On 10/06/15 14:22, Johan Tibell wrote: > On Wed, Jun 10, 2015 at 12:42 AM, David Luposchainsky > <dluposchain...@googlemail.com <mailto:dluposchain...@googlemail.com>> > wrote: > > I think there are two important consequences of MonadFail. First of > all, we can > all safely write failable patterns if we so desire. Second, the > compiler can > ensure other people's codebases do not lie to us (knowingly or > unknowingly). > > > The second is a bit overstated I think. Any function you call can still > have partial pattern matches in all the other places Haskell allows them > and you wouldn't know from the type.
For most of them, at least you get a warning from GHC (not for patterns inside lambda, sadly, although that should be fixable). But for do Just x <- a ... it's not possible in principle to give a warning, because it's not clear whether the implicit call to fail is intended. Roman
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