hkts

Higher kinded types for Deno. As an avid user of fp-ts I wanted to have a similarly full featured environment in Deno. Unfortunately, the fp-ts port to Deno is clunky to use with other functional libraries like @nll/datum, io-ts, and monocle-ts. While I could have ported fp-ts directly, I’ve come to like the exploratory work done by pelotom in the original hkts. Thus, I’ve decided to port the functionality of fp-ts, io-ts, and monocle-ts to Deno using the HKT substitution developed by pelotom.

This library is primarily an exercise, but I intend to maintain 100% test coverage. Instead of breaking out the clones of io-ts, monocle-ts, and datum into other Deno modules they will all be landed here. There will be no barrel exports as importing in Deno is much cleaner without them. Contributions are welcome.

Installation

This library is meant to be used with Deno, thus it follows the Deno imports syntax.

import * as O from "https://deno.land/x/hkts/option.ts";
import { pipe } from "https://deno.land/x/hkts/fns.ts";

const result = pipe(
    O.some(1),
    O.map(n => n + 1),
    O.chain(n => n % 2 === 0 ? O.none, O.some(n))
);
// result = O.none.

Conventions

This library focuses first on implementing static-land type classes for a given Algebraic Data Type (ie. Either or Option) first. These type class instances are then exported from the ADT’s namespace (eg. import { Monad } from 'https://deno.land/x/hkts/option.ts'). With the exception of instance constructors (ie. getShow or getSemigroup) other ADT functions should all be pipeable. For functions that derive from type class modules, like chain or map, there are helpers in type-classes.ts that will generate the pipeable versions for you.

For good examples of the above conventions look at the either.ts or option.ts.

Documentation

For the foreseeable future this library will not focus on documentation. Questions are welcome via github issues but I can’t guaruntee speedy responses. Once a decent collection of ADTs and other utilities are ported and all the pre-1.0.0 todo items in TODO.md are complete I’ll shift to documentation. Even then it’s likely that I’ll auto-generate the raw docs from exported function and statement types and will devote any time to building an example library that doubles as extra tests.