some way to reverse engineer lambda expressions out of the debugger?

tphyahoo

30 Dec 2006 30 Dec '06

3:53 a.m.

I am a newbie learning haskell. (First forum post.) I am wondering if there is a trick to get debugging information about functions out of the environment (which for me, for now, is ghci). In this example, *UnixTools> :t map (*) [1,2] map (*) [1,2] :: (Num a) => [a -> a] This is very nice, but I would *really* like to see something like *UnixTools> explodeLambda( map (*) [1,2] ) [(\x -> 1*x),(\x -> 2*x)] Yes, maybe I'm dreaming, but I would like haskell to reverse engineer / pretty print lambda expressions for me. (Note that: *UnixTools> map ($ 5 ) [(\x -> 1*x),(\x -> 2*x)] [5,10] *UnixTools> map ($ 5) ( map (*) [1..2] ) [5,10] So these expressions really are the same, only it could be argued that the first expression is in some sense easier to read if you are debugging something complex. ) I would like to have something like "Data::Dumper" from perl, but of course, on steroids. Is something like this possible, or be worked on? Or probably never going to happen? Cheers, thomas. -- View this message in context: http://www.nabble.com/some-way-to-reverse-engineer-lambda-expressions-out-of... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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dons＠cse.unsw.edu.au

1 Jan 1 Jan

2:46 a.m.

New subject: some way to reverse engineer lambda expressions out of the debugger?

tphyahoo:

...

I am a newbie learning haskell. (First forum post.)

I am wondering if there is a trick to get debugging information about functions out of the environment (which for me, for now, is ghci).

In this example,

*UnixTools> :t map (*) [1,2] map (*) [1,2] :: (Num a) => [a -> a]

This is very nice, but I would *really* like to see something like

*UnixTools> explodeLambda( map (*) [1,2] ) [(\x -> 1*x),(\x -> 2*x)]

Yes, maybe I'm dreaming, but I would like haskell to reverse engineer / pretty print lambda expressions for me.

You can use 'hat' to trace/reduce expressions. http://www.cs.york.ac.uk/fp/hat/ The new ghci debugger can print closures too, but I'm not sure if it does what you want. All very possible, maybe a little experimental though. -- Don

Bulat Ziganshin

6:01 a.m.

New subject: some way to reverse engineer lambda expressions out of the debugger?

Hello tphyahoo, Saturday, December 30, 2006, 11:53:53 AM, you wrote:

...

*UnixTools> explodeLambda( map (*) [1,2] ) [(\x ->> 1*x),(\x -> 2*x)]

i'm wondering whether it's possible to use typeclasses to implement this, like packages for symbolic computations (afair, it was demonstrated by Oleg) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

Malcolm Wallace

11 Jan 11 Jan

12:26 p.m.

New subject: some way to reverse engineer lambda expressions out of the debugger?

Bulat Ziganshin wrote:

...

tphyahoo wrote:

...
*UnixTools> explodeLambda( map (*) [1,2] ) [(\x ->> 1*x),(\x -> 2*x)]

Have a play with this, from Claus Reinke: http://www.cs.kent.ac.uk/people/staff/cr3/toolbox/haskell/R.hs Regards, Malcolm

Thomas Hartman

1:10 p.m.

New subject: some way to reverse engineer lambda expressions out of the debugger?

Looks very nice! However, I'm doing my learning on ghci and got an error when I tried to load it. Is this hugs only, or should I try harder? 2007/1/11, Malcolm Wallace :

...

Bulat Ziganshin wrote:

...
tphyahoo wrote:

...
*UnixTools> explodeLambda( map (*) [1,2] ) [(\x ->> 1*x),(\x -> 2*x)]

Have a play with this, from Claus Reinke: http://www.cs.kent.ac.uk/people/staff/cr3/toolbox/haskell/R.hs

Regards, Malcolm _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Claus Reinke

1:47 p.m.

New subject: some way to reverse engineer lambda expressionsout of the debugger?

...

Looks very nice!

thanks!-) it is far from a full-blown solution to the question in the subject, but it has its uses.

...

However, I'm doing my learning on ghci and got an error when I tried to load it.

Is this hugs only, or should I try harder?

I was using Hugs when I wrote that, but it works in GHC almost as well. the error message really ought to point to the option needed, which is -fglasgow-exts if you don't want to set the options by hand, just add the following pragma to the top of R.hs: {-# OPTIONS_GHC -fglasgow-exts #-} more annoying is that ghci will ignore the default directive, so you'll need to give explicit types when you want representations: *Main> foldr (+) 0 [1..4] 10 *Main> foldr (+) 0 [1..4] :: R Int (1 + (2 + (3 + (4 + 0)))) *Main> map (*) [1,2] <interactive>:1:0: No instance for (Show (t -> t)) arising from use of `print' at <interactive>:1:0-12 Possible fix: add an instance declaration for (Show (t -> t)) In the call (print it) In the expression: print it In a 'do' expression: print it *Main> map (*) [1,2] :: [R Int -> R Int] [\x->(1 * x),\x->(2 * x)] claus

...

2007/1/11, Malcolm Wallace :

...
Bulat Ziganshin wrote:

...
tphyahoo wrote:

...
*UnixTools> explodeLambda( map (*) [1,2] ) [(\x ->> 1*x),(\x -> 2*x)]

Have a play with this, from Claus Reinke: http://www.cs.kent.ac.uk/people/staff/cr3/toolbox/haskell/R.hs

Regards, Malcolm _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Thomas Hartman

12 Jan 12 Jan

3:02 a.m.

New subject: some way to reverse engineer lambda expressionsout of the debugger?

works like a charm :) 2007/1/11, Claus Reinke :

...

...
Looks very nice!

thanks!-)

it is far from a full-blown solution to the question in the subject, but it has its uses.

...
However, I'm doing my learning on ghci and got an error when I tried to load it.

Is this hugs only, or should I try harder?

I was using Hugs when I wrote that, but it works in GHC almost as well. the error message really ought to point to the option needed, which is -fglasgow-exts

if you don't want to set the options by hand, just add the following pragma to the top of R.hs:

{-# OPTIONS_GHC -fglasgow-exts #-}

more annoying is that ghci will ignore the default directive, so you'll need to give explicit types when you want representations:

*Main> foldr (+) 0 [1..4] 10 *Main> foldr (+) 0 [1..4] :: R Int (1 + (2 + (3 + (4 + 0)))) *Main> map (*) [1,2]

<interactive>:1:0: No instance for (Show (t -> t)) arising from use of `print' at <interactive>:1:0-12 Possible fix: add an instance declaration for (Show (t -> t)) In the call (print it) In the expression: print it In a 'do' expression: print it *Main> map (*) [1,2] :: [R Int -> R Int] [\x->(1 * x),\x->(2 * x)]

claus

...
2007/1/11, Malcolm Wallace :

...
Bulat Ziganshin wrote:

...
tphyahoo wrote:

...
*UnixTools> explodeLambda( map (*) [1,2] ) [(\x ->> 1*x),(\x -> 2*x)]

Have a play with this, from Claus Reinke: http://www.cs.kent.ac.uk/people/staff/cr3/toolbox/haskell/R.hs

Regards, Malcolm _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Bulat Ziganshin
Claus Reinke
dons＠cse.unsw.edu.au
Malcolm Wallace
Thomas Hartman
tphyahoo