Lykn

The Three Compilation Phases

After macro expansion, the surface compiler runs three phases.

Phase 1: Collection

Build the type registry and function signatures.

• Scan for type definitions: register constructors, field names, field types, blessed type flags (Option, Result)
• Scan for func signatures: register arities, type keywords, multi-clause dispatch signatures
• Load prelude: Option and Result from lykn/core, auto-imported into every module

Phase 2: Analysis

Check correctness using the collected information.

Exhaustiveness checking (DD-21): For every match expression, verify all variants are covered. Uses Maranget’s algorithm. Guards make clauses partial — they don’t count toward coverage.

Overlap detection: For every multi-clause func, verify no two clauses accept the same argument types. Same algorithm, different consumer.

Scope tracking: Track every binding introduced by bind, func, fn, destructuring, for-of, try/catch. Detect unused bindings (warnings) and undefined references (errors).

Type inference from patterns: Constructor patterns infer the matched type. Mixed constructors from different types are a compile error.

Phase 3: Emission

Transform the analyzed surface AST into kernel forms.

• func → function with type checks, contracts, dispatch chain
• bind → const with type check if annotated (DD-24)
• fn → => with type checks
• type → constructor functions with field validation
• match → nested if chains (IIFE in value position)
• cell → { value: x }, threading macros → nested calls or IIFEs
• --strip-assertions → type checks and contracts removed

The emitter produces kernel forms that feed into the JS kernel compiler (Ch 32) or the Rust codegen. The full pipeline from surface source to JavaScript is complete.