Negation

[Cale Gibbard]

> But I agree they should all be legal, i.e. that unary minus should bind
> more tightly than any infix operator (as in C).

I'd just like to interject that I disagree, and think that the current
behaviour is about as good as one could hope for. Negation is an
additive operation, and thus has lower precedence than multiplication
and exponentiation.

-x^2 must be interpreted as -(x^2), not as (-x)^2.

Similarly, though it seems to confuse some people, it makes more sense
that  - x `mod` y  is parsed as  - (x `mod` y)  since mod has to do
with multiplication, so it should bind more tightly than additive
operations.

 - Cale