[ interpolate ] Implement Interpolation for primitive numeric types

[buzden]

Description

Interfaces Interpolation and Show have different meanings, and polymorphic implementations of Interpolation tend to require Interpolation for inner types rathen than Show, which is logical. Primitive numeric types have almost single meaningful canonical string representation, so I suggest to add Interpolation implementaitons for them (and for Nat too).

Should this change go in the CHANGELOG?

• If this is a fix, user-facing change, a compiler change, or a new paper
  implementation, I have updated CHANGELOG.md (and potentially also
  CONTRIBUTORS.md).

[stefan-hoeck]

Personally, I don't think this is a good idea. I'm not opposed to adding default implementations for Interpolation, but in my opinion, they should not be auto-imported via the Prelude. There are quite a few use cases, where custom implementations would be useful (displaying numbers in a different base or adding separators for readability), and those use cases will now require newtype wrappers or explicit function calling to still work correctly.

I'd prefer it, if these default implementations would go into a module in base, that needs to be imported explicitely.

[buzden]

Well, that sounds reasonable, let's move it to base. At least, this change indeed will be backwards compatible with custom user declarations