Debugging cabal-install and Cabal with ghci 6.7

[Simon Marlow]

Pepe Iborra wrote:

>> The current behaviour is to break when any exception is raised.  
>> Perhaps we want it to only break when an exception reaches the 
>> outermost level?  Or have a separate option to do that?
>>
> 
> Oh, I see. This is a bit counterintuitive for me. My take would be to 
> break only when an error condition is reached, which includes an 
> uncaught exception.
> fbreak-on-error would be a good name for a flag doing this, which could 
> possibly be enabled by default?

An uncaught exception is always just printed in GHCi, so there wouldn't be much 
benefit in having it trigger a breakpoint.  A better idea I think would be to 
make :history/:back still work after an evaluation has completed (with an 
exception or just normally).  I'll add this to the list.

> This would require that a tag is stored in the tick structure indicating 
> the breakpoint site type (fn application, binding introduction, do 
> statement, etc.). Then the tag can be used to filter the breaks that are 
> stored. It should be cheap, and I believe that the Tolmach ML debugger 
> did this already, and so does the ocaml debugger. I don't know if 
> perhaps we are doing this already?

we're not doing it, but we could.

Cheers,
	Simon