iter 22b.3.4: fix — quality-review (zero-arg test, drop what-comments + param-name pin)

crates/ail/tests/typeclass_22b3.rs

@@ -304,6 +304,65 @@ fn synthesise_mono_fn_falls_back_to_class_default() {
 
     let f = synthesise_mono_fn(&target, &class_def, &instance).expect("synth");
     assert_eq!(f.name, "hello#Int");
-    assert_eq!(f.params, vec!["_x".to_string()]);
+    assert_eq!(
+        f.params.len(),
+        1,
+        "default-fallback Lam carries 1 param: {:?}",
+        f.params
+    );
     assert!(matches!(&f.body, Term::Lit { .. }), "body = {:?}", f.body);
 }
+
+/// Zero-arg method (no positional params): body is used verbatim
+/// without Lam-unwrapping. Class `Foo a where bar : Int` (note: no
+/// arrow — the method is a constant), instance `Foo Int where bar
+/// = 7`. synthesise_mono_fn must produce
+/// `FnDef { name: "bar#Int", ty: Int, params: [], body: Lit 7 }`.
+#[test]
+fn synthesise_mono_fn_zero_arg_method_uses_body_verbatim() {
+    use ailang_check::mono::{synthesise_mono_fn, MonoTarget};
+    use ailang_core::ast::{ClassDef, ClassMethod, InstanceDef, InstanceMethod, Literal, Term};
+
+    let class_def = ClassDef {
+        name: "Foo".into(),
+        param: "a".into(),
+        superclass: None,
+        methods: vec![ClassMethod {
+            name: "bar".into(),
+            // Zero-arg method: ty is the value type directly, not a Type::Fn.
+            ty: Type::int(),
+            default: None,
+        }],
+        doc: None,
+    };
+    let instance = InstanceDef {
+        class: "Foo".into(),
+        type_: Type::int(),
+        methods: vec![InstanceMethod {
+            name: "bar".into(),
+            // Body is a value directly — no Lam wrapper.
+            body: Term::Lit {
+                lit: Literal::Int { value: 7 },
+            },
+        }],
+        doc: None,
+    };
+    let target = MonoTarget {
+        class: "Foo".into(),
+        method: "bar".into(),
+        type_: Type::int(),
+        defining_module: "m".into(),
+    };
+
+    let f = synthesise_mono_fn(&target, &class_def, &instance).expect("synth");
+    assert_eq!(f.name, "bar#Int");
+    assert!(
+        f.params.is_empty(),
+        "zero-arg method must produce empty params"
+    );
+    assert!(
+        matches!(&f.body, Term::Lit { lit: Literal::Int { value: 7 } }),
+        "body must be the verbatim Lit, got {:?}",
+        f.body
+    );
+}

crates/ailang-check/src/mono.rs

@@ -359,7 +359,6 @@ pub fn synthesise_mono_fn(
         Type::Fn { params, .. } if !params.is_empty()
     );
     let (params, body): (Vec<String>, Term) = if method_has_params {
-        // Method has positional params — body must be a Lam.
         match body_term {
             Term::Lam { params, body, .. } => (params, *body),
             other => {
@@ -371,7 +370,6 @@ pub fn synthesise_mono_fn(
             }
         }
     } else {
-        // Zero-arg method — body is the value directly.
         (Vec::new(), body_term)
     };