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A comment on Is Haskell the Cure?. Parent comment

Re:Is Haskell the Cure? by jrockway on Monday October 03, 2011 @04:16PM (#3067841)
If the library developer can prove that a C operation is pure, why shouldn't he tell Haskell about that?
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Re:Is Haskell the Cure? by jrockway on Tuesday October 04, 2011 @12:06AM (#3069307)
And if you don't trust the developer, it's easy to fix his mistake:

    unUnsafePerformIO :: a -> IO a
    unUnsafePerformIO = return
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Re:Is Haskell the Cure? by ezyang on Tuesday October 04, 2011 @02:32AM (#3069677)
Sorry, that doesn't actually work.

    ezyang@ezyang:~$ cat Test.hs
    import System.IO.Unsafe
    unUnsafePerformIO = return
    main = do
      let a = unUnsafePerformIO (unsafePerformIO (putStrLn "boom"))
      a
      a
    ezyang@ezyang:~$ runghc Test.hs
    ezyang@ezyang:~$
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Re:Is Haskell the Cure? by jrockway on Tuesday October 04, 2011 @11:07AM (#3071209)
Yes, true. Patch the library if the annotation is wrong :)
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