<br><br><div class="gmail_quote">2011/11/24 <span dir="ltr"><<a href="mailto:beginners-request@haskell.org">beginners-request@haskell.org</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
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Today's Topics:<br>
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1. Basic "data" question (Costello, Roger L.)<br>
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Message: 1<br>
Date: Thu, 24 Nov 2011 10:43:58 +0000<br>
From: "Costello, Roger L." <<a href="mailto:costello@mitre.org">costello@mitre.org</a>><br>
Subject: [Haskell-beginners] Basic "data" question<br>
To: "<a href="mailto:beginners@haskell.org">beginners@haskell.org</a>" <<a href="mailto:beginners@haskell.org">beginners@haskell.org</a>><br>
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Hi Folks,<br>
<br>
I am trying to define a data type for this:<br>
<br>
A Lambda term is one of these:<br>
- Variable<br>
- Application of a Lambda term to a Lambda term<br>
- Abstraction of a Variable in a Lambda term<br>
<br>
Here's an example of a Lambda term:<br>
<br>
term = Abstraction (Variable X) (Application (Variable X) (Variable Y))<br>
<br>
Is there a way to define Lambda term?<br>
<br>
Here's an attempt at defining it:<br>
<br>
data Var = V | W | X | Y | Z<br>
<br>
data Lambda = Variable Var | Application Lambda Lambda | Abstraction (Variable Var) Lambda<br>
<br>
But that yields the following error:<br>
<br>
test.hs:5:71: Not in scope: type constructor or class 'Variable'<br>
<br>
Any suggestions would be much appreciated.<br>
<br>
/Roger<br>
<br>
<br>
<br>
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End of Beginners Digest, Vol 41, Issue 33<br>
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</blockquote></div><font color="#222222" face="arial, sans-serif">value constructor followed by types.</font> And (Variable Var) <h3 class="r" style="font-size: medium; font-weight: normal; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; line-height: 1; overflow-x: hidden; overflow-y: hidden; text-overflow: ellipsis; white-space: nowrap; color: rgb(34, 34, 34); font-family: arial, sans-serif; background-color: rgb(255, 255, 255); ">
belong to <span style="background-color: transparent; ">Lambda type.</span></h3><div><span style="background-color: transparent; "><br></span></div><div>Could define like this:</div><div>data Lambda var= Variable var | Application (Lambda var) (Lambda var)</div>
<div><br></div><div>var be any types</div>