On Sun, Nov 6, 2011 at 4:46 PM, Duncan Coutts
Ultimately no code breaks, after all it is changing the associativity of an operator that is by definition *associative*. ;)
That's what I thought too, but I already gave an example:
a <> empty <+> b
This means different things depending on whether we use infixl or infixr. And as I noted, this doesn't bite Text.PrettyPrint.Leijen because it lacks the <+> unit law.
Bah. Good point.
So my tentative suggestion is:
infixr 6 <> infixr 5 <+> infixr 4 $$, $+$
So <> binds tighter than <+> and $$ and $+$ are still lower precedence than <> and <+>, but switched round to being right associative.
Reasonable, but there is the caveat that causes another problem, which is that now <+>, : and ++ conflict, which was why we had to raise <> to 6 in the first place. We could adopt your proposed fix one level up though with: infixr 7 <> infixr 6 <+> -Edward