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Today's Topics:
1. Haskell's Scrap Your Boilerplate (SYB) - applying
transformation only once instead of everywhere (Duc le anh)
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Message: 1
Date: Tue, 4 Jun 2013 00:31:31 -0700
From: Duc le anh <[email protected]>
Subject: [Haskell-beginners] Haskell's Scrap Your Boilerplate (SYB) -
applying transformation only once instead of everywhere
To: [email protected]
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What's the best way to apply a transformation to a tree only once instead
of everywhere using SYB? For instance, in the following simplified
expression, there are several instances of Var "x", and I want to replace
the first instance with Var "y" only.
data Exp = Var String | Val Int | Plus Exp Exp |...
myExp = Val 5 `Plus` Var "x" `Plus` Val 5 `Plus` Var "x" ...
This can't be done using the everywhere combinator since it will try to
transform all instances of Var "x" toVar "y".
--
Duc A. Le
PS: I also asked this on stackoverflow but figured that I might get a
faster response here. Thank you!
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