[GHC] #12693: Relax qualified import syntax

12 Oct 2016

      #12693: Relax qualified import syntax
-------------------------------------+-------------------------------------
           Reporter:  cblp           |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
  (Parser)                           |
           Keywords:  import,        |  Operating System:  Unknown/Multiple
  qualified, syntax                  |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  10478
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 = Problem =

 Case 1.
 {{{#!hs
 import Data.HashMap (HashMap)
 import qualified Data.HashMap as HashMap
 import Data.Map (Map)
 import qualified Data.Map as Map
 import Data.Set (Set)
 import qualified Data.Set as Set
 import Data.Text (Text)
 import qualified Data.Text as Text
 }}}

 Module names start in different columns, so the user cannot search it
 without help of tools, so the code is unreadable.

 Case 2.
 {{{#!hs
 import           Data.HashMap (HashMap)
 import qualified Data.HashMap as HashMap
 import           Data.Map (Map)
 import qualified Data.Map as Map
 import           Data.Set (Set)
 import qualified Data.Set as Set
 import           Data.Text (Text)
 import qualified Data.Text as Text
 }}}

 Too many space used, too less space left for imported items list, too hard
 to maintain without special tools.

 = Proposal =

 Allow to write `qualified` keyword after module name:

 {{{#!hs
 import Data.HashMap (HashMap)
 import Data.HashMap qualified as HashMap
 import Data.Map (Map)
 import Data.Map qualified as Map
 import Data.Set (Set)
 import Data.Set qualified as Set
 import Data.Text (Text)
 import Data.Text qualified as Text
 }}}

 All the problems solved!

 This proposal looks a little like ShorterImportSyntax and #10478, but
 differs from them in such ways:
 1. It doesn't actually make imports shorter in visible symbols, only in
 lines used (in case of very long imported items list), a little.
 2. It doesn't introduce new syntax constructions looking like existing but
 doing other things.
 3. It is easy to implement and understand.
 4. It looks more natural from the point of view of English language.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12693
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