Stack trace on error (and packages)

[Keith Wansbrough]

> 
> Hi,
> 
> Is it possible to persuade ghc/RTS to provide a stack trace (or
> something similar) when an error occurs?  I have some code that is
> generating a runtime error (appears to be due to division by
> almost-zero, provoking very large numbers and then a NaN in a case
> statement when coerced to Double) in a function that is used throughout
> my code - it would be a big help to know which function called the
> function that is generating the error.

Yes.  Compile your program with -prof -auto-all  (you need at least -prof on all modules for the link to work, but -auto-all is only necessary on modules containing functions you want to trace).  This turns on automatic profiling.

Now run your program with the option  `+RTS -xc'   .  This will turn on a cost-centre stack trace, displayed each time your program throws an exception (including runtime errors).

This gives not the program stack (which function demanded which value), but the cost-centre stack (which function called which function which failed), which may or may not be more useful.  The former is only available under `gdb' at the moment, with a very hairy user interface.  You can read about cost centres in chapter 4 of the manual.

My apologies for not having put this properly in the manual yet!

HTH..

--KW 8-)
-- 
Keith Wansbrough <kw217@cl.cam.ac.uk>
http://www.cl.cam.ac.uk/users/kw217/
Cambridge University Computer Laboratory.