Hmm, this gives me a new idea for a feature request - how about a function that evaluates to the source code line number it was called from? ;-)
Well, that wouldn't be a function, but one of the other "-hc"s (j? n?) has srcloc_annotate which is a macro that does that. It would be nice if ghc had it. Meanwhile, I use -pgmF to replace certain functions with *_srcloc ones that pass a SrcLoc argument, and it works mostly ok. I don't know what other people do, but having file:line in logs and test failures is pretty handy. Only "mostly" because it replaces things in strings, because I can't use cpp because it doesn't understand dots in identifiers, and can't use Language.Haskell.Parser because it *also* doesn't understand dots in identifiers, so it's Regex.subRegex (speaking of not being designed for qualified import...) until I get around to doing it with parsec.