[GHC] #4832: Inconsistent import of instances in GHCi

[GHC]

#4832: Inconsistent import of instances in GHCi
---------------------------------+------------------------------------------
    Reporter:  sebf              |       Owner:              
        Type:  bug               |      Status:  new         
    Priority:  normal            |   Component:  GHCi        
     Version:  7.0.1             |    Keywords:              
    Testcase:                    |   Blockedby:              
          Os:  Unknown/Multiple  |    Blocking:              
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
---------------------------------+------------------------------------------
 Issuing `import M` in GHCi does not bring the same instances into scope as
 issuing `:m + M` and loading a file that contains `import M` do.

 For example, the module `Control.Applicative` imports
 `Control.Monad.Instances` which defines a `Functor` instance for `((->)
 r)`. The following GHCi session demonstrates that this instance is not in
 scope after issuing an `import` command in GHCi but it is in scope after
 issuing an `:m +` command. It is also in scope after loading a file that
 imports `Control.Applicative`.

 {{{
 Prelude> fmap id id ()

 <interactive>:1:1:
     No instance for (Functor ((->) ()))
       arising from a use of `fmap'
     Possible fix: add an instance declaration for (Functor ((->) ()))
     In the expression: fmap id id ()
     In an equation for `it': it = fmap id id ()
 Prelude> import Control.Applicative
 Prelude Control.Applicative> fmap id id ()

 <interactive>:1:1:
     No instance for (Functor ((->) ()))
       arising from a use of `fmap'
     Possible fix: add an instance declaration for (Functor ((->) ()))
     In the expression: fmap id id ()
     In an equation for `it': it = fmap id id ()
 Prelude Control.Applicative> :m + Control.Applicative
 Prelude Control.Applicative> fmap id id ()
 ()
 }}}

 I expected that issuing an `import` command in GHCi has the same effect as
 issuing an `:m +` command or loading a file with an `import` statement.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4832>
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