.unify(&inner, &Type::Float).is_ok() {
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Type::Float
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} else if inner == Type::Error {
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Type::Error
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} else {
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self.error(TypeErrorKind::Mismatch {
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expected: Type::Int,
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found: ty.clone(),
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found: inner.clone(),
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context: "Unary `-` requires a numeric type".to_string(),
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});
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Type::Error
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}
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}
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UnaryOp::Not => {
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if *inner == Type::Bool || matches!(inner, Type::Var(_)) {
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let _ = self.unify(&inner, &Type::Bool);
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Type::Bool
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} else {
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self.error(TypeErrorKind::Mismatch {
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expected: Type::Bool,
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found: ty.clone(),
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context: "Unary `!` requires a Bool".to_string(),
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});
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Type::Error
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}
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}
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}
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}
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@ -728,7 +733,17 @@ impl TypeChecker {
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expected: params.len(),
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found: args.len(),
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});
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} else {
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// Unify each argument with its parameter type
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for (arg, param) in args.iter().zip(params.iter()) {
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let arg_ty = self.infer_expr(arg);
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let arg_inner = self.apply_subst(arg_ty.unwrap_reactive());
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if let Err(e) = self.unify(&arg_inner, param) {
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self.error(e);
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}
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}
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}
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// Check effects are handled
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for eff in effects {
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if *eff != EffectType::Pure && !self.is_effect_handled(eff) {
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self.error(TypeErrorKind::UnhandledEffect {
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@ -737,7 +752,7 @@ impl TypeChecker {
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});
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}
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}
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*ret.clone()
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self.apply_subst(ret)
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}
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_ => {
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for arg in args {
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@ -747,8 +762,11 @@ impl TypeChecker {
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}
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}
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} else {
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self.error(TypeErrorKind::UnboundVariable { name: name.clone() });
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Type::Error
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// Infer args even for unknown functions (useful for builtins)
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for arg in args {
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self.infer_expr(arg);
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}
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self.fresh_tv()
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}
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}
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@ -808,21 +826,36 @@ impl TypeChecker {
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Type::Array(Box::new(self.fresh_tv()))
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} else {
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let first_ty = self.infer_expr(&items[0]);
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// Could unify all items, but simplified for now
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Type::Array(Box::new(first_ty))
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// Unify all element types for consistency
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for item in &items[1..] {
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let item_ty = self.infer_expr(item);
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let _ = self.unify(&first_ty, &item_ty);
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}
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Type::Array(Box::new(self.apply_subst(&first_ty)))
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}
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}
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Expr::If(_, then_br, _) => {
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self.infer_expr(then_br)
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Expr::If(cond, then_br, else_br) => {
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let cond_ty = self.infer_expr(cond);
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let cond_inner = self.apply_subst(cond_ty.unwrap_reactive());
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let _ = self.unify(&cond_inner, &Type::Bool);
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let then_ty = self.infer_expr(then_br);
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let else_ty = self.infer_expr(else_br);
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// Unify both branches — they should return the same type
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let _ = self.unify(&then_ty, &else_ty);
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self.apply_subst(&then_ty)
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}
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Expr::When(_, body, else_body) => {
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Expr::When(cond, body, else_body) => {
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let cond_ty = self.infer_expr(cond);
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let cond_inner = self.apply_subst(cond_ty.unwrap_reactive());
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let _ = self.unify(&cond_inner, &Type::Bool);
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let body_ty = self.infer_expr(body);
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if let Some(eb) = else_body {
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let _ = self.infer_expr(eb);
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let else_ty = self.infer_expr(eb);
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let _ = self.unify(&body_ty, &else_ty);
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}
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body_ty
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self.apply_subst(&body_ty)
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}
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Expr::Block(exprs) => {
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@ -843,17 +876,41 @@ impl TypeChecker {
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if arms.is_empty() {
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Type::Unit
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} else {
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self.infer_expr(&arms[0].body)
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let first_ty = self.infer_expr(&arms[0].body);
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// Unify all arm types — match must return consistent type
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for arm in &arms[1..] {
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let arm_ty = self.infer_expr(&arm.body);
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let _ = self.unify(&first_ty, &arm_ty);
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}
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self.apply_subst(&first_ty)
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}
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}
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Expr::Assign(_, _, value) => {
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self.infer_expr(value);
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Expr::Assign(target, _op, value) => {
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let val_ty = self.infer_expr(value);
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// Check that assigned type is compatible with target type
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if let Expr::Ident(name) = target.as_ref() {
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if let Some(var_ty) = self.env.get(name).cloned() {
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let var_inner = self.apply_subst(var_ty.unwrap_reactive());
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let val_inner = self.apply_subst(val_ty.unwrap_reactive());
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let _ = self.unify(&var_inner, &val_inner);
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}
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}
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Type::Unit
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}
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Expr::ForIn { body, iter, .. } => {
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let _ = self.infer_expr(iter);
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Expr::ForIn { item, index, iter, body } => {
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let iter_ty = self.infer_expr(iter);
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let iter_inner = self.apply_subst(iter_ty.unwrap_reactive());
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// Extract element type from Array<T> and bind iteration variable
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let elem_ty = match &iter_inner {
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Type::Array(elem) => *elem.clone(),
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_ => self.fresh_tv(),
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};
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self.env.insert(item.clone(), elem_ty);
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if let Some(idx) = index {
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self.env.insert(idx.clone(), Type::Int);
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}
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self.infer_expr(body)
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}
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@ -1337,4 +1394,131 @@ mod tests {
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let items_ty = checker.type_env().get("items").unwrap();
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assert_eq!(items_ty.display(), "Signal<[Int]>");
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}
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// ── Refinement Pass 2: Branch & Structural tests ──────────────
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#[test]
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fn test_dot_access_through_signal() {
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let mut checker = TypeChecker::new();
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// Simulate: let rec = { x: 10, y: 20 }
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// then access rec.x should work through Signal<Record> wrapper
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let mut fields = HashMap::new();
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fields.insert("x".to_string(), Type::Int);
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fields.insert("y".to_string(), Type::Int);
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let record_type = Type::Signal(Box::new(Type::Record(fields)));
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checker.env.insert("rec".to_string(), record_type);
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let expr = Expr::DotAccess(
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Box::new(Expr::Ident("rec".to_string())),
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"x".to_string(),
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);
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let ty = checker.infer_expr(&expr);
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assert_eq!(ty, Type::Int);
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assert!(!checker.has_errors(), "Errors: {}", checker.display_errors());
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}
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#[test]
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fn test_if_else_branch_unification() {
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let mut checker = TypeChecker::new();
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let program = make_program(vec![
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Declaration::Let(LetDecl {
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name: "flag".to_string(),
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type_annotation: None,
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value: Expr::BoolLit(true),
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span: span(),
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}),
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Declaration::Let(LetDecl {
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name: "result".to_string(),
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type_annotation: None,
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value: Expr::If(
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Box::new(Expr::Ident("flag".to_string())),
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Box::new(Expr::IntLit(1)),
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Box::new(Expr::IntLit(2)),
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),
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span: span(),
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}),
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]);
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checker.check_program(&program);
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assert!(!checker.has_errors(), "Errors: {}", checker.display_errors());
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}
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#[test]
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fn test_for_in_binds_item_type() {
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let mut checker = TypeChecker::new();
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let program = make_program(vec![
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Declaration::Let(LetDecl {
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name: "nums".to_string(),
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type_annotation: None,
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value: Expr::List(vec![
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Expr::IntLit(1),
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Expr::IntLit(2),
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Expr::IntLit(3),
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]),
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span: span(),
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}),
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Declaration::Let(LetDecl {
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name: "total".to_string(),
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type_annotation: None,
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value: Expr::ForIn {
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item: "n".to_string(),
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index: None,
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iter: Box::new(Expr::Ident("nums".to_string())),
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body: Box::new(Expr::Ident("n".to_string())),
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},
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span: span(),
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}),
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]);
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checker.check_program(&program);
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assert!(!checker.has_errors(), "Errors: {}", checker.display_errors());
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// The iteration variable 'n' should have been bound as Int
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let n_ty = checker.type_env().get("n").unwrap();
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assert_eq!(*n_ty, Type::Int);
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}
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#[test]
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fn test_assign_type_compatibility() {
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let mut checker = TypeChecker::new();
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let program = make_program(vec![
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Declaration::Let(LetDecl {
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name: "count".to_string(),
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type_annotation: None,
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value: Expr::IntLit(0),
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span: span(),
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}),
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]);
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checker.check_program(&program);
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assert!(!checker.has_errors());
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// Assigning an Int to a Signal<Int> should be fine
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let assign_expr = Expr::Assign(
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Box::new(Expr::Ident("count".to_string())),
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ds_parser::AssignOp::Set,
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Box::new(Expr::IntLit(5)),
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);
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let ty = checker.infer_expr(&assign_expr);
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assert_eq!(ty, Type::Unit);
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assert!(!checker.has_errors(), "Errors: {}", checker.display_errors());
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}
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#[test]
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fn test_unify_fn_arg_types() {
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let mut checker = TypeChecker::new();
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// Register a function: add(Int, Int) -> Int
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let fn_type = Type::Fn {
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params: vec![Type::Int, Type::Int],
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ret: Box::new(Type::Int),
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effects: vec![EffectType::Pure],
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};
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checker.env.insert("add".to_string(), fn_type);
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// Call with correct types should work
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let call_expr = Expr::Call("add".to_string(), vec![
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Expr::IntLit(1),
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Expr::IntLit(2),
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]);
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let ty = checker.infer_expr(&call_expr);
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assert_eq!(ty, Type::Int);
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assert!(!checker.has_errors(), "Errors: {}", checker.display_errors());
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}
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}
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