Why does TypeScript not infer types for some piped functions?
This issue is still outstanding, but for now I wanted to post a workaround that I've come up with because I found it very useful in my experience.
Create a utility function like this:
export const call = <A, B>(f: (x: A) => B) => f;(the same function as in the question, an identity function that takes a unary function as argument), and then whenever you run into trouble with an arrow function in your pipe, try enclosing it with this utility function. Counterintuitively, TS can't handle this:
const a = pipe(1, x => x + 1, call(x => x + 1));but it can handle this:
const c = pipe(1, call(x => x + 1), call(x => x + 1));(no idea why). Later when the issue is fixed (go ahead an upvote it: https://github.com/Microsoft/TypeScript/issues/22081), you'll be able to easily find all references to call and remove them.