David Roundy wrote:
Any ideas for tricks to see where a program is looping indefinitely? I'm sure I can track down this bug pretty easily, but is seems like this is something one really ought to be able to do...
May I answer your question by advertising the Haskell tracer Hat? http://www.cs.york.ac.uk/fp/hat/ The various trace viewing tools of Hat show you your computation in various ways and thus help you in particular to locate a fault. In your case hat-trail is the right tool. Just start hat-trail with the trace of your looping computation (you may interrupt the computation early to save time and trace space; but note that a traced computation is considerably slower). Then repeatedly press "enter" to see the whole virtual stack. Each stack entry shows a function with its arguments in most evaluated form. I should point out that Hat works for Haskell 98; it supports only few libraries and no ghc language extensions. Real soon we will release a new version supporting more libraries, a few language extensions (multiparameter classes, functional dependencies) and some other improvements. Ciao, Olaf -- OLAF CHITIL, Dept. of Computer Science, The University of York, York YO10 5DD, UK. URL: http://www.cs.york.ac.uk/~olaf/ Tel: +44 1904 434756; Fax: +44 1904 432767