id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
4466	Add extension for type application	igloo		"
In
http://www.haskell.org/pipermail/libraries/2010-October/014761.html
we discussed adding an extension for explicit type application.

The main stumbling block is syntax.

For example, we would like to be able to write something to the effect of
{{{
(Just @ Char) 'a'
}}}
and also to be able to pattern match types, e.g.
{{{
f ((Just @ t) x) = (Right @ String @ t) x
}}}

For a more useful example:
{{{
data T where
    MkT :: forall a. a -> (a -> Int) -> T

f (MkT @ a x g) = g (x::a)
}}}

Possible suggested syntaxes to make something of type
{{{
Maybe (forall a. a->a)
}}}
were:
{{{
Just @ (forall a. a->a) id    (@ has another meaning in patterns)
Just[forall a. a->a] id       (pvs, opal, HasCASL with paramterized modules; conflicts with Haskell list syntax)
Just {forall a. a->a} id      (Agda)
#Just (forall a. a->a) id
@Just (forall a. a->a) id     (coq)
}}}

In the last 2 cases we would presumably have something like
{{{
Just :: forall a . a -> Maybe a
Just :: Char -> Maybe Char
#Just :: /\ a . a -> Maybe a
#Just Char :: Char -> Maybe Char
}}}
and similarly
{{{
#map :: /\ a b . (a -> b) -> [a] -> [b]
}}}
"	feature request	new	low	7.6.2	Compiler	6.12.3			wren@… sweirich@… mail@…	Unknown/Multiple	Unknown/Multiple	None/Unknown