[GHC] #11941: stage restriction mentioned when an identifier is out of scope

15 Apr 2016

      #11941: stage restriction mentioned when an identifier is out of scope
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           Reporter:  aavogt         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1-rc2
           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:
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 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 import Data.Monoid

 const (return []) $ mempty { getFrst = Just () }
 }}}

 {{{
 typeErrBug.hs:5:21: error:
     • GHC stage restriction:
         ‘getFrst’ is used in a top-level splice, quasi-quote, or
 annotation,
         and must be imported, not defined locally
     • In the second argument of ‘($)’, namely
         ‘mempty {getFrst = Just ()}’
       In the expression: const (return []) $ mempty {getFrst = Just ()}

 typeErrBug.hs:5:30: error:
     Not in scope: ‘getFrst’
     Perhaps you meant one of these:
       ‘getFirst’ (imported from Data.Monoid),
       ‘getLast’ (imported from Data.Monoid)
 }}}

 The stage restriction error shouldn't be mentioned: `getFrst` isn't
 defined at all while the "not defined locally" phrase says it's defined
 (in the wrong spot).

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11941
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