[Haskell-cafe] Stack ADT?

[Daniel Peebles]

>
> data Stack a   = EmptyStk | Stk a (Stack a)


I find it amusing that the book defined a type that is exactly isomorphic to
the standard list (EmptyStk === [] and Stk === (:)). I guess it's just for
clarity?

On Thu, Feb 4, 2010 at 12:29 PM, Casey Hawthorne <caseyh at istar.ca> 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
> >
>
>
> From "Algorithms: a functional programming approach"
> Second edition
> Fethi Rabhi
> Guy Lapalme
>
>
> data Stack a                    = EmptyStk
>                                                                        |
> Stk a (Stack a)
>
> push x s                                        = Stk x s
>
> pop EmptyStk                    = error "pop from an empty stack"
> pop (Stk _ s)           = s
>
> top EmptyStk                    = error "top from an empty stack"
> top (Stk x _)           = x
>
> emptyStack                              = EmptyStk
>
> stackEmpty EmptyStk = True
> stackEmpty _                            = False
>
>
>
>
> newtype Stack a         = Stk [a]
>
> push x (Stk xs)         = Stk (x:xs)
>
> pop (Stk [])                    = error "pop from an empty stack"
> pop (Stk (_:xs))        = Stk xs
>
> top (Stk [])                    = error "top from an empty stack"
> top (Stk (x:_))         = x
>
> emptyStack                              = Stk []
>
> stackEmpty (Stk []) = True
> stackEmpty (Stk _ ) = False
>
>
> --
> Regards,
> Casey
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