#2641: Make -XExtendedDeafultRules a bit less liberal
------------------------------+---------------------------------------------
Reporter: simonpj | Owner:
Type: feature request | Status: new
Priority: normal | Milestone: 6.12 branch
Component: Compiler | Version: 6.8.3
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown/Multiple
Os: Unknown/Multiple |
------------------------------+---------------------------------------------
Changes (by igloo):
* milestone: => 6.12 branch
Comment:
A couple of thoughts:
`-Wall` would warn about the defaulting. Perhaps in GHCi we could have a
quieter warning on by default, so instead of either
{{{
<interactive>:1:35:
Warning: Defaulting the following constraint(s) to type `()'
`Eq a' arising from a use of `==' at <interactive>:1:35-50
`Test.QuickCheck.Arbitrary a'
arising from a use of `Test.QuickCheck.quickCheck'
at <interactive>:1:0-51
`Show a'
arising from a use of `Test.QuickCheck.quickCheck'
at <interactive>:1:0-51
In the expression: reverse xs == xs
In the first argument of `Test.QuickCheck.quickCheck', namely
`(\ xs -> reverse xs == xs)'
In a stmt of a 'do' expression:
it <- Test.QuickCheck.quickCheck (\ xs -> reverse xs == xs)
}}}
or nothing we could get
{{{
Warning: Defaulting a type to ()
}}}
or
{{{
Warning: Defaulting a type to () (use -fwarn-whatever-it-is for more
detail)
}}}
The other thought is getting very ad-hoc, but I think we only want
defaulting to `()` in an `IO a` type.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2641#comment:1>
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