Wordle in FP-TS

wordle-fp-ts.ts

import { ap, of, intersection } from 'fp-ts/Array'
import { Eq as StringEq } from 'fp-ts/string'
import { pipe } from 'fp-ts/function'

// Our word bank, shortened for brevity.
const wordBank = ['wince', 'hinge', 'movie', 'arbor' /** More */]

// Here is the function I need to write that can evaluate individual solutions. Note I have
// to write it in a curried form.
const word = (a: string) => (b: string) => (c: string) => `${a}i${b}${c}e`

// Here I am lifting "word" into the Array's applicative context, and applying an array functor (the letters)
// to each of its arguments using pipe. FP-TS can fully and correctly type this.
// Given how the Array applicative works, this function will generate all permutations of the letters passed in
// against the template defined in "word".
const allWords = (letters: string[]) => pipe(of(word), ap(letters), ap(letters), ap(letters))

// This function composes "allWords" and compares to a full word bank. The "intersection" function
// from FP-TS requires us to specify how to compare two things from each list, that's why I am passing
// in a function defined by FP-TS itself to compare two strings.
const allValidWords = (letters: string[]) => pipe(allWords(letters), intersection(StringEq)(wordBank))

// Take it for a spin. For above word bank, will return:  ['wince', 'hinge']
allValidWords(['w', 't', 'y', 'g', 'h', 'j', 'k', 'c', 'n'])

Compare to the Ramda version here.

This solution is only one line longer than the Ramda solution, but much stronger typed! FP-TS doesn't include a point-free function for "lifting" a function like Ramda does due to Typescript typing issues, but hopefully line 16 isn't too difficult to parse.

I will write another example using a different applicative where the equivalent lifting line will essentially look the same.