[GHC] #3217: Make GHCi have separate flags for interactive Haskell expressions

[GHC]

#3217: Make GHCi have separate flags for interactive Haskell expressions
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  Reporter:  simonpj           |          Owner:                  
      Type:  feature request   |         Status:  new             
  Priority:  normal            |      Milestone:  6.12 branch     
 Component:  Compiler          |        Version:  6.10.2          
  Severity:  normal            |       Keywords:                  
Difficulty:  Unknown           |       Testcase:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
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 It's becoming clear that in GHCi we want to have a separate set of
 command-line flags for
   * Compiling Haskell expressions typed at the GHCi prompt
   * Compiling entire modules, eg via `:load`
 Examples of this need are:
   * We already have an ad-hoc difference in the way that type-class
 defaults are applied:
 http://www.haskell.org/ghc/docs/latest/html/users_guide/interactive-
 evaluation.html#extended-default-rules
   * In #3202 there's a well-argued request to change behaviour of the
 monomorphism restriction

 So the new feature would consist of:
  * The `InteractiveContext` should contain a set of `DynFlags` used for
 compiling command-line Haskell expressions (the ''interactive
 `DynFlags`'')
  * The `:set` command would change both the `DynFlags` maintained by GHCi
 for compiling entire modules (the ''batch `DynFlags`''), and the
 interactive `DynFlags`.
  * A new `:seti` command to change the interactive flags
  * Just possibly a `:setb` command to set the batch flags but leave the
 interactive ones unchanged.

 Arguably it'd be good to have a command to display the current flag
 settings (of either `DynFlags`) but that's another blob of work.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3217>
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