Incorrect assumptions from BoundedEnum laws.

[MaloJaffre]

These instances / functions all require that fromEnum bottom == 0 to work properly, although there is no law to enforce this:

• BoundedEnum (Maybe a)
• BoundedEnum (Either a b)
• BoundedEnum (Tuple a b)
• defaultToEnum
• defaultFromEnum
• toEnumWithDefaults

Two ways to fix this:

• Add fromEnum bottom == 0 law, this is commonly true, but e. g. not in purescript-dom

• Rework these instances / functions to work in these edges cases, adding / substracting fromEnum bottom in fromEnum / toEnum respectively.

Unfortunately these are IMO breaking changes.

[garyb]

Did you see #23? It's been a while since I looked at that discussion, but I think it covers similar territory.

[MaloJaffre]

#23 is more about laws of pred and succ in BoundedEnum context while this is about what values are allowed for fromEnum bottom (currently any number, while only 0 work for some instances / functions)

[garyb]

This will be somewhat resolved in the release for the 0.12 compiler - I've removed the offending instances for now (they are possible, but they're going to be kinda gnarly and probably slow), and added notes to the functions that make assumptions that fromEnum bottom = 0.

Thanks!