check if/else expressions #63

Merged

jacksonopp merged 4 commits from us54/check-if-else into main

2026-09-16 18:35:40 +00:00

jacksonopp commented

2026-09-16 18:22:25 +00:00

Owner

Closes #54.

Type-checks Expr::If: condition must be Bool (reports InvalidConditional otherwise), both branches must agree on their result type when else is present (reports the new MismatchedElse diagnostic otherwise, resolving to the then branch's type), and the expression resolves to Unit when else is absent, mirroring Expr::Block's trailing-expr-less case.

Test plan

cargo test -p twill-check (new unit tests for matching branches, no-else, non-Bool cond, mismatched branches, and a failing else branch not double-reporting)

Closes #54. Type-checks `Expr::If`: condition must be `Bool` (reports `InvalidConditional` otherwise), both branches must agree on their result type when `else` is present (reports the new `MismatchedElse` diagnostic otherwise, resolving to the `then` branch's type), and the expression resolves to `Unit` when `else` is absent, mirroring `Expr::Block`'s trailing-expr-less case. ## Test plan - [x] `cargo test -p twill-check` (new unit tests for matching branches, no-else, non-`Bool` cond, mismatched branches, and a failing else branch not double-reporting)

jacksonopp added 2 commits

2026-09-16 18:22:25 +00:00