[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            |   Resolution:                  
    Keywords:                    |   Difficulty:  Unknown         
    Testcase:                    |           Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |  
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Comment (by claus):

 1. Ok. In batch mode, in-source flags/options apply to the current module
 only, not to imports or importers, while commandline flags/options apply
 transitively to the whole session.

  In GHCi, there is currently no equivalent to the former, only to the
 latter.

 Your "interactive flags" that apply to the current session prompt only,
 not to code loaded during the session, would be the equivalent to GHCi
 prompt pragmas, just that you are suggesting a different syntax/interface.

 I agree that offering both prompt and session flags would be more
 consistent. I'm still slightly concerned about the interface, which could
 easily become more confusing rather than simpler.

 2. This was beginning to sound more and more like deja vu (does that even
 apply to sounds?-), and indeed: "Change the meaning of -fextended-default-
 rules" #1877

 3. In current GHC head, what baked-in rules are not switched off by `:set
 -XNoExtendedDefaults`?

 4. While you're dealing with this, could you please remove the current
 inconsistency that in-source flags are not propagated to the interactive
 flags? Given module
 {{{
 {-# LANGUAGE PatternGuards #-}

 f x | () <- x = x
 }}}
 I would expect to have `PatternGuards` available when GHCi is in `*Main`
 (as opposed to `Main`), but that isn't the case:
 {{{
 Ok, modules loaded: Main.
 *Main> let g x | () <- x = x

 <interactive>:1:8:
     Warning: accepting non-standard pattern guards (use -XPatternGuards to
 suppress this message)
                  () <- x
 }}}
 and having to repeat all those pragma flags in the GHCi session is
 somewhat tedious.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3217#comment:3>
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