CoffeeScript contracts

contracts.coffee

guardArgs = (def, args) ->
  i = 0
  for arg, type of def
    throw new Error("bad type of #{arg}") unless typeof args[i] == type
    i++

typeEnsure = (def, f) -> ->
  guardArgs(def, arguments)
  f.apply @, arguments
    
myFunc = typeEnsure {name: 'string', i: 'number'}, (name, i) ->
  console.log name, i

myFunc("foo", 1) # ok
myFunc("foo", "x") # Error: bad type of i