[Haskell-cafe] why cannot i get the value of a IORef variable ?

[zaxis]

thank you! In fact i really donot understand "unsafePerformIO" very much !


Thomas DuBuisson wrote:
> 
> zaxis <z_axis at 163.com> wrote:
>>> let aaa = unsafePerformIO  $ newIORef []
>>> writeIORef aaa [1,2,3]
>>> readIORef aaa
>> [(),(),()]
> 
> What in Haskells name do you think you're doing?  Don't use
> unsafePerformIO like that!  Its unnecessary and a bit concerning,
> really.
> 
> Prelude> :m Data.IORef
> Prelude Data.IORef> x <- newIORef [] :: IO (IORef [Int])
> Prelude Data.IORef> writeIORef x [1,2,3]
> Prelude Data.IORef> readIORef x
> [1,2,3]
> 
> 
>>
>> sincerely!
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