Thanks, that makes sense.
And the existing behaviour is in the compiler, so the surrounding parens
are optional and can/should be stripped (except for Api Annotations)
Alan
On Mon, May 18, 2015 at 10:11 AM, Roman Cheplyaka
On 18/05/15 10:57, Alan & Kim Zimmerman wrote:
Hi all
I am working on D836 and have the following test case
data MaybeDefault v where SetTo4 :: forall v a. (( Eq v, Show v ) => v -> MaybeDefault v -> a -> MaybeDefault [a])
GHC 7.10.1 regards the return type of SetTo4 as `MaybeDefault [a]`
The question is, due to the parens, is the return type not the whole RHS?
i.e. Similar to how in the signature
map :: (a -> b) -> [a] -> [b]
the first paramater is a single function.
I am sure I am just confused here.
This is the wrong analogy, since (a -> b) in map's type is in the negative position.
The correct analogy would be the return type of
map :: (a -> b) -> ([a] -> [b])
You could argue it both ways. (But only one of them leads to the above declaration being correct, since the function type is not an instance of MaybeDefault.)
Roman