GHC 6.8.1 RC debugger only breaking on first evaluation of a function

Tomasz Zielonka tomasz.zielonka at
Wed Sep 19 04:05:12 EDT 2007

On Tue, Sep 18, 2007 at 02:26:38PM -0400, Olivier Boudry wrote:
> Hi all,
> I just tried the new GHCi debugger. A great new feature of GHCi 6.8.1.
> When debugging a function, as for example the qsort function given as an
> example in the "3.5 The GHCi Debugger" documentation page, the debugger will
> only break on first function evaluation.
> As haskell is pure and lazy it's probably a normal behavior (reuse last
> result instead of recompute) but it's not very practical in a debugger. I
> tried to reload (:r) but it doesn't seems to help. Is there a way to force
> the function to be re-evalutated without quitting, starting, loading prog
> and setting breakpoints again, other than making the function part of the IO
> monad. ;-)

If you don't find a better solution, then at least you can make it
easier to perform the above sequence:

$ cat ~/.ghci
:def . readFile
$ cat script
:l Module
:b 236
$ ghci
GHCi, version 6.8.20070912:  :? for help
Loading package base ... linking ... done.
Prelude> :. script
[1 of 1] Compiling Module           ( Module.hs, interpreted )
Ok, modules loaded: Module.
Breakpoint 0 activated at Module.hs:236:20-45
*Module> _

It should be quite easy to go a step further and generate breakpoint
locations from markers in comments in the source file.

Best regards

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