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

Malcolm Wallace Malcolm.Wallace at cs.york.ac.uk
Tue Sep 20 11:00:14 EDT 2005

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
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.


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