[Haskell-cafe] ghci breakpoints

Jose Iborra pepeiborra at gmail.com
Sun Nov 29 10:46:31 EST 2009

Hi Sean,

it looks like your Focus module is not interpreted and thus has no breakpoints.
(that error message could be easily improved to let you know this)

The ghci debugger only works with interpreted code, you can either delete all the
*.hi and *.o temporary files or simply use the flag -fbyte-code to ensure that
ghci loads the code in interpreted mode.

By the way, the ghci debugger has a few quirks more.
You probably want to give a read to the debugger docs in the GHC manual if you
plan to use it for anything non trivial.


On 29/11/2009, at 06:18, Sean McLaughlin wrote:

> Hello,
>  I'm having trouble setting breakpoints from ghci.  I load the files
> and I can tell things are working correctly because I can run the
> program and list the locations where I want to set breakpoints.  E.g.
> Prelude> :list Focus.focus
> 510  > focus :: forall s m. Class s m => Neg -> m [Foci]
> 511  > focus f =
> 512  >   let ats = Path.atoms f
> But when I try to set a breakpoint I get
> Prelude> :break Focus.focus
> No breakpoints found at that location.
> Does anyone have ideas about what I'm doing wrong in this case?  Do I
> need to load with some special options to have breakpoints work?
> Thanks,
> Sean
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