Re: the impossible happened

bulatz:
> also it will be cool to have ability to add such annotations to my own
> functions, smthg like:
> 
> head (x:xs) = x
> head [] = superError "head []"
> 
> which will print: "Error: head [] in Module.hs:155"

You can do this already with GHC.Base.assert (almost):

> import GHC.Base (assert)
> 
> f [] = assert False ()
> f x  = ()

*Main> f [1,2]
()
*Main> f []   
*** Exception: t.hs:3:7-12: Assertion failed

At least you can get the line number.

-- Don