+1. Making ":" the signal for type variables would break even more code, f.e. fclabels.
"~" almost means "variable", so I'd like that as a prefix. Sjoerd On Sep 15, 2012, at 2:09 AM, Cale Gibbard <[email protected]> wrote: > There's a fair amount of code out there which uses (~>) as a type > variable (we have ~10k lines of heavy arrow code at iPwn). It would be > *really* nice if that could be accommodated somehow. But the proposal > you just gave at least would allow for a textual substitution, so not > quite so bad as having to change everything to prefix notation. > > On 14 September 2012 19:26, Simon Peyton-Jones <[email protected]> wrote: >> Fair point. So you are saying it’d be ok to say >> >> >> >> data T (.->) = MkT (Int .-> Int) >> >> >> >> where (.+) is a type variable? Leaving ordinary (+) available for type >> constructors. >> >> >> >> If we are inverting the convention I wonder whether we might invert it >> completely and use “:” as the “I’m different” herald as we do for >> *constructor* operators in terms. Thus >> >> >> >> data T (:->) = MkT (Int :-> Int) >> >> >> >> That seems symmetrical, and perhaps nicer than having a new notation. >> >> >> >> In terms In types >> >> ----------------------------------------------------------------------- >> >> a Term variable Type variable >> >> A Data constructor Type constructor >> >> + Term variable operator Type constructor operator >> >> :+ Data constructor operator Type variable operator >> >> >> >> Any other opinions? >> >> >> >> Simon >> >> >> >> From: [email protected] [mailto:[email protected]] On Behalf Of >> Conal Elliott >> Sent: 06 September 2012 23:59 >> To: Simon Peyton-Jones >> Cc: GHC users >> Subject: Re: Type operators in GHC >> >> >> >> Oh dear. I'm very sorry to have missed this discussion back in January. I'd >> be awfully sad to lose pretty infix notation for type variables of kind * -> >> * -> *. I use them extensively in my libraries and projects, and pretty >> notation matters. >> >> I'd be okay switching to some convention other than lack of leading ':' for >> signaling that a symbol is a type variable rather than constructor, e.g., >> the *presence* of a leading character such as '.'. >> >> Given the increasing use of arrow-ish techniques and of type-level >> programming, I would not classify the up-to-7.4 behavior as a "foolish >> consistency", especially going forward. >> >> -- Conal >> >> On Wed, Jan 18, 2012 at 6:27 AM, Simon Peyton-Jones <[email protected]> >> wrote: >> >> Dear GHC users >> >> As part of beefing up the kind system, we plan to implement the "Type >> operators" proposal for Haskell Prime >> http://hackage.haskell.org/trac/haskell-prime/wiki/InfixTypeConstructors >> >> GHC has had type operators for some kind, so you can say >> data a :+: b = Left a | Right b >> but you can only do that for operators which start with ":". >> >> As part of the above wiki page you can see the proposal to broaden this to >> ALL operators, allowing >> data a + b = Left a | Right b >> >> Although this technically inconsistent the value page (as the wiki page >> discussed), I think the payoff is huge. (And "A foolish consistency is the >> hobgoblin of little minds", Emerson) >> >> >> This email is (a) to highlight the plan, and (b) to ask about flags. Our >> preferred approach is to *change* what -XTypeOperators does, to allow type >> operators that do not start with :. But that will mean that *some* >> (strange) programs will stop working. The only example I have seen in tc192 >> of GHC's test suite >> {-# LANGUAGE TypeOperators #-} >> comp :: Arrow (~>) => (b~>c, c~>d)~>(b~>d) >> comp = arr (uncurry (>>>)) >> >> Written more conventionally, the signature would look like >> comp :: Arrow arr => arr (arr b c, arr c d) (arr b d) >> comp = arr (uncurry (>>>)) >> or, in infix notation >> {-# LANGUAGE TypeOperators #-} >> comp :: Arrow arr => (b `arr` c, c `arr` d) `arr` (b `arr` d) >> comp = arr (uncurry (>>>)) >> >> But tc192 as it stands would become ILLEGAL, because (~>) would be a type >> *constructor* rather than (as now) a type *variable*. Of course it's easily >> fixed, as above, but still a breakage is a breakage. >> >> It would be possible to have two flags, so as to get >> - Haskell 98 behaviour >> - Current TypeOperator behaviuor >> - New TypeOperator behaviour >> but it turns out to be Quite Tiresome to do so, and I would much rather not. >> Can you live with that? >> >> >> http://chrisdone.com/posts/2010-10-07-haskelldb-and-typeoperator-madness.html >> >> >> _______________________________________________ >> Glasgow-haskell-users mailing list >> [email protected] >> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users >> >> >> >> >> _______________________________________________ >> Glasgow-haskell-users mailing list >> [email protected] >> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users >> > > _______________________________________________ > Glasgow-haskell-users mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users -- Sjoerd Visscher https://github.com/sjoerdvisscher/blog _______________________________________________ Glasgow-haskell-users mailing list [email protected] http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
