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Today's Topics:
1. Basic "data" question (Costello, Roger L.)
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Message: 1
Date: Thu, 24 Nov 2011 10:43:58 +0000
From: "Costello, Roger L." <[email protected]>
Subject: [Haskell-beginners] Basic "data" question
To: "[email protected]" <[email protected]>
Message-ID:
<[email protected]>
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
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