Good morning, I sent a previous email to you in regard to this - if my request is rejected, will I be notified? I'm reading the book "Developing Web Applications with Haskell and Yesod". It is a very interesting read and I'm hoping to be able to be able to put up a simple web app using it as a result. I was wondering if anyone has had experience with it. Thank you On Mar 12, 2013, at 9:21 AM, beginners-request@haskell.org wrote:

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Today's Topics:

1. Re: Writing a custom pop function for a stack data type (doaltan) 2. Re: Writing a custom pop function for a stack data type (Brent Yorgey) 3. Re: Suspend/resume computation using Cont monad and callCC (Ertugrul S?ylemez) 4. Re: Writing a custom pop function for a stack data type (Emanuel Koczwara) 5. Re: Performance problem with Haskell/OpenGL/GLFW (Jesper S?rnesj?)

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Message: 1 Date: Tue, 12 Mar 2013 11:06:35 +0000 (GMT) From: doaltan Subject: Re: [Haskell-beginners] Writing a custom pop function for a stack data type To: divyanshu ranjan Cc: "beginners@haskell.org" Message-ID: <1363086395.38137.YahooMailNeo@web171402.mail.ir2.yahoo.com> Content-Type: text/plain; charset="iso-8859-1"

Actually I'm getting the error with this :

data Stack = Empty | Elem Char Stack deriving Show

pophead :: Stack -> Char pophead Empty = Empty pophead (Elem x stack) = x

________________________________ From: divyanshu ranjan To: doaltan ; The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell 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 wrote:

Hi I have such a stack data structure:?

...

datamystack =Empty |Elem Char mystack derivingShow

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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