[Haskell-cafe] Where does ~> come from?

[Steve Lihn]

If ~> does not have any special meaning and it could be ### or xyz,
then how does GHC know to print
 a ~> b, but not ~> a b
 a ### b, but not ### a b
 xyz a b, but not a `xyz` b

Simply because xyz is alphanumeric?


On Wed, Feb 20, 2008 at 12:34 AM, David Menendez <dave at zednenem.com> wrote:
> On Feb 19, 2008 4:15 PM, Wolfgang Jeltsch <g9ks157k at acme.softbase.org> wrote:
> > Am Dienstag, 19. Februar 2008 18:26 schrieben Sie:
> > > […]
> >
> > > However, I was told this:  ~> a b is a ~> b, but if I write c a b and
> > > wish the effect of a `c` b. This would not work. ~> as an infix operator
> > > has a special place in GHC. It is not "just a type variable".
> >
> > Sorry, but I don't understand fully what you mean. :-(  But nevertheless,
> > a ~> b is not the same as ~> a b but as (~>) a b.  It's just like with
> > ordinary operators where a + b is the same as (+) a b.
>
> Note that some (all?) versions of GHC will incorrectly print "a ~> b"
> as "~> a b".
>
> <http://hackage.haskell.org/trac/ghc/ticket/1930>
>
> Prelude> :t undefined :: a + b
> undefined :: a + b :: forall (+ :: * -> * -> *) a b. + a b
>
> It mostly gets infix type constructors right, although there are
> apparently problems with precedence and associativity.
>
> --
> Dave Menendez <dave at zednenem.com>
> <http://www.eyrie.org/~zednenem/>
>
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