[Haskell-cafe] How to locate a <<loop>>?

[Malcolm Wallace]

Jørgen Hermanrud Fjeld <jhf at hex.no> writes:

> I have a generated Haskell program that emits a 
> "Fail: <<loop>>"
> at runtime. 
> Are there some tools or standard manner for identifying the lines that
> participate in the loop? 

Provided your program does not use too many GHC extensions or fancy
libraries, you could try using the Hat tracer
    http://haskell.org/hat
which now comes with two tools called 'hat-nonterm' and 'black-hat',
specially designed for finding the cycle that leads to a black hole
or non-termination.

Regards,
    Malcolm