Hi Tamas There are several ways to debug a Haskell program. The most advanced ones are based in offline analysis of traces, I think Hat [1] is the most up-to-date tool for this. There is a Windows port of Hat at [5]. Another approach is to simply use Debug.Trace. A more powerful alternative for this approach is Hood [2]. Even if it hasn't been updated in some time, Hood works perfectly with the current ghc distribution. Even more, Hugs has it already integrated [3]. You can simply import Observe and use observations directly in your program. For instance: import Observe f' = observe "f" f f a b = .... And then in hugs the expression:
f' 1 2
would output what you want.
Finally, the GHCi debugger project [4] aims to bring dynamic
breakpoints and intermediate values observation to GHCi in a near
future. Right now the tool is only available from the site as a
modified version of GHC, so unfortunately you will have to compile it
yourself if you want to try it.
Cheers
pepe
1. www.haskell.org/hat
2. www.haskell.org/hood
3. http://cvs.haskell.org/Hugs/pages/users_guide/observe.html
4. http://haskell.org/haskellwiki/GHC/GHCiDebugger
5. http://www-users.cs.york.ac.uk/~ndm/projects/windows.php
On 06/09/06, Tamas K Papp
Hi,
I would like to learn a reasonable way (ie how others do it) to debug programs in Haskell. Is it possible to "see" what's going on when a function is evaluated? Eg in
f a b = let c = a+b d = a*b in c+d
evaluating
f 1 2
would output something like
f called with values 1 2 c is now (+) a b => (+) 1 2 => 3 d is now (*) a b => (*) 1 2 => 2 ...
Or maybe I am thinking the wrong way, and functional programming has its own debugging style...
Thanks,
Tamas _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe