v6 Semantics: type checking

This stage enforces static types before code generation.

Core checks

• every expression has a type
• assignments are type-compatible
• function calls match param types
• returns match declared return type

Inference rules

• let x = 1; infers number
• let xs = []; is an error (needs annotation)

Type errors (examples)

• let x: number = "hi"; => type mismatch
• true + 1 => invalid operands
• fn f(a: number) -> number { return "x"; } => return type mismatch

Collections

• arrays are homogenous
• maps have consistent key/value types
• map keys must be number/bool/string