For the first time I've encountered an infinite loop in a Haskell program I'm writing. I've narrowed it down to a quite specific section of code, but I cannot seem to pinpoint exactly where I have a non-terminating recursive definition. I'm vaguely familiar with :trace and :history in GHCi, but the problem is that some branches of my code involve quite a bit of recursive modifications of a Data.Map.Map in the sense that the map x is obtained by adjusting something in the map x' based on values in another map depending on x'. The specifics don't matter here, but as you can probably tell, if this happens in an intertwined recursive way, my call history gets completely bogged down in all the various comparisons involved in map lookups, adjustments and insertions.
Can anyone recommend a more efficient way to locate infinite loops? It would, for example, help a lot to restrict the call history to calls from a single source file.
Be sure you've used the GHCi debugger to it's full extent, including setting -fbreak-on-exception (useful if you're getting <<loop>>, are you?) and be sure you've tried Stephen's advice of using GHC's warnings.
If these fail (GHCi debugger really shouldn't 'fail', it's just a matter of interpreting the data) then try to run HPC on the looping case so you can visually see branches and values that aren't being evaluated, if it's looping then something that should be getting done probably isn't even being evaluated and that will show up in the marked up HTML.