Re: [Haskell-cafe] how do you debug programs?
On Wed, Sep 06, 2006 at 11:34:05AM +0200, Pepe Iborra wrote: 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. Dear Pepe, Thank you for the information. I finally ended up working with Debug.Trace, and found the bug very quickly. I also tried Hood, but couldn't load it in ghci: import Observe can't find the library, but % locate Observe /usr/lib/ghc-6.4.2/hslibs-imports/util/Observe.hi /usr/lib/ghc-6.4.2/hslibs-imports/util/Observe.p_hi /usr/lib/hugs/libraries/Hugs/Observe.hs /usr/lib/hugs/oldlib/Observe.hs Does importing from hslibs-imports require something special? Quite a bit of philosophical discussion erupted as a result of my original question. I understand the arguments of those who dislike debuggers, but I don't think I could have done without some debugging. It turns out that the problem was not in the algorithm, but in the specification of the equation itself. I was solving a continuous time Hamilton-Jacobi-Bellman equation, and there was a point in the state space where the supremum was infinity, giving stuff like 0/Inf and their ilk. I respecified the problem and now it works. For those who think that it is always possible to break the problem up into small pieces you can test individually (without a debugger): you can't, at least not when solving functional equations. The corner cases (and nonconvergence, when using non-contraction methods, such as PEA) are difficult to catch and reproduce. Thanks for all the suggestions, Tamas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how do you debug programs?
On 07/09/2006, at 10:53, Tamas K Papp wrote: Dear Pepe, Thank you for the information. I finally ended up working with Debug.Trace, and found the bug very quickly. I also tried Hood, but couldn't load it in ghci: import Observe can't find the library, but % locate Observe /usr/lib/ghc-6.4.2/hslibs-imports/util/Observe.hi /usr/lib/ghc-6.4.2/hslibs-imports/util/Observe.p_hi /usr/lib/hugs/libraries/Hugs/Observe.hs /usr/lib/hugs/oldlib/Observe.hs Does importing from hslibs-imports require something special? Hi Tamas I'm glad to hear that you fixed it! GHC includes Observe (the hs-libs-imports file you are seeing) only in the hidden 'util' package, which I believe is deprecated or not present in 6.6. If you want to use it, launch ghci with the flag '- package util'. Or download Observe.hs from the Hood website and place it somewhere in the path. Hmm, it would be handy to have a Cabal Hood package... Cheers pepe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how do you debug programs?
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 [EMAIL PROTECTED] wrote: 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how do you debug programs?
mnislaih: 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. Pepe, would you like to put up a page on the haskell.org wiki about debugging in Haskell? You could use the above mail as a start :) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how do you debug programs?
Thanks for the suggestion Don, I started the wiki page at http://haskell.org/haskellwiki/Debugging On 06/09/06, Donald Bruce Stewart [EMAIL PROTECTED] wrote: mnislaih: 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. Pepe, would you like to put up a page on the haskell.org wiki about debugging in Haskell? You could use the above mail as a start :) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
