compose.ts

import { compose } from 'redux'

// adapted from DefinitelyTyped/compose-function

const numberToNumber = (a: number): number => a + 2
const numberToString = (a: number): string => 'foo'
const stringToNumber = (a: string): number => 5

const t1: number = compose(
  numberToNumber,
  numberToNumber
)(5)
const t2: string = compose(
  numberToString,
  numberToNumber
)(5)
const t3: string = compose(
  numberToString,
  stringToNumber
)('f')
const t4: (a: string) => number = compose(
  (f: (a: string) => number) => (p: string) => 5,
  (f: (a: number) => string) => (p: string) => 4
)(numberToString)

const t5: number = compose(
  stringToNumber,
  numberToString,
  numberToNumber
)(5)
const t6: string = compose(
  numberToString,
  stringToNumber,
  numberToString,
  numberToNumber
)(5)

// rest signature
const t7: string = compose<string>(
  numberToString,
  numberToNumber,
  stringToNumber,
  numberToString,
  stringToNumber
)('fo')

const multiArgFn = (a: string, b: number, c: boolean): string => 'foo'

const t8: string = compose(multiArgFn)('bar', 42, true)
const t9: number = compose(
  stringToNumber,
  multiArgFn
)('bar', 42, true)
const t10: string = compose(
  numberToString,
  stringToNumber,
  multiArgFn
)('bar', 42, true)

const t11: number = compose(
  stringToNumber,
  numberToString,
  stringToNumber,
  multiArgFn
)('bar', 42, true)

const funcs = [stringToNumber, numberToString, stringToNumber]
const t12 = compose(...funcs)('bar')