Re: [Haskell-cafe] Re: Order of Evaluation
On Fri, May 9, 2008 at 3:46 PM, Achim Schneider [EMAIL PROTECTED] wrote: Miguel Mitrofanov [EMAIL PROTECTED] wrote: Oh, you sure? I was, until you wrote that. But then, I am, as I wouldn't use unsafePerformIO together with IORef's, it's giving me the creeps. So.. what do you use unsafePerformIO together with? In uses where I'm not just debugging stuff, I _usually_ use it with IORefs, for more complex caching behavior than I can get out of the language. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: Order of Evaluation
Hello Luke, Sunday, May 11, 2008, 1:24:04 PM, you wrote: So.. what do you use unsafePerformIO together with? when i call function that in general case depends on the execution order (so it's type is ...-IO x), but in my specific case it doesn't matter. typical example is hGetContents on config file, GetSystemInfo just to get number of processors, string processing via C functions -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Order of Evaluation
Miguel Mitrofanov [EMAIL PROTECTED] wrote: As I understand it Haskell does not specify an order of evaluation and it would therefore be a mistake to write a program which relies on a particular evaluation order. This is the 'unsafe' aspect of unsafePerformIO. Hmm... IMHO unsafePerformIO is 'unsafe' because it can lead to type errors in runtime. At least, that seems to be much more dangerous. Nope. That'd be unsafeCoerce#, which you never heard of, and I did not mention it in this post. Go away. This is not the function you are looking for. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Order of Evaluation
Oh, you sure? quote src=http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-IO-Unsafe.html It is less well known that unsafePerformIO is not type safe. For example: test :: IORef [a] test = unsafePerformIO $ newIORef [] main = do writeIORef test [42] bang - readIORef test print (bang :: [Char]) This program will core dump. This problem with polymorphic references is well known in the ML community, and does not arise with normal monadic use of references. There is no easy way to make it impossible once you use unsafePerformIO. Indeed, it is possible to write coerce :: a - b with the help of unsafePerformIO. So be careful! /quote That's the reason why f has sometimes LESS general type than \x - f x in OCaml. On 10 May 2008, at 01:34, Achim Schneider wrote: Miguel Mitrofanov [EMAIL PROTECTED] wrote: As I understand it Haskell does not specify an order of evaluation and it would therefore be a mistake to write a program which relies on a particular evaluation order. This is the 'unsafe' aspect of unsafePerformIO. Hmm... IMHO unsafePerformIO is 'unsafe' because it can lead to type errors in runtime. At least, that seems to be much more dangerous. Nope. That'd be unsafeCoerce#, which you never heard of, and I did not mention it in this post. Go away. This is not the function you are looking for. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Order of Evaluation
Miguel Mitrofanov [EMAIL PROTECTED] wrote: Oh, you sure? I was, until you wrote that. But then, I am, as I wouldn't use unsafePerformIO together with IORef's, it's giving me the creeps. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Order of evaluation
Jon Harrop wrote: If you have a boolean-or expression: a || b will a be evaluated before b in Haskell as it is in other languages? Yes, although the meaning of the phrase evaluated before is a bit tricky in a lazy language, so it's probably better to state it with denotational semantics alone: _|_ || b = _|_ Maybe you also want to know whether the second argument is evaluated. This is answered by True || _|_ = True False || _|_ = _|_ Regards, apfelmus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
