reduce-spec.ts

import { reduce } from 'rambda'

describe('reduce', () => {
  it('happy', () => {
    const result = reduce<number, number>(
      (acc, elem) => {
        acc // $ExpectType number
        elem // $ExpectType number
        return acc + elem
      },
      1,
      [ 1, 2, 3 ]
    )

    result // $ExpectType number
  });

  it('with two types', () => {
    const result = reduce<number, string>(
      (acc, elem) => {
        acc // $ExpectType string
        elem // $ExpectType number

        return `${acc}${elem}`
      },
      'foo',
      [ 1, 2, 3 ]
    )

    result // $ExpectType string
  });

  it('with index', () => {
    const result = reduce<number, number>(
      (acc, elem, i) => {
        acc // $ExpectType number
        elem // $ExpectType number
        i // $ExpectType number
        return acc + elem
      },
      1,
      [ 1, 2, 3 ]
    )

    result // $ExpectType number
  });

  it('fallback', () => {
    const result = reduce((acc, val) => {
      acc // $ExpectType number
      return acc + val
    }, 1,[ 1, 2, 3 ])

    result // $ExpectType number
  });

  it('fallback with index', () => {
    const result = reduce((acc, val, i) => {
      acc // $ExpectType number
      i // $ExpectType number
      return acc + val
    }, 1,[ 1, 2, 3 ])

    result // $ExpectType number
  });

  it('fallback with two types', () => {
    const result = reduce((acc, val) => {
      acc // $ExpectType string
      return acc + val
    }, 'foo',[ 1, 2, 3 ])

    result // $ExpectType string
  });
});