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
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