The Monad Fear: javascript response

the_monad_fear.js

// https://e.xtendo.org/monad#55

['10', '10', '10'].map(parseInt);
//> [10, NaN, 2]
// parseInt('10', 0, [...]) === 10 // base 0 is falsey, thus default (?) guessing
// parseInt('10', 1, [...]) === NaN // base 1 does not compute
// parseInt('10', 2, [...]) === 2 // base 2
// third parameter ignored; second parameter passed as index from map to functor

// higher-order functor to the rescue!
const onlyFirst = fun => single => fun(single);
['10', '10', '10'].map(onlyFirst(parseInt));
//> [10, 10, 10]

// As a higher-order functor, `onlyFirst` takes and returns a functor, and is a functor itself
// While the index-as-base problem is solved, `parseInt` can demonstrate complex behavior
// Simple example of hexadecimal prefix `0x`
// `parseFloat` doesn't recognize; reads the first digit character up to the first non-digit character, thus interpreting the prefix as `0`
// By using the higher-order functor, compare/contrast comes easily
const withHexString = ['10', '10', '10', '0x10'];
[parseInt, parseFloat].map(onlyFirst).map(fn => withHexString.map(fn));
//> [[10, 10, 10, 16], [10, 10, 10, 0]]

// Copy and paste gist contents into your console! (Chrome/Firefox macOS Sierra tested)

@hartbeatnt - equally as valid, but not a higher order Functor, just a handy lambda. onlySingle can work with functions other than parseInt with minimal repetition. DRY vs abstraction overkill.

Honestly, I'd more likely write your solution than the generalized solution in practice, but as a response to Haskell programmers, it's nice to show off the FP capabilities of JS.