A common use of "+" is for the operation of an abelian semigroup or monoid (any semigroup can be converted into a monoid anyway).

Alexey.

P.S. I was tempted to suggest "++" for cancellative monoids and "**" for arbitrary monoids, but "++" on lists is not quite cancellative if one of the lists is infinite.

On Saturday, September 12, 2015 at 10:52:01 AM UTC+2, M Farkas-Dyck wrote:

On 11/09/2015, David Thomas <davidle...@gmail.com> wrote:
> a subtraction operation that returns a different type

On 12/09/2015, Alexey Muranov <alexey....@gmail.com> wrote:
> My 2 cents: the difference of two points in an affine space is a vector,
> the sum of a point of an affine space and a vector is another point.

This would mean multi-parametre type classes or type families, so we'd
need to canonicalize them first, which seems unlikely in near future
at least.