[Haskell-cafe] Re: Re: Haskell Propeganda

[Ben Franksen]

Don Stewart wrote:
> ashley:
>> Thomas Davie wrote:
>> >I'd be interested to see your other examples -- because that error is
>> >not happening in Haskell!  You can't argue that Haskell doesn't give you
>> >no segfaults, because you can embed a C segfault within Haskell.
>> 
>> This segfaults on my x86_64 Linux box:
>> 
>>   module Main where
>>   import Data.Typeable
>>   import Data.IORef
>>   data T = T
>>   instance Typeable T where
>>     typeOf _ = typeOf (undefined :: IORef ())
>>   main :: IO ()
>>   main = writeIORef (maybe undefined id (cast T)) ()
>> 
>> You'll note nothing marked "Foreign" or "unsafe", and only the base
>> library used. Does the segfault "happen in Haskell" or not?
> 
> You just wrote unsafeCoere# a different way:
> 
>         typeOf T = typeOf (undefined :: IORef ())
> 
> Manual Typeable deriving should probably be disabled :-)

But then we need stand-alone deriving clause, otherwise you are lost if
someone didn't derive Typeable in her library. We need stand-alone deriving
anyway.

Cheers
Ben