Aha, that's because `:t` operates on expressions, and when a pattern
synonym is used as an expression the required and provided contexts are
merged into one. Makes sense.
/ Emil
Den 2016-05-26 kl. 20:59, skrev Emil Axelsson:
However, it seems that `:t` gives the wrong type:
*Main> :t AddP
Num a, Eq a) => Exp a -> Exp a -> Exp a
Then it's fine
Simon
| -Original Message-
| From: Glasgow-haskell-users [mailto:glasgow-haskell-users-
| boun...@haskell.org] On Behalf Of Emil Axelsson
| Sent: 26 May 2016 16:27
| To: glasgow-haskell-users
| Subject: Pattern s
gow-haskell-users [mailto:glasgow-haskell-users-
| boun...@haskell.org] On Behalf Of Emil Axelsson
| Sent: 26 May 2016 16:27
| To: glasgow-haskell-users
| Subject: Pattern synonyms and GADTs in GHC 8.0.1
|
| I have a problem where a pattern synonym doesn't provide the expected
| type r
I have a problem where a pattern synonym doesn't provide the expected
type refinement in GHC 8.0.1.
{-# LANGUAGE GADTs #-}
{-# LANGUAGE PatternSynonyms #-}
data Exp a
where
Num :: (Eq a, Num a) => a -> Exp a
Add :: (Eq a, Num a) => Exp a -> Exp a -> Exp a
pattern NumP a = Num a
pat
