Using a stack inside a Haskell Function - function

Question

I want to use a stack inside a Haskell function but I don't know how to use it. My function is supposed to work like this :
Take a string
Put some elements of this input string to output string and put others to stack.
Pop elements to that output string too.
Do 2 and 3 recursively until stack is empty.
Print the output string when stack is empty.
I don't know when and where to create that stack. I couldn't figure it out myself since I'm very new at Haskell programming. Since I haven't created any code I can't show any code either. Can you tell me what the function will look like in an algorithmic way? Where should I define the stack and output string? Thanks.

Answer 1

One comfortable thing here is that standard Haskell list is a fine stack (natural, bearing in mind that stack is a more restricted kind of list). Your function might look something like this:
--takes one string and uses a stack to convert it to another string
doSomethingWithStack :: String -> [String] -> String
doSomethingWithStack str stack =
let str' = --here you embody your points 2 and 3
stack' = --stack top is (head stack), push is (x : stack), pop is (tail stack)
--... any change you'd want to make to any value turns into a new variable
in case stack'' of --check the final variables
[] -> str'' --if stack is empty, end
_ -> doSomethingWithStack str'' stack'' --if not, repeat
--now, to make it pretty
fancyWrapper :: String -> String
fancyWrapper str = doSomethingWithStack str [] -- empty list is an empty stack
--because you should strive to separate pure and impure functions
--, I suggest that you do the print elsewhere, say
main = do
str <- getLine
print $ fancyWrapper str
Hopefully that is neither too little nor too much. Give it a try and ask more specific questions, once you run into problems.