Implementation of a merge sort

merge.coffee

PASSED = 0

check_sorted = (was, now) ->
  if !now.reduce ((a,c,i) -> a && (!now[i+1]? || now[i] < now[i+1])), true
    throw new Error """\n
    Was: [#{was}]
    Now: [#{now}]\n"""
  else
    ++PASSED

Array::shuffle = ->
  r = []; iss = [0..@length - 1]
  while iss[0]?
    i = Math.floor(Math.random()*iss.length)
    r.push @[iss.splice i, 1]
  r
  
Array::mergeSort = ->
  conquer = (p, q, r) =>
    while p <= q && q < r
      if @[p++] > @[q+1]
        @splice (p-1), 0, (@splice (q++ +1), 1)[0]
  divide = (p = 0, r = @length - 1) =>
    if p < r
      q = Math.floor (p + r)/2
      divide  p,    q
      divide  q+1,  r
      conquer p, q, r
  do divide; @

for i in [1..5000]
  sample = [1..Math.ceil(Math.random()*20)].shuffle()
  check_sorted sample[..], sample.mergeSort()
console.log "PASSED #{PASSED} tests."