| 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 ====================== [michael@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 <caseyh@istar.ca> wrote:
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