For expressions operator sections will also be difficult to deal with, i.e. the expression (!x) could either be a parenthesized prefix !, or a section for binary !. Some disambiguation mechanism would be required. Currently such disambiguation is hardcoded for - as a special case in the grammar. Atze On 8 Jul, 2010, at 09:09 , Simon Peyton-Jones wrote:
Yes, I somewhat hacked up the rules for ! in an ad-hoc way. I really wanted to allow
f !x !y = (x,y)
which meant a bit of fiddling, because LHSs are parsed as terms, so this is parsed as
(f ! x) ! y
(ie as infix operators) and I have to squizzle around to re-interpret them as prefix operators. Not very cool. Something unified would be a Good Thing.
Simon
| -----Original Message----- | From: haskell-prime-bounces@haskell.org [mailto:haskell-prime- | bounces@haskell.org] On Behalf Of John Meacham | Sent: 08 July 2010 00:59 | To: haskell-prime@haskell.org | Subject: prefix operators | | It occurred to me the other day that Haskell (w/ bang patterns) now has | 3 prefix operators, all of which are defined independently and follow | their own special rules for parsing. we have (-), (!) and (~). | | It would seem to me that we should somehow be able to unify the | mechanism behind parsing these, as in practice, it seems that prefix | operators are useful in haskell. | | We have some similarities, - and ! are both infix and prefix operators, | ~ is not. ! and ~ can only be in patterns as prefix, (-) can be in both | patterns and expressions. | | But it seems like we may be able to come up with a common way of parsing | them all, prolog has had user defined infix, prefix, and postfix | operators (sharing the same name even) and is still able to parse things | properly so I don't think there will be a technical issue. | | My first impulse is to treat application as just another binary operator | with a certain precedence and find appropriate precedences for !,~,- in | the new framework. | | note: I am not proposing user defined prefix operators, just musing | about whether we can unify the rules behind parsing the current three | prefix operators, perhaps folding them into the fixity resolution | algorithm. | | John | | -- | John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ | _______________________________________________ | Haskell-prime mailing list | Haskell-prime@haskell.org | http://www.haskell.org/mailman/listinfo/haskell-prime
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- Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze . /--| \ Fax : +31-30-2513971 .... | Email: atze@cs.uu.nl ............ / |___\