62 lines
1.5 KiB
TypeScript
62 lines
1.5 KiB
TypeScript
type Func<T extends any[], R> = (...a: T) => R
|
|
|
|
/**
|
|
* Composes single-argument functions from right to left. The rightmost
|
|
* function can take multiple arguments as it provides the signature for the
|
|
* resulting composite function.
|
|
*
|
|
* @param funcs The functions to compose.
|
|
* @returns A function obtained by composing the argument functions from right
|
|
* to left. For example, `compose(f, g, h)` is identical to doing
|
|
* `(...args) => f(g(h(...args)))`.
|
|
*/
|
|
export default function compose(): <R>(a: R) => R
|
|
|
|
export default function compose<F extends Function>(f: F): F
|
|
|
|
/* two functions */
|
|
export default function compose<A, T extends any[], R>(
|
|
f1: (a: A) => R,
|
|
f2: Func<T, A>
|
|
): Func<T, R>
|
|
|
|
/* three functions */
|
|
export default function compose<A, B, T extends any[], R>(
|
|
f1: (b: B) => R,
|
|
f2: (a: A) => B,
|
|
f3: Func<T, A>
|
|
): Func<T, R>
|
|
|
|
/* four functions */
|
|
export default function compose<A, B, C, T extends any[], R>(
|
|
f1: (c: C) => R,
|
|
f2: (b: B) => C,
|
|
f3: (a: A) => B,
|
|
f4: Func<T, A>
|
|
): Func<T, R>
|
|
|
|
/* rest */
|
|
export default function compose<R>(
|
|
f1: (a: any) => R,
|
|
...funcs: Function[]
|
|
): (...args: any[]) => R
|
|
|
|
export default function compose<R>(...funcs: Function[]): (...args: any[]) => R
|
|
|
|
export default function compose(...funcs: Function[]) {
|
|
if (funcs.length === 0) {
|
|
// infer the argument type so it is usable in inference down the line
|
|
return <T>(arg: T) => arg
|
|
}
|
|
|
|
if (funcs.length === 1) {
|
|
return funcs[0]
|
|
}
|
|
|
|
return funcs.reduce(
|
|
(a, b) =>
|
|
(...args: any) =>
|
|
a(b(...args))
|
|
)
|
|
}
|