@typesugar/preprocessor

Lexical preprocessor for typesugar syntax extensions.

This package provides a lexical preprocessing layer that transforms custom syntax (F<_> HKT, |> pipeline, :: cons) into valid TypeScript before the macro transformer runs.

Installation

npm install @typesugar/preprocessor

Usage

import { preprocess } from "@typesugar/preprocessor";

const source = `
  interface Functor<F<_>> {
    map: <A, B>(fa: F<A>, f: (a: A) => B) => F<B>;
  }

  const result = x |> f |> g;
`;

const { code, changed, sourceMap } = preprocess(source);
// code is now valid TypeScript with F<A> rewritten to $<F, A>
// and |> rewritten to __binop__ calls

Syntax Extensions

HKT Syntax (F<_>)

Higher-kinded type parameters are rewritten using the $<F, A> encoding:

// Input
interface Functor<F<_>> {
  map: <A, B>(fa: F<A>, f: (a: A) => B) => F<B>;
}

// Output
interface Functor<F> {
  map: <A, B>(fa: $<F, A>, f: (a: A) => B) => $<F, B>;
}

Pipeline Operator (|>)

The pipeline operator is rewritten to __binop__ calls for resolution:

// Input
const result = x |> f |> g;

// Output
const result = __binop__("|>", __binop__("|>", x, f), g);

Cons Operator (::)

List construction syntax for functional data structures:

// Input
const list = 1 :: 2 :: 3 :: nil;

// Output
const list = __binop__("::", 1, __binop__("::", 2, __binop__("::", 3, nil)));

API

preprocess(source, options?)

Preprocess source code, applying all syntax extensions.

• source: The TypeScript source code
• options.fileName: File name for JSX detection (.tsx files get JSX-aware tokenization)
• options.sourceMap: Whether to generate source maps (default: true)

Returns { code, changed, sourceMap }.

tokenize(source, options?)

Tokenize source code into a stream of tokens.

TokenStream

A stream wrapper for efficient token consumption with lookahead.

License

MIT