[GHC] #14551: GHCi ignores -XMonomorphismRestriction and -XNoExtendedDefaultRules

[GHC]

#14551: GHCi ignores -XMonomorphismRestriction and -XNoExtendedDefaultRules
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  GHCi              |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by dfeuer:

Old description:

> Because of the way the GHCi defaults are applied, specifying
> `-XMonomorphismRestriction` or `-XNoExtendedDefaultRules` on the GHCi
> command line doesn't actually make those take effect at the interactive
> prompt. They get reset to their interactive defaults afterwards. This is
> rather surprising, and I think it should be fixed.
>
> One option is to dig through the parsed flags after setting the defaults
> to try to find these, but that sounds unpleasant. We're slowly
> accumulating hacks in this area, and it would be nice to find a better
> approach.

New description:

 Because of the way the GHCi defaults are applied, specifying
 `-XMonomorphismRestriction` or `-XNoExtendedDefaultRules` on the GHCi
 command line doesn't actually make those take effect at the interactive
 prompt. They get reset to their interactive defaults afterwards. This is
 rather surprising, and I think it should be fixed.

 {{{
 dfeuer at squirrel> ghci -XMonomorphismRestriction
 Prelude> x = 3
 Prelude> :t x
 x :: Num t => t   -- What? I said I wanted the restriction!
 Prelude> :set -XMonomorphismRestriction
 Prelude> y = 3
 Prelude> :t y
 y :: Integer
 }}}

 One option is to dig through the parsed flags after setting the defaults
 to try to find these, but that sounds unpleasant. We're slowly
 accumulating hacks in this area, and it would be nice to find a better
 approach.

--

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14551#comment:1>
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