enumFrom errors for Index 0

[kleinreact]

enumFrom and alike should not error for Index 0. They should return the empty list instead.

clashi> enumFrom (undefined :: Index 0)
*** Exception: X: maxBound of 'Index 0' is undefined

[christiaanb]

I think the definition of Enum isn't clear that it should not error in this case, or that it should return the empty list. I agree it would be nice and that we should probably change the implementation to behave accordingly.

[christiaanb]

I mean, it even states https://hackage.haskell.org/package/base-4.20.0.1/docs/Data-Enum.html#v:enumFrom

a possible implementation being enumFrom n = n : enumFrom (succ n)

which would have the following reduction to WHNF:

enumFrom (undefined :: Index 0)
==>
(undefined :: Index 0) : enumFrom (succ (undefined :: Index 0))

[kleinreact]

You are right, there is no requirement that enumFrom should not error in that case, but producing the empty list seems to be the "more correct" solution to me, to be honest. I just recognized this behavior by accident and thought that an error-less solution might be the better option here.

[DigitalBrains1]

I agree that the empty list is the desirable outcome here, even though there are no Haskell laws preventing the current implementation.