Re: [Haskell-beginners] Beginners Digest, Vol 41, Issue 33

2011/11/24

Send Beginners mailing list submissions to beginners@haskell.org

To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/beginners or, via email, send a message with subject or body 'help' to beginners-request@haskell.org

You can reach the person managing the list at beginners-owner@haskell.org

When replying, please edit your Subject line so it is more specific than "Re: Contents of Beginners digest..."

Today's Topics:

1. Basic "data" question (Costello, Roger L.)

----------------------------------------------------------------------

Message: 1 Date: Thu, 24 Nov 2011 10:43:58 +0000 From: "Costello, Roger L." Subject: [Haskell-beginners] Basic "data" question To: "beginners@haskell.org" Message-ID: Content-Type: text/plain; charset="us-ascii"

Hi Folks,

I am trying to define a data type for this:

A Lambda term is one of these: - Variable - Application of a Lambda term to a Lambda term - Abstraction of a Variable in a Lambda term

Here's an example of a Lambda term:

term = Abstraction (Variable X) (Application (Variable X) (Variable Y))

Is there a way to define Lambda term?

Here's an attempt at defining it:

data Var = V | W | X | Y | Z

data Lambda = Variable Var | Application Lambda Lambda | Abstraction (Variable Var) Lambda

But that yields the following error:

test.hs:5:71: Not in scope: type constructor or class 'Variable'

Any suggestions would be much appreciated.

/Roger

------------------------------

_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

End of Beginners Digest, Vol 41, Issue 33 *****************************************

value constructor followed by types. And (Variable Var) belong to Lambda type. Could define like this: data Lambda var= Variable var | Application (Lambda var) (Lambda var) var be any types