floats iter 3.1: widen +/-/*/// and !=/</<=/>/>= to polymorphic forall a

crates/ailang-codegen/src/synth.rs

@@ -59,6 +59,39 @@ pub(crate) fn fn_sig_from_type(t: &Type) -> Option<FnSig> {
 /// `synth_arg_type` for arg-type inference at polymorphic call sites.
 /// Mirrors what the typechecker installs in its env via `builtins`.
 pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
+    // Iter 22-floats.3: same widening as `crates/ailang-check/src/
+    // builtins.rs` — `+`/`-`/`*`/`/` and `!=`/`<`/`<=`/`>`/`>=` are
+    // polymorphic. `%` stays monomorphic-Int. Codegen lowering for
+    // these ops still goes through `builtin_binop` (Int-only) in
+    // iter 3; iter 4 converts that to type-dispatched.
+    let poly_a_a_to_a = || Type::Forall {
+        vars: vec!["a".into()],
+        constraints: vec![],
+        body: Box::new(Type::Fn {
+            params: vec![
+                Type::Var { name: "a".into() },
+                Type::Var { name: "a".into() },
+            ],
+            ret: Box::new(Type::Var { name: "a".into() }),
+            effects: vec![],
+            param_modes: vec![],
+            ret_mode: ParamMode::Implicit,
+        }),
+    };
+    let poly_a_a_to_bool = || Type::Forall {
+        vars: vec!["a".into()],
+        constraints: vec![],
+        body: Box::new(Type::Fn {
+            params: vec![
+                Type::Var { name: "a".into() },
+                Type::Var { name: "a".into() },
+            ],
+            ret: Box::new(Type::bool_()),
+            effects: vec![],
+            param_modes: vec![],
+            ret_mode: ParamMode::Implicit,
+        }),
+    };
     let int_int_int = || Type::Fn {
         params: vec![Type::int(), Type::int()],
         ret: Box::new(Type::int()),
@@ -66,16 +99,10 @@ pub(crate) fn builtin_ail_type(name: &str) -> Option<Type> {
         param_modes: vec![],
         ret_mode: ParamMode::Implicit,
     };
-    let int_int_bool = || Type::Fn {
-        params: vec![Type::int(), Type::int()],
-        ret: Box::new(Type::bool_()),
-        effects: vec![],
-        param_modes: vec![],
-        ret_mode: ParamMode::Implicit,
-    };
     Some(match name {
-        "+" | "-" | "*" | "/" | "%" => int_int_int(),
-        "!=" | "<" | "<=" | ">" | ">=" => int_int_bool(),
+        "+" | "-" | "*" | "/" => poly_a_a_to_a(),
+        "%" => int_int_int(),
+        "!=" | "<" | "<=" | ">" | ">=" => poly_a_a_to_bool(),
         // Iter 16e: `==` is polymorphic — `forall a. (a, a) -> Bool`.
         // The mono pipeline asks `synth_arg_type` for the actual arg
         // types at the call site; `lower_app` then dispatches to the