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Source status: no status is stated in the source document, so none is assigned here. Do not treat this page as a finalized specification. The normative rules are in the Technical Specification.

Function Design

Every function must explicitly declare its contract.

Required Declarations

  1. Inputs: What information the function accepts, including data types and constraints.
  2. Outputs: What the function can return.
  3. Preconditions: What must be true before execution.
  4. Postconditions: What must be true after successful execution.
  5. Side Effects: What external state the function is allowed to modify.
  6. Failure Conditions: What can cause the function to fail and how those failures are reported.

Function Rules

  • Functions cannot silently modify undeclared external state.
  • All possible outcomes must be accounted for.
  • Preconditions must be checked or established by the caller.
  • Successful execution must satisfy the declared postconditions.
  • Guarantees must be distinguishable from assumptions.
  • The compiler must reject functions with incomplete required declarations.

Design Goal

An AI agent should be able to understand exactly what a function expects, what it is allowed to do, and what it promises to accomplish before implementing it.

Source and authority

This page migrates FUNCTIONS.md in full. It is an explanatory / implementation document, not the normative specification. Where it simplifies a rule, the Technical Specification governs. The original file is preserved in source-original/LANG/.