You have declared new data type mystack not Stack, so haskell compiler
could not find Stack data type and its constructors. Secondly data type in
Haskell need to be start with capital letters like
data Mystack = Empty | Elem Char Mystack deriving Show
then correct Function definition is
pophead :: Mystack -> Char
Regards
Divyanshu
On Tue, Mar 12, 2013 at 4:12 PM, doaltan
Hi I have such a stack data structure:
data mystack = Empty | Elem Char mystack deriving Show
I'm trying to get the head of the stack using this: pophead :: Stack -> Char pophead Empty = Empty pophead (Element x stack) = x And I'm getting this error for the last sentence of the function :
Not in scope: data constructor `Stack' Can you tell me how to fix it? Thanks.
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