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to Accumulate in the CoffeeScript Track

Published at Jul 13 2018 · 0 comments
Test suite


This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Implement the accumulate operation, which, given a collection and an operation to perform on each element of the collection, returns a new collection containing the result of applying that operation to each element of the input collection.

Given the collection of numbers:

  • 1, 2, 3, 4, 5

And the operation:

  • square a number (x => x * x)

Your code should be able to produce the collection of squares:

  • 1, 4, 9, 16, 25

Check out the test suite to see the expected function signature.


Keep your hands off that collect/map/fmap/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.

Refer to the Exercism CoffeScript page for getting started with CoffeeScript.

In order to run the test, you can run the test file from the exercise directory:

jasmine-node --coffee .


Conversation with James Edward Gray II https://twitter.com/jeg2

Submitting Incomplete Solutions

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require './accumulate'

describe '[].accumulate()', ->

  it 'empty accumulation', ->
    accumulator = (e) -> e * e
    expect([].accumulate(accumulator)).toEqual []

  xit 'accumulate squares', ->
    accumulator = (number) -> number * number
    expect([1, 2, 3].accumulate accumulator).toEqual [1, 4, 9]

  xit 'accumulate upcases', ->
    accumulator = (word) -> word.toUpperCase()
    result      = 'hello world'.split(/\s/).accumulate accumulator

    expect(result).toEqual ['HELLO', 'WORLD']

  xit 'accumulate reversed strings', ->
    accumulator = (word) -> word.split('').reverse().join('')
    result      = 'the quick brown fox etc'.split(/\s/).accumulate accumulator

    expect(result).toEqual ["eht", "kciuq", "nworb", "xof", "cte"]

  xit 'accumulate recursively', ->
    result = 'a b c'.split(/\s+/).accumulate (char)  ->
      '1 2 3'.split(/\s+/).accumulate (digit) -> "#{char}#{digit}"

    expect(result).toEqual([["a1", "a2", "a3"], ["b1", "b2", "b3"], ["c1", "c2", "c3"]])
Array::accumulate = (accumulator) ->
  for i in this
    i = accumulator i

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