FP solve the Change Problem

change_problem.coffee

#
# FP solve the Change Problem
#  eg. myChange = calcChange(cost, myPayment)
#

# Used in fold() to build change object
#  Should be nested in calcChange, but is lifted for cleanliness
coinAccStructure = (acc, coin) ->
  change         = acc["payment"]
  acc[coin]      = change % coin
  acc["payment"] = change / coin
  acc

# Curried calculator
calcChange = (coins) -> (cost, payment) ->
  coins.fold(coinAccStructure, {"payment": payment}).omit "payments"

# Initalisated calculator for Australian coins
auCoins = [2, 1, .5, .2, .1, .05]
calcAuChange = calcChange(auCoins)

# Use
cost    = 5.20
payment = 10.00
change  = calcAuChange(cost, payment)

Had a crack at it this morning, take a look at my fork.