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Functional design: combinators

Giulio Canti on February 19, 2019

In this article the term "combinator" refers to the combinator pattern A style of organizing libraries centered around the idea of combining thin...

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Gabriel Lebec • Apr 2 '19

I recently wrote about the combinator pattern in my article on property testing via JSVerify. I blinked just now at reading the phrase "combinatorial explosion" which we both used in our articles – but it turns out you wrote it first (Feb. vs Mar.)! Um, great minds think alike?

Anyway, combinators to me represent almost the entire point of FP – composition. The ability to connect pieces of code together seamlessly, building up complexity without getting lost in the wiring. This article has some nice examples.

I recently became aware of FP-TS from a tweet; it looks good! Might be the lever that finally pushes me into adopting TS itself, as FP in JS works but I miss the typing of e.g. Haskell. Enjoying your article series, thanks for posting it.

Dan Minshew • May 28 '19

Hey you might enjoy exploring how this term is used in a variety of contexts, it's quite useful!

google.com/search?q=combinatorial+...

Fabien Bourgeois • May 30 '19

About you search on functional JS typing, you may already heard of Sanctuary-def. You loose static analysis but gain runtime (optional) type system. It supports Hindley-Milner like type signature.

Daniel Rodríguez Rivero • Feb 25 '19

This seems to be a nice post, but typescript makes it so hard to read...

SHND • Apr 23

Seems one parentheses extra here?

export function replicateIO(n: number, mv: IO<void>): IO<void> {
  return concatAll(getMonoid(monoidVoid))(replicate(n, mv))
}

export function replicateIO(n: number, mv: IO<void>): IO<void> {
  return concatAll(getMonoid(monoidVoid)(replicate(n, mv))
}

naorzr • Feb 21 '21

Great article,

Small correction, I believe "contramap" is logically wrong.
Just because we have a function from B->A doesn't necessarily means that applying these functions and then using equal is the same as applying equal to the instances of B.
it lacks assumptions for this to be true.
for example:
lets say B is simply numbers, and A are simply strings,
the function that converts these operate by the following logic, all positive numbers transformed to the latter 'p', and all the negatives to the latter 'n',
so,
f(2) === f(3)
but 2!==3.