Purity

Jazz separates known effectful calls from ordinary functions. It currently tracks that boundary through names: a name ending in ! is impure, while every other binding is pure by default.

The compiler enforces three rules:

• a pure binding body cannot directly call a known impure callee;
• an impure binding may call pure or impure callees; and
• top-level expression statements may call impure names so programs can perform entry-point effects.

The host-I/O functions in the IO module follow this naming contract.

Partial: this is direct-call analysis, not an effect type system. It does not prove the purity of unknown higher-order callables, propagate effects polymorphically, analyze a cross-module call graph, or enforce purity at runtime. Those areas remain planned.