Not using Stack for anything, just trying to understand how things can be done in Haskell.
To that end... What's going on here? I'm not even calling function POP. Michael ====================== module Data.Stack (Stack, emptyStack, isEmptyStack, push, pop, top) where newtype Stack a = Stack [a] emptyStack = Stack [] isEmptyStack (Stack xs) = null xs push x (Stack xs) = Stack (x:xs) pop (Stack (_:xs)) = Stack xs top (Stack (x:_)) = x ====================== [mich...@localhost ~]$ ghci Stack.hs GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Data.Stack ( Stack.hs, interpreted ) Ok, modules loaded: Data.Stack. *Data.Stack> let s1 = emptyStack *Data.Stack> top (push 1 s1) 1 *Data.Stack> top (push 2 s1) 2 *Data.Stack> top (push 3 s1) 3 *Data.Stack> let s2 = pop s1 *Data.Stack> top s2 *** Exception: Stack.hs:8:0-28: Non-exhaustive patterns in function pop *Data.Stack> --- On Fri, 2/5/10, Casey Hawthorne <cas...@istar.ca> wrote: From: Casey Hawthorne <cas...@istar.ca> Subject: Re: [Haskell-cafe] Stack ADT? To: haskell-cafe@haskell.org Date: Friday, February 5, 2010, 10:36 AM You could also implement stacks with mutable data structures, e.g. STArray, etc. What do you want to use a stack ADT for? Usually stacks are discussed for pedagogical purposes but usually recursion is used if you need a stack like operation. -- Regards, Casey _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
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