Avoid accidental flooring when converting `Time unit` to numeric types

[dcastro]

I found it unexpected that toNum floors the number before converting it to Num a. This is neither documented nor (IMO) something most users would expect to happen.

toNum @Second @Double (sec 1.4)
1.0
toNum @Second @Rational (sec 1.4)
1 % 1

This can lead to surprising results:

λ> toUnit @Second $ ms 999
999/1000s
λ> toNum @Second @Rational $ toUnit @Second $ ms 999
0 % 1

AFAICT, there is no way to convert Time unit to an arbitrary Num a => a without flooring the ratio first.

So, I propose we deprecate toNum (and eventually delete it) and split it into floorRat (which already exists) and toFractional:

• add toFractional to support properly converting to Double, Float, etc:
  1. We could losslessly convert Time unit -> Ratio Natural -> Ratio Integer
  2. and then use fromRational :: Fractional a => Ratio Integer -> a
• to convert to integral types, we already have floorRat:
  • floorRat has the right constraint to prevent surprises like the ones I described above (Integral instead of Num) and a name that better describes what it does.

[dcastro]

Re-opening this issue.

We've deprecated toNum in v1.3.0. Let's delete it in the next release.