rklaehn/adt-ts

Type-safe algebraic data types and pattern matching in typescript 2.8

adt-ts's Issues

Tupled constructors

This a great library for ADTs in TypeScript, actually it's the only one I found that actually works well even for recursive types. Right now I'm using it like this:

export type Term = FromCases<{
  Var: { tag: 'Var', index: number };
  Global: { name: Name },
  Abs: { body: Term },
  App: { left: Term, right: Term },
  Pair: { fst: Term, snd: Term },
  Proj: { proj: 'fst' | 'snd', term: Term },
  Let: { val: Term, body: Term },
}>;
export const TermC = Constructor<Term>();

export const Var = (index: number): Term => TermC.Var({ index });
export const Global = (name: Name): Term => TermC.Global({ name });
export const App = (left: Term, right: Term): Term => TermC.App({ left, right });
export const Abs = (body: Term): Term => TermC.Abs({ body });
export const Pair = (fst: Term, snd: Term): Term => TermC.Pair({ fst, snd });
export const Proj = (proj: 'fst' | 'snd', term: Term): Term => TermC.Proj({ proj, term });
export const Let = (val: Term, body: Term): Term => TermC.Let({ val, body });

The only annoyance I have is that I have to write out the constructors explicitly because I'd like the arguments to not be in an object. Do you think it's technically possible in TypeScript to automatically generate the "tupled" constructors as well?

Side note: the use of Proxy seems to slow things down a lot, if I manually write constructors I get a 2x speedup compared to using the constructors from Constructor. Maybe it's possible to write a version of Constructor where the user has to manually provide that tags so that Proxy is not needed. Maybe something like:

export const ConstructorFast = <T extends Tagged>(o: { [K in T['type']]: {} }): Constructor<T> => {
  const n: any = {};
  for (const k in o) n[k] = (args: any) => ({ type: k, ...args });
  return n;
};