Re: [Haskell-cafe] Why were unfailable patterns removed and "fail" added to Monad?

On Fri, Jan 20 2012 at 06:22 +0100, Evan Laforge wrote:

On Thu, Jan 19, 2012 at 8:53 PM, Edward Z. Yang wrote:

...

It's not obvious that this should be turned on by -Wall, since you would also trigger errors on uses like:

[ x | Just x <- xs ]

[...] I would have suggested that listcomp match failures yield [] but monad ones be errors, but now that list comps and monads are back together again maybe that's not so easy to do...

Perhaps a generalization of this would be to warn only if fail was inherited by the original Monad typeclass, where it seems obvious that fail takes the role of a ``work-around''. When fail is overwritten one could perhaps assume that calling it is the intended behavior for pattern match failures. Lu