> What's going on here? I'm not even calling function POP. > *Data.Stack> let s2 = pop s1 > *Data.Stack> top s2 > *** Exception: Stack.hs:8:0-28: Non-exhaustive patterns in function pop
Haskell being a non strict language, does not evaluate pop s1 when you define let s2 = pop s1. but when you try to use s2 by evaluating "top s2" "pop s1" needs to be evaluated leading to the error in "pop", since the definition of pop, does not deal with the case when the Stack is empty (Stack []). > pop (Stack (_:xs)) = Stack xs > top (Stack (x:_)) = x _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
