Pascal's Triangle in Coffeescript

pascal-original.coffee

module.exports = (rows) ->
    result = []
    for n in [0..rows]
      if n is 0
        result[n] = [1]
      else
        previous = new Array().concat 0, result[n-1], 0
        current = []
        for val, idx in previous
          sum = val + previous[idx+1]
          current.push sum unless isNaN(sum)
        result[n] = current
    result

pascal-refactored.coffee

module.exports = (rows, results = null) ->
  if results is null
    arguments.callee rows, [[1]]
  else if results.length > rows
    results
  else
    previous = [].concat 0, results[results.length-1], 0
    results.push (previous.map (val, idx) ->
      val + previous[idx+1]
    ).filter (val, idx) -> !isNaN(val)
    arguments.callee rows, results

pascal-spec.coffee

pascal = require './pascal'

describe 'Pascal', ->
  it 'should return 1 for 0', ->
    result = pascal 0
    expect(result.length).toBe 1
    expect(result[0]).toEqual [1]

  it 'should return correctly for 1', ->
    result = pascal 1
    expect(result.length).toBe 2
    expect(result[1]).toEqual [1,1]

  it 'should return correctly for 2', ->
    result = pascal 2
    expect(result.length).toBe 3
    expect(result[2]).toEqual [1,2,1]

  it 'should return correctly for 3', ->
    result = pascal 3
    expect(result.length).toBe 4
    expect(result[3]).toEqual [1,3,3,1]

  it 'should return correctly for 4', ->
    result = pascal 4
    expect(result.length).toBe 5
    expect(result[4]).toEqual [1,4,6,4,1]

  it 'should return correctly for 5', ->
    result = pascal 5
    expect(result.length).toBe 6
    expect(result[5]).toEqual [1,5,10,10,5,1]