[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):

 > Can you precisely define "compatibility"?  Can you imagine implementing
 (or even describing) it in a simple way?

 Sure - the same way it is defined currently, in a single file!-) Actually,
 defining and implementing this would be good in any case, as there
 currently are a few oddities..:

  - no multiple `default` permitted (as in a single file; this could be
 relaxed to permitting *identical* `default`s)

  - no `{-# LANGUAGE X, NoX #-}` (actually, that is currently permitted,
 but I consider it an oversight/bug..)

  - no `{-# OPTIONS_GHC -fthis, -fno-this #-}` (again, that is currently
 permitted..)

 If there are any non-obvious cases, simply require that all modules must
 have the same, identical options for those. In general, proceed as if all
 `*`-ed modules were in a single file, with allowances for identical
 duplicates.

 My intention here is that explicit settings have priority over implicit
 ones (if one module doesn't have an explicit `default`, another does, then
 the combination has the explicitly given `default`). This merging of
 explicit settings might lead to a module not being loadable with the
 merged settings, but this isn't different from that module depending on
 specific settings, which should be made explicit.

 An alternative would be to require identical settings in all modules to be
 loaded in a `*` combination. This would be easier to check, but almost as
 cumbersome as permitting only a single `*`-ed module.

 > If this is really a necessary feature, can you describe a compelling use
 case?  One that doesn't have an easy workaround?

 As I mentioned, a single `*`-ed module would seem to work for me. It is
 just that I've often been annoyed if people who couldn't imagine a use
 case decided that there were no use cases, so I didn't want to fall into
 the same trap. I don't know how many folks still read ghc-bugs, or the
 trac RSS feeds, so perhaps raise the issue on ghc-users, and point to this
 ticket?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3217#comment:9>
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