Re: Storable instance of () is broken

Am Mi., 5. Jan. 2022 um 12:42 Uhr schrieb David Feuer

:

No. Consider a type like this:

data Foo a = Foo !Int !a

instance Storable a => Storable (Foo a) where ...

Now if a happens to be (), we pay only one word per Foo. [...]

This is exactly the kind of breakage I had in mind: With the proposed change, the storage layout would change, and the compiler wouldn't warn you about that at all. Note that I'm not arguing about memory efficiency, it's all about a subtle semantic change for the sake of a single library, wanting to change something which was in place for 10-20 years. Seems like an extremely bad move from the POV of the Haskell ecosystem: It's exactly this kind of ad hoc changes which annoys people.