Should exhaustiveness testing be on by default?

[Neil Mitchell]

> Excellent, is there a -fuse-catch flag for ghc? :)

No, but there is for Yhc. If you write to the Haskell standard (minus
a little bit), don't like libraries and can get Yhc to compile (good
luck!) then it's just a few command lines away.

If GHC (or GHC + some scripts) could produce a single Core file
representing a whole program, including all necessary libraries, then
implementing Catch would be a weekends work.

Thanks

Neil

>
> 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.
>>
>> Thanks
>>
>> Neil
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>