[GHC] #12649: Allow TypeApplications syntax to be used to instantiate type variables in SPECIALISE pragmas

[GHC]

#12649: Allow TypeApplications syntax to be used to instantiate type variables in
SPECIALISE pragmas
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Currently the `SPECIALISE` pragma requires that the user repeat the entire
 type of a binding to instantiate its types. This is often needlessly
 verbose and quite tiresome. Instead, why not allow the user to write the
 desired type as an application with `TypeApplications`?

 For instance, currently we might write,
 {{{#!hs
 foldWithOptionsAndParser :: forall m params. ( MonadIO m, MonadMask m,
 ToRow params )
                          => FoldOptions
                          -> RowParser row
                          -> Connection
                          -> Query
                          -> params
                          -> a
                          -> (a -> row -> m a)
                          -> m a
 foldWithOptionsAndParser opts parser conn template qs a f = ...
 {-# SPECIALISE
     foldWithOptionsAndParser :: FoldOptions -> RowParser row -> Connection
 -> Query -> params -> a
                              -> (a -> row -> IO a) -> IO a #-}
 }}}

 Instead we might want to write,
 {{{#!hs
 {-# SPECIALISE foldWithOptionsAndParser @IO #-}
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12649>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler