Common debugging/error/exception functions that give file location information
> $(err "OH NO!")
> main:Main main.hs:16:1 OH NO!
Notice how it displays package:module file:line:character
It exposes the functions err (error), undef (undefined), and trc (Debug.Trace.trace). All of these behave the same as their normal counterpart but also spit out a location.
Here is my favorite helper, debug, which is like trace but just show the value.
> debug [1,2,3]
> DEBUG: [1,2,3]
And The Template Haskell version.
> $(dbg) [1,2,3]
> DEBUG main:Main main.hs:1:3 [1,2,3]
Also there is a version of thrwIO that gives location information
> ($(thrwIO) $ AException) `catch` \e -> putStrLn ("Caught " ++ show (e :: AException))
> Caught AException "main:Main test/main.hs:25:6"
See module for a listing of all the functions with short descriptions, and the homepage for some more examples https://github.com/gregwebs/ErrorLocation.hs