Lambdas and Closures

Scope

This document is the canonical source for lambda and closure semantics in v0.1.

17.1 Lambda forms

Lambdas use => and are first-class callable values.

Examples:

let isEven = x => x % 2 == 0;
let add = (i32 x, i32 y) => x + y;
let f = x => {
    IO.Println(x.ToString());
    return x;
};

17.2 Type model

Function types use arrow syntax:

(T1, T2) -> TOut

Lambdas are assignable to compatible function types.

17.3 Inference rules

• Lambda parameter types MAY be inferred from an expected function type.
• If no expected function type exists, parameter types MUST be explicit.
• Lambda return type is inferred from lambda body when the expected function type is known.

17.4 Capture and closure rules

• Non-capturing lambdas lower as plain callable values.
• Capturing lambdas are supported under non-escape constraints.
• Captured environments MUST NOT escape safe scope in v0.1.

17.5 Interaction with query/event features

• Query pipelines MAY accept lambda callables (Where, Select style operators).
• Event handlers MAY be lambda values if signature-compatible (for event Name(...) / event{N} Name(...) fields subscribed via +=).
• Query/event sections should reference this document for closure semantics.

17.6 Diagnostics (required)

Compilation MUST diagnose:

• missing parameter types when no expected function type exists,
• incompatible lambda signature at assignment/call site,
• unsupported escaping captured environments.

17.7 Cross references

• Syntax examples: docs/spec/lexical-and-syntax.md
• Type grammar: docs/spec/types.md
• Inference core: docs/spec/type-inference.md
• Query contracts: docs/standard-library/Query/Contracts.md
• Event semantics: docs/spec/events.md