Should exhaustiveness testing be on by default?
lennart at augustsson.net
Tue May 19 07:18:08 EDT 2009
Excellent, is there a -fuse-catch flag for ghc? :)
On Tue, May 19, 2009 at 12:01 PM, Neil Mitchell <ndmitchell at gmail.com> wrote:
>> > ... 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?
> With -fwarn-incomplete-patterns:
> 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.
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