On Wed, Mar 3, 2010 at 6:07 AM, Ivan Miljenovic wrote:

On 3 March 2010 16:06, Tom Hawkins wrote:

...

How do I track down an reference to an undefined value?  My program must not be using a library correctly because the program makes no direct use of 'undefined'.  Running with +RTS -xc yields:

Test: Prelude.undefined

Are you matching all patterns?  When compiling with -Wall does it make any complaints?

-Wall only complains about shadow bindings, defined but not used, and no type signature. But no unmatched patterns.

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com

2010/3/3 Tom Hawkins

On Wed, Mar 3, 2010 at 6:07 AM, Ivan Miljenovic

-Wall only complains about shadow bindings, defined but not used, and no type signature. But no unmatched patterns.

If you can run your code through the ghc debugger you can get it to break when an undefined exception is raised. The options are :set -fbreak-on-exception or -fbreak-on-error. More info in the documentation at http://www.haskell.org/ghc/docs/latest/html/users_guide/ghci-debugger.html#g... Hope that helps, Alex MDC

On Wed, Mar 3, 2010 at 6:15 AM, Ivan Miljenovic wrote:

On 3 March 2010 16:11, Tom Hawkins wrote:

...

-Wall only complains about shadow bindings, defined but not used, and no type signature.  But no unmatched patterns.

Yes it does: one of the options it brings in is -fwarn-incomplete-patterns which tells you if you've missed a pattern match.

http://www.haskell.org/ghc/docs/latest/html/users_guide/options-sanity.html

I think he meant that it doesn't because he doesn't have any :)

Ivan Miljenovic writes:

...

Test: Prelude.undefined

Are you matching all patterns? When compiling with -Wall does it make any complaints?

How would this help? 'Prelude.undefined' happens because somewhere you're trying to evaluate a value defined with that particular literal, doesn't it? Using this in a library seems to me to be in poor taste, but grepping the code should reveal it, if you're sure that's where the problem is hiding. I generally replace any 'undefined's with 'error string', with each 'string' unique for that position. -k -- If I haven't seen further, it is by standing in the footprints of giants

On Wed, Mar 3, 2010 at 7:24 AM, Alexander Dunlap wrote:

On Tue, Mar 2, 2010 at 9:06 PM, Tom Hawkins wrote:

...

How do I track down an reference to an undefined value?  My program must not be using a library correctly because the program makes no direct use of 'undefined'.  Running with +RTS -xc yields:

While the debugger, etc., are very useful tools, I find that often the easiest way to track down this sort of bug is to test your code function-by-function.

The debugger was not that helpful, so I may have to resort to this. Is there any work being done to improve reporting for these type of errors? It seems to be a fairly common problem.

Tom Hawkins wrote:

The debugger was not that helpful, so I may have to resort to this.

Is there any work being done to improve reporting for these type of errors? It seems to be a fairly common problem.

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