Discussion on "Practical Guide to Fp-ts P4: Arrays, Semigroups, Monoids" | Hashnode

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Carsten Leue

Hi Ryan, I am really enjoying your series of articles about fp-ts. The pragmatic approach and real life usecases help a lot.

I'd like to give the following feedback and would be interested to see your views on that:

in your examples across the series you are importing from fp-ts/lib/, but that one is the commonjs version. Wouldn't it be more flexible to import from fp-ts instead and rely on the main and module entry point in the package.json for fp-ts to locate the best version, e.g.

import * as A from 'fp-ts/Array'
import { pipe } from 'fp-ts/function'

...

in the pipe examples you chose a version of the operators that accepts the array as a parameter. This looks a bit asymmetric to the subsequent operators that use the raw transformer function. I wonder why you chose this style instead of e.g.

import * as A from 'fp-ts/Array'
import { pipe } from 'fp-ts/function'

const foo = [1, 2, 3, 4, 5]

const sum = pipe(
  foo,
  A.map((x) => x - 1),
  A.filter((x) => x % 2 === 0),
  A.reduce(0, (prev, next) => prev + next),
)
console.log(sum) // 6

-

Ryan Lee

I believe if you use /lib it will treeshake where as if you use fp-ts directly it will not. Sorry for the extremely late reply. I never got a notif for this!

thanks for answering. I have done some investigation since and also addressed the same in fp-ts issues 1606 because Giulio Canti's examples also imported from /lib. According to my own experiments and the comments on the issue above, the tree shakable import is without /lib, because /lib references the CJS version of the code.