iter 22b.2.1: add Constraint struct, Type::Forall.constraints

crates/ailang-check/src/builtins.rs

@@ -79,6 +79,7 @@ pub fn install(env: &mut crate::Env) {
         "==".into(),
         Type::Forall {
             vars: vec!["a".into()],
+            constraints: vec![],
             body: Box::new(Type::Fn {
                 params: vec![
                     Type::Var { name: "a".into() },
@@ -112,6 +113,7 @@ pub fn install(env: &mut crate::Env) {
         "__unreachable__".into(),
         Type::Forall {
             vars: vec!["a".into()],
+            constraints: vec![],
             body: Box::new(Type::Var { name: "a".into() }),
         },
     );

crates/ailang-check/src/lib.rs

@@ -96,8 +96,9 @@ impl Subst {
                 param_modes: vec![],
                 ret_mode: ParamMode::Implicit,
             },
-            Type::Forall { vars, body } => Type::Forall {
+            Type::Forall { vars, constraints, body } => Type::Forall {
                 vars: vars.clone(),
+                constraints: constraints.clone(),
                 body: Box::new(self.apply(body)),
             },
         }
@@ -136,7 +137,7 @@ fn substitute_rigids(t: &Type, mapping: &BTreeMap<String, Type>) -> Type {
             param_modes: vec![],
             ret_mode: ParamMode::Implicit,
         },
-        Type::Forall { vars, body } => {
+        Type::Forall { vars, constraints, body } => {
             // Inner forall shadows: only substitute vars not re-bound here.
             let inner: BTreeMap<String, Type> = mapping
                 .iter()
@@ -145,6 +146,7 @@ fn substitute_rigids(t: &Type, mapping: &BTreeMap<String, Type>) -> Type {
                 .collect();
             Type::Forall {
                 vars: vars.clone(),
+                constraints: constraints.clone(),
                 body: Box::new(substitute_rigids(body, &inner)),
             }
         }
@@ -1082,7 +1084,7 @@ fn check_fn(f: &FnDef, env: &Env) -> Result<()> {
     // with themselves. An empty `vars` list (vacuously polymorphic)
     // gets normalised to a non-polymorphic body.
     let (rigids, inner_ty): (Vec<String>, Type) = match &f.ty {
-        Type::Forall { vars, body } => (vars.clone(), (**body).clone()),
+        Type::Forall { vars, constraints: _, body } => (vars.clone(), (**body).clone()),
         other => (vec![], other.clone()),
     };
 
@@ -1337,7 +1339,7 @@ pub(crate) fn synth(
                 Type::Fn { params, ret, effects: fx, .. } => {
                     (params.clone(), (**ret).clone(), fx.clone())
                 }
-                Type::Forall { vars, body } => {
+                Type::Forall { vars, constraints: _, body } => {
                     // Defensive — Var should already have instantiated.
                     let (_, body) = instantiate(vars, body, counter);
                     match &body {
@@ -1797,7 +1799,7 @@ pub(crate) fn synth(
 /// If `t` is a `Forall`, instantiate it with fresh metavars; otherwise
 /// pass through unchanged. Used at every var-resolution site.
 fn maybe_instantiate(t: Type, counter: &mut u32) -> Type {
-    if let Type::Forall { vars, body } = &t {
+    if let Type::Forall { vars, constraints: _, body } = &t {
         let (_, inst) = instantiate(vars, body, counter);
         inst
     } else {
@@ -1845,8 +1847,9 @@ fn qualify_local_types(t: &Type, owner_module: &str, local_types: &IndexMap<Stri
             param_modes: vec![],
             ret_mode: ParamMode::Implicit,
         },
-        Type::Forall { vars, body } => Type::Forall {
+        Type::Forall { vars, constraints, body } => Type::Forall {
             vars: vars.clone(),
+            constraints: constraints.clone(),
             body: Box::new(qualify_local_types(body, owner_module, local_types)),
         },
         Type::Var { .. } => t.clone(),
@@ -2380,6 +2383,7 @@ mod tests {
                 "id",
                 Type::Forall {
                     vars: vec!["a".into()],
+                    constraints: vec![],
                     body: Box::new(Type::Fn {
                         params: vec![Type::Var { name: "a".into() }],
                         ret: Box::new(Type::Var { name: "a".into() }),
@@ -2405,6 +2409,7 @@ mod tests {
             "id",
             Type::Forall {
                 vars: vec!["a".into()],
+                constraints: vec![],
                 body: Box::new(Type::Fn {
                     params: vec![Type::Var { name: "a".into() }],
                     ret: Box::new(Type::Var { name: "a".into() }),
@@ -2468,6 +2473,7 @@ mod tests {
             "id",
             Type::Forall {
                 vars: vec!["a".into()],
+                constraints: vec![],
                 body: Box::new(Type::Fn {
                     params: vec![Type::Var { name: "a".into() }],
                     ret: Box::new(Type::Var { name: "a".into() }),
@@ -2516,6 +2522,7 @@ mod tests {
             "apply",
             Type::Forall {
                 vars: vec!["a".into(), "b".into()],
+                constraints: vec![],
                 body: Box::new(Type::Fn {
                     params: vec![
                         Type::Fn {
@@ -2649,6 +2656,7 @@ mod tests {
             name: "unbox".into(),
             ty: Type::Forall {
                 vars: vec!["a".into()],
+                constraints: vec![],
                 body: Box::new(Type::Fn {
                     params: vec![Type::Con {
                         name: "Box".into(),
@@ -3708,6 +3716,7 @@ mod tests {
                 "outer",
                 Type::Forall {
                     vars: vec!["a".into()],
+                    constraints: vec![],
                     body: Box::new(Type::Fn {
                         params: vec![Type::Var { name: "a".into() }],
                         ret: Box::new(Type::Var { name: "a".into() }),
@@ -3788,7 +3797,7 @@ mod tests {
         // Original LetRec params: [Int]; captures (BTreeSet order):
         // x: a then z: Int (alphabetical). Ret: a.
         match &synth.ty {
-            Type::Forall { vars, body } => {
+            Type::Forall { vars, constraints: _, body } => {
                 assert_eq!(
                     vars,
                     &vec!["a".to_string()],

crates/ailang-check/src/lift.rs

@@ -558,6 +558,7 @@ impl<'a> Lifter<'a> {
                 } else {
                     Type::Forall {
                         vars: self.current_def_forall_vars.clone(),
+                        constraints: vec![],
                         body: Box::new(inner_augmented_ty),
                     }
                 };
@@ -867,7 +868,7 @@ fn substitute_rigids_local(t: &Type, mapping: &BTreeMap<String, Type>) -> Type {
             param_modes: vec![],
             ret_mode: ParamMode::Implicit,
         },
-        Type::Forall { vars, body } => {
+        Type::Forall { vars, constraints, body } => {
             let inner: BTreeMap<String, Type> = mapping
                 .iter()
                 .filter(|(k, _)| !vars.contains(k))
@@ -875,6 +876,7 @@ fn substitute_rigids_local(t: &Type, mapping: &BTreeMap<String, Type>) -> Type {
                 .collect();
             Type::Forall {
                 vars: vars.clone(),
+                constraints: constraints.clone(),
                 body: Box::new(substitute_rigids_local(body, &inner)),
             }
         }