Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
State Monad in CoffeeScript
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) ->
opResult = stackOperation stack
(continuation opResult.value) opResult.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
@snoble
Copy link

snoble commented Dec 7, 2012

have you considered changing the name of the 'result' variable in 'bind'? it's just that because of coffee's weird scope it might be confusing that there two different 'result' var's here. if the definition of 'result' were to come before 'bind' then they would be the same var

also thanks for making this!

@igstan
Copy link
Author

igstan commented Dec 11, 2012

@snoble I didn't and for a very simple reason. At the time I wasn't aware of this weird scoping CoffeeScript has. I'll edit the gist. Thanks for your suggestion.

@weidagang
Copy link

weidagang commented Oct 10, 2013

Very Cool!

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment