Type system and inference rules

Goals

• Deterministic typing for CLIF lowering.
• Minimal implicit behavior; prefer explicit casts.

Type inference strategy

• Constraint-based inference (HM-lite) for locals and non-generic expressions.
• Generics resolved during type checking using declared bounds.

Literal typing (decision)

• Integer literals default to i32.
• Float literals default to f64.
• Boolean literals map to bool.
• String literals map to {ptr, len} at runtime, string in HIR.

Numeric coercions

• Implicit widening allowed only for:
  • i32 -> i64
  • f32 -> f64
• All other conversions require explicit cast.
• Mixed int/float expressions require explicit cast.

Type checking phases

1. Collect declarations.
2. Resolve names (module + local scopes).
3. Solve type constraints.
4. Insert explicit Cast nodes.

Error reporting

• Unknown type: TypeNotFound.
• Incompatible types: TypeMismatch.
• Ambiguous inference: TypeInferenceAmbiguous.