On Tuesday 07 November 2006 17:32, Lennart Augustsson wrote:
On Nov 7, 2006, at 11:47 , apfelmus@quantentunnel.de wrote:
Henning Thielemann wrote:
On Tue, 7 Nov 2006, Simon Marlow wrote:
I'd support fractional and negative fixity. It's a simple change to make, but we also have to adopt
http://hackage.haskell.org/cgi-bin/haskell-prime/trac.cgi/wiki/ FixityResolution
I've added the proposal to the end of that page. In fact, the page already mentioned that we could generalise fixity levels, but it didn't mention fractional or negative values being allowed.
Maybe that page could also mention earlier proposals and the solutions without precedence numbers. I prefer the non-numeric approach with rules like "(<) binds more tightly than (&&)", because it says what is intended and it allows to make things unrelated that are unrelated, e.g. infix operators from different libraries. Consequently a precedence relation to general infix operators like ($) and (.) had be defined in each library.
I think that computable real fixity levels are useful, too. A further step to complex numbers is not advised because those cannot be ordered.
But ordering of the computable reals is not computable. So it could cause the compiler to loop during parsing. :)
-- Lennart
Ha! Well, as long as we're being pedantic, surely we wouldn't need any set larger than the rationals (which does have a decidable ordering)? Also, since I'm commenting anyway, I rather like the idea of specifying operator precedences via a partial order. However, I also feel that there needs to be some work done to make sure there aren't gremlins hiding in the details. Has anyone worked out the theory on this? How does associating to the right vs left play into the picture? How does it fit into the parsing technology? -- Rob Dockins Talk softly and drive a Sherman tank. Laugh hard, it's a long way to the bank. -- TMBG