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Daryoush Mehrtash | 10 Oct 2012 22:53
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Is there a tool to see reduction steps?

I have been given a piece of code that uses Tie-ing the Knot concept to label a tree of nodes in breath first manner.  It seems to work fine, but  I am having trouble expanding the code on my own to see the evaluation  process.   I like to know if there is a tools to use to see the reduction steps. 





data Tree = Leaf | Node Tree Int Tree deriving Show
 
label (Node ln _ rn) ((h:r):rest) = (Node lr h rr, r:r2) where
                                        (lr, r1) = label ln rest
                                        (rr, r2) = label rn r1
label _ _  = (Leaf, [])
lt t = let (r, unused) = label t ([1..]:unused)
       in r




--
Daryoush

Weblog:  http://onfp.blogspot.com/
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Ozgur Akgun | 10 Oct 2012 23:12
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Re: Is there a tool to see reduction steps?

Hi Daryoush,


You could add another case to label, importing Debug.Trace:

data Tree = Leaf | Node Tree Int Tree deriving Show

label t | trace (show $ "label " ++ show t) False = undefined
label (Node ln _ rn) ((h:r):rest) = (Node lr h rr, r:r2) where
                                        (lr, r1) = label ln rest
                                        (rr, r2) = label rn r1
label _ _  = (Leaf, [])
lt t = let (r, unused) = label t ([1..]:unused)
       in r

This will output one line per each call to label. Except for one thing: your show function will never actually terminate, if the tree is cyclic. You can fix this by defining your own show function.

HTH,
Ozgur

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Thomas Horstmeyer | 17 Oct 2012 10:39
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Re: Is there a tool to see reduction steps?

There is Hood [11 and its graphical front-end GHood [2]. I have never 
used them myself however, only seen them demonstrated. Normally, using 
Debug.Trace is enough for me.

[1] http://www.ittc.ku.edu/csdl/fpg/Tools/Hood
[2] http://community.haskell.org/~claus/GHood/

Thomas

Am 10.10.2012 22:53, schrieb Daryoush Mehrtash:
> I have been given a piece of code that uses Tie-ing the Knot concept to
> label a tree of nodes in breath first manner.  It seems to work fine,
> but  I am having trouble expanding the code on my own to see the
> evaluation  process.   I like to know if there is a tools to use to see
> the reduction steps.
>
>
>
>
>     data Tree = Leaf | Node Tree Int Tree deriving Show
>
>     label (Node ln _ rn) ((h:r):rest) = (Node lr h rr, r:r2) where
>                                              (lr, r1) = label ln rest
>                                              (rr, r2) = label rn r1
>     label _ _  = (Leaf, [])
>     lt t = let (r, unused) = label t ([1..]:unused)
>             in r
>
>
>
>
>
> --
> Daryoush
>
> Weblog: http://onfp.blogspot.com/
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe <at> haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
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Gmane