Function countBy

scripts/fungrim/compile-rules.ts:1602–1606

(xs: ReadonlyArray<T>, key: (x: T) => string)

  // then (e.g. the Tier-2 special-function kernels) are pruned here against
  // a live stock engine, so the artifact stays in sync with the engine it
  // ships with. (The loader also skips already-defined names at load time —
  // this keeps the artifact, not just the load, accurate.)
  const pruned: CompileResult['declarations'] = {};
  const builtinProbe = new ComputeEngine();
  const usedShells = new Set<string>();
  for (const r of rules) {
    collectSymbols(r.match, usedShells);
    collectSymbols(r.replace, usedShells);