[Haskell-cafe] Stack ADT?

[Richard O'Keefe]

On Feb 5, 2010, at 6:38 AM, Casey Hawthorne wrote:

> On Thu, 4 Feb 2010 09:07:28 -0800 (PST), you wrote:
>
>> Can't find a Stack datatype on Hoogle? Where should I look?
>>
>> Michael
>> module Stack(Stack,push,pop,top,emptyStack,stackEmpty) where
...

Or just use a list.

A more Haskellish approach to stacks than using "pop" and "top"
would be something like this:

	newtype Stack t = [t]

	emptyStack = Stack []

	stackPush (Stack s) = Stack (x:s)

	viewStack (Stack []) = Nothing
	viewStack (Stack (top:rest)) = Just (top, Stack rest)
	
Instead of
	if stackEmpty s then ... else ... top s ... pop s ...
do
	case viewStack s of
	    Nothing -> ...
	    Just (top, rest) -> ...

Note that none of the functions in this interface can fail.

>