The debugger only instruments interpreted code, so evaluations occurring inside library code do not show up in :trace. This is not a terrible problem in practice, since usually seeing the evaluations occurring in your code is what you need to debug the problem. But since :trace is not showing you any evaluations at all, I wonder if the problem might be that your code is not interpreted. In order to ensure that it is, delete all the *.hi and *.o temporary files lying around. You can also simply invoke ghci with the -fbyte-code command line option. If that fails, please complete the paste of your session below with your invocation of ghci. There might be something else going on. Thanks, pepe On Wednesday, September 1, 2010, Steve Severance wrote:

How do I tell? Does this mean that if the exception is occurring in a haskell library I can't get to it? I am trying to run down a Prelude.read: No Parse error and I need to see the value that it is failing to parse on.

Thanks.

Steve

On Tue, Aug 31, 2010 at 11:05 AM, Pepe Iborra wrote:

...

Hi Steve

The debugger only traces calls in interpreted code. Perhaps the call to myMethod is being made from object code?

Admittedly, the ghci debugger can take some effort to learn to use properly. Make sure that you give a look to the ghc user guide if you haven't done so yet.

Best, pepe

On Tuesday, August 31, 2010, Steve wrote:

...

I am trying to debug a problem in GHCI. I invoke my method with trace but when it breaks on exception i can't get this history. Output is below. Thanks.

relude Symbols> :set -fbreak-on-exception Prelude Symbols> :trace myMethod Loading package HUnit-1.2.2.1 ... linking ... done. Loading package syb-0.1.0.2 ... linking ... done. Loading package base-3.0.3.2 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package time-1.1.4 ... linking ... done. Loading package random-1.0.0.2 ... linking ... done. Loading package QuickCheck-1.2.0.0 ... linking ... done. Loading package Decimal-0.1.0 ... linking ... done. Loading package array-0.3.0.0 ... linking ... done. Loading package Diff-0.1.2 ... linking ... done. Loading package bytestring-0.9.1.5 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-time-1.0.0.3 ... linking ... done. Loading package convertible-1.0.9 ... linking ... done. Loading package utf8-string-0.3.4 ... linking ... done. Loading package HDBC-2.2.6 ... linking ... done. Loading package HDBC-mysql-0.6.3 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package network-2.2.1.7 ... linking ... done. Loading package HTTP-4000.0.9 ... linking ... done. Loading package binary-0.5.0.2 ... linking ... done. Loading package digest-0.0.0.8 ... linking ... done. Loading package filepath-1.1.0.3 ... linking ... done. Loading package unix-2.4.0.0 ... linking ... done. Loading package directory-1.0.1.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package zlib-0.5.2.0 ... linking ... done. Loading package zip-archive-0.1.1.6 ... linking ... done. Loading package Core-0.0.1 ... linking ... done. Beginning Update Stopped at <exception thrown> _exception ::  e = GHC.Exception.SomeException (GHC.Exception.D:Exception _

(GHC.Show.D:Show ...) ....)                                  (GHC.IO.Exception.IOError Nothing GHC.IO.Exception.UserError ....) [<exception thrown>] Prelude Symbols> :history Empty history. Perhaps you forgot to use :trace? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- -- José Iborra        http://www.dsic.upv.es/~jiborra -- UPV Valencia       Telf. (+34) 96 387 00 00 (ext) 83529 -- Camino de Vera s/n. 46022 Valencia (Spain)

-- ------------------------------------ Steve Severance c. 240.472.9645 e. steve@medwizard.net ------------------------------------ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- -- José Iborra http://www.dsic.upv.es/~jiborra -- UPV Valencia Telf. (+34) 96 387 00 00 (ext) 83529 -- Camino de Vera s/n. 46022 Valencia (Spain)