The topic of improving exception diagnosis in Haskell is hot at the moment, and I'm pleased to announce the release of LocH, a small Haskell module providing source location-specific error messages and debugging strings for Haskell code. It uses the compiler-expanded 'assert' token, rather than cpp or m4, to provide a lightweight approach to generating source locations. No preprocessor is required. The code is available under a BSD license. The LocH home: http://www.cse.unsw.edu.au/~dons/loch.html The API: http://www.cse.unsw.edu.au/~dons/loch/Debug-Trace-Location.html Example usage: import Debug.Trace.Location main = trace assert "Starting ..." $ do print 1 trace assert "Finished" $ do print 2 let x = check assert $ head ([] :: [Int]) print x Will produce: $ ./a.out A.hs:4:10-15: Starting ... 1 A.hs:6:10-15: Finished 2 a.out: A.hs:8:18-23: Prelude.head: empty list LocH provides located versions of trace, failure, as well as check and checkIO to wrap exception-throwing pure and IO code. May all your exceptions be located, Don