#1877: Change the meaning of -fextended-default-rules
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Reporter: simonmar | Owner:
Type: task | Status: new
Priority: normal | Milestone: 6.10 branch
Component: GHCi | Version: 6.8.1
Severity: normal | Resolution:
Keywords: | Difficulty: Easy (1 hr)
Testcase: | Architecture: Unknown
Os: Unknown |
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Comment (by simonpj):
I'm missing something.
* If you put `-fextended-default-rules` (or a corresponding `-X` language
flag) in a module, it should apply to that module.
* If you `:set -fno-extended-default-rules` at the GHCi prompt, it should
switch it off for GHCi.
Ah, hmm, maybe I see. Say you `:set -fallow-overlapping-instances` at the
GHCi prompt. That setting ''also'' applies when GHCi compiles a module,
doesn't it? If you didn't want overlapping instances in the module
there's no way to switch it off, short of putting `-fno-allow-overlapping-
instances` in the module, which seems wrong.
But in the case of extended-defaults, GHCi typically has it on, but we
''don't'' want to have it on by default for a module. That's a new
situation. An ad-hoc solution would be to splat the flags with `-fno-
extended-defaults` just before GHCi compiles a module.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1877#comment:5>
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