Re: [Haskell-beginners] exceptions and stacks

From what I can tell on the link that I found, the person ended up using a

well studying it further it seems the output I got was: TvChannelsParse: Prelude.head: empty list It was a bit difficult to extract it because the normal output of my program is really flooded by extra text from the RTS options. So I get this GHC.List.CAF extra information; not particularly useful (I mean for sure the head fails in GHC.List, I already knew that). I see others got the same as I did: http://www.haskell.org/pipermail/haskell-cafe/2008-February/040053.html So maybe there is nothing to expect from that profiling trick after all... third party library to track the problem. If there is nothing builtin, I'll just mark head lines in my code to find the culprit, but it really seems wrong and disappointing from a modern language if there is no better way. emmanuel On Tue, Nov 6, 2012 at 10:37 PM, Emmanuel Touzery wrote:

so in the end I had to build the program with:

ghc -prof -auto-all -rtsopts -osuf prof *.hs

so also -rtsopts. After the simple ghc *.hs build.

then I run it with:

+RTS -xc -RTS

in the command-line.

but it doesn't appear to work properly, I guess I didn't quite compile or run it correctly. It constantly displays me some stack position during the whole runtime even when there is no problem. When the real problem comes, it still displays the same stack it did for the whole runtime, but there is no "head" in that function.

I'll probably end up debugging this one "by hand", but I would really would like to have a general solution for the problem for the future, where tooling would help me...

annotating/modifying my code... it really seems wrong in this case :-/

On Tue, Nov 6, 2012 at 8:34 PM, Emmanuel Touzery wrote:

...

well it certainly requires will to build with profiling. i had to reinstall all my cabal packages with profiling enabled, which i finally managed to do now..

and now it tells me: ghc -prof -auto-all Prog.hs

Dynamic linking required, but this is a non-standard build (eg. prof). You need to build the program twice: once the normal way, and then in the desired way using -osuf to set the object file suffix.

Ah well.. I'll fight some more with this later. Not exactly "out of the box"...

Emmanuel

On Tue, Nov 6, 2012 at 1:02 PM, Ozgur Akgun wrote:

...

Hi Emmanuel,

It is indeed good practice to write total programs in general. However, I understand the need for stack traces in practice.

There are some slides by Simon Marlow on the issue, ironically using your example in the title.

In short: check the -xc flag in http://www.haskell.org/ghc/docs/7.0.1/html/users_guide/runtime-control.html

Hope this helps, Ozgur