From: divyanshu ranjan <idivyanshu.ranjan@gmail.com>
To: doaltan <doaltan@yahoo.co.uk>; The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell <beginners@haskell.org>
Sent: Tuesday, 12 March 2013, 12:53
Subject: Re: [Haskell-beginners] Writing a custom pop function for a stack data type
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
<doaltan@yahoo.co.uk> wrote:
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.
_______________________________________________
Beginners mailing list
Beginners@haskell.org
http://www.haskell.org/mailman/listinfo/beginners