[GHC] #11547: Accessing shadowed definitions in GHCi

6 Feb 2016


      #11547: Accessing shadowed definitions in GHCi
-------------------------------------+-------------------------------------
           Reporter:  mniip          |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.0.1-rc1
           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:
-------------------------------------+-------------------------------------
 Apparently GHCi creates a qualified namespace for each line it interprets,
 as can be observed with:
 {{{#!hs
...
data A = A
data A = B
:t A
 A :: Ghci3.A
 }}}
 Apparently accessing shadowed definitions in this way sometimes breaks
 GHCi:
 {{{#!hs
let a = a
let a = a
:t Ghci7.a
<interactive>:1:1: error:
     • GHC internal error: ‘Ghci7.a’ is not in scope during type checking,
 but it passed the renamer
       tcl_env of environment: []
     • In the expression: Ghci7.a
 }}}

 More specifically, complete reproduction instructions:
 {{{#!hs
 GHCi, version 8.1.20160205: http://www.haskell.org/ghc/  :? for help
...
let foo = foo
:t Ghci1.foo
 Ghci1.foo :: t
let foo = foo
:t Ghci1.foo
<interactive>:1:1: error:
     • GHC internal error: ‘Ghci1.foo’ is not in scope during type
 checking, but it passed the renamer
       tcl_env of environment: []
     • In the expression: Ghci1.foo
 }}}

 7.10.2 (and 7.8.3 as verified over IRC by monochrom) appears to have a
 slightly different behavior. It seems it only creates namespaces for
 data/newtype/class declarations. Yet still, it fails with an error the
 first time but works completely fine thereafter:
 {{{#!hs
...
data A = A
data A = A
:t Ghci1.A
 Failed to load interface for ‘Ghci1’
 no package key matching ‘interactive’ was found
:t Ghci1.A
 Ghci1.A :: Ghci1.A
 }}}
7.6.3 uses a different approach to displaying out of scope names so the
 behavior doesn't apply:
 {{{#!hs
...
data A = A
data A = B
:t A
 A :: main::Interactive.A
 }}}
--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11547
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