Should exhaustiveness testing be on by default?
ndmitchell at gmail.com
Tue May 19 07:01:59 EDT 2009
> > ... exhaustive pattern checking might well help out a lot of
> > people coming from untyped backgrounds...
> Or even people from typed backgrounds. I worship at the altar of
> exhaustiveness checking.
Do you really want exhaustiveness, or is what you actually want safety?
test1 = head 
test2 = x where (x:xs) = 
test3 = (\(x:xs) -> 1) 
test4 = f  where f  = 1
GHC reports that test4 has incomplete patterns, but the others don't.
However, test4 is safe, but the others aren't. Exhaustiveness is a
poor approximation of safety. GHC's exhaustiveness checker is a poor
approximation of exhaustiveness. 2 is a poor approximation of pi :-)
Using Catch, it reports that test1..3 were faulty, but test4 is safe.
More information about the Glasgow-haskell-users