[GHC] #12003: Improve error message about closed variables

[GHC]

#12003: Improve error message about closed variables
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        Reporter:                    |                Owner:
  facundo.dominguez                  |
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  StaticPointers
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11656            |  Differential Rev(s):  Phab:D2167
       Wiki Page:                    |
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Changes (by facundo.dominguez):

 * status:  new => patch
 * differential:   => Phab:D2167


@@ -23,1 +23,1 @@
- Where it would be more helpful to get a message like
+ where it would be more helpful to get a message like

New description:

 After allowing local bindings in static definitions the following program
 {{{
 {-# LANGUAGE StaticPointers #-}
 module M where

 f x = static g
   where
     g = h
     h = x
 }}}
 yields the error
 {{{
 ../tmp/M.hs:4:7: error:
     • ‘g’ is used in a static form but it is not closed.
     • In the expression: static g
       In an equation for ‘f’:
           f x
             = static g
             where
                 g = h
                 h = x
 }}}
 where it would be more helpful to get a message like
 {{{
 ../tmp/M.hs:4:7: error:
     • ‘g’ is used in a static form but it is not closed because it
       uses ‘h’ which uses ‘x’ which is not let-bound.
     • In the expression: static g
       In an equation for ‘f’:
           f x
             = static g
             where
                 g = h
                 h = x
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12003#comment:1>
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