State Monad in CoffeeScript

state-monad.coffee

push = (element) -> (stack) ->
  newStack = [element].concat stack
  {value: element, stack: newStack}

pop = (stack) ->
  element = stack[0]
  newStack = stack.slice 1
  {value: element, stack: newStack}

bind = (stackOperation, continuation) -> (stack) ->
  result = stackOperation stack
  (continuation result.value) result.stack

result = (value) -> (stack) ->
  {value: value, stack: stack}

initialStack = []

computation1 = bind \
  (push 4), -> bind \
  (push 5), -> bind \
  pop, (a)  -> bind \
  pop, (b)  ->
    result a + ":" + b

computation2 = bind \
  (push 2), -> bind \
  (push 3), -> bind \
  pop, (a)  -> bind \
  pop, (b)  ->
    result a + ":" + b

composed = bind \
  computation1, (a) -> bind \
  computation2, (b) ->
    result a + ":" + b

finalResult = composed initialStack
console.log finalResult.value