Hi, Am Sonntag, den 18.08.2013, 21:54 +0200 schrieb Gabor Greif:
> There is also user-supplied Typeable instances which are ignored (with
> a warning?).
at least no Typeabe-specific warning:
Prelude> newtype Age = Age Int
Prelude> instance Typeable Age
Prelude> :m + Data.Typeable
Prelude Data.Typeable> instance Typeable Age
<interactive>:5:10: Warning:
No explicit method or default declaration for `typeOf'
In the instance declaration for `Typeable Age'
It seems that GHC does prevent it in Safe mode, though:
-- Check that if the module is compiled with -XSafe, there are no
-- hand written instances of old Typeable as then unsafe casts could be
-- performed. Derived instances are OK.
; when (safeLanguageOn dflags) $
mapM_ (\x -> when (typInstCheck x)
(addErrAt (getSrcSpan $ iSpec x) typInstErr))
local_infos
(compiler/typecheck/TcInstDcls.lhs)
Greetings,
Joachim
--
Joachim “nomeata” Breitner
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