Re: [q-lang-users] New stuff in cvs: multichar ops, views

[Albert G. <Dr....@t-...>]

Sorry for chiming in so late, I'm still trying to catch up on my email.

Rob Hubbard wrote:
> Upon a little further thought, I would want only (+:) to be available
> for pattern matching. If the presence of a (-:) operator would upset
> the pattern matching, then I'd withdraw the suggestion in any case...

Unfortunately, with the current Wadler view system, you can't define
alternative views like that. I.e., if you define a view which returns
X+:Y and X-:Y for the two half-planes, then you'll also have to write
rules matching against both. That's why I didn't include '-:' in the
first place, in fact I had the same idea a while back. ;-)

For more elaborate kinds of views, so-called value input would be needed
which would allow you to pick a certain variation of a view in the lhs
pattern. One such proposal can be found on the Haskell site. Also, a
while back LtU mentioned an ICFP07 submission from the Microsoft FP
team, which also discusses a generalized view mechanism (for F#, IIRC).
I still have to take a closer look at that. I know that some of you guys
are on this list, maybe you could comment on that? :)

Considering the precedence of '+:' a.k.a. ':+', I can see that it would
be convenient to have a higher priority for some uses, but wouldn't that
confuse Haskell programmers where ':+' has the same precedence as '+'?
After all the current representation was meant to be more or less
compatible with Haskell.

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag