> I don't see much gain. It will break previously working code and the
> workaround to the breakage will likely be manually reimplementing enumFromTo
> in each instance.
As an aside, many years ago I did exactly that after being bit by Enum
infelicities, and while you could say it's a reimplementation, in my
opinion it's a better implementation:
-- | Enumerate an inclusive range. Uses multiplication instead of successive
-- addition to avoid loss of precision.
--
-- Also it doesn't require an Enum instance.
range :: (Num a, Ord a) => a -> a -> a -> [a]
range start end step = go 0
where
go i
| step >= 0 && val > end = []
| step < 0 && val < end = []
| otherwise = val : go (i+1)
where val = start + (i*step)
-- | Enumerate a half-open range.
range' :: (Num a, Ord a) => a -> a -> a -> [a]
range' start end step = go 0
where
go i
| step >= 0 && val >= end = []
| step < 0 && val <= end = []
| otherwise = val : go (i+1)
where val = start + (i*step)
-- | Infinite range.
range_ :: (Num a) => a -> a -> [a]
range_ start step = go 0
where go i = start + (i*step) : go (i+1)
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