Re: [Haskell-cafe] global variables
Isaac Dupree wrote:
var :: IORef Int
var = {-# EVALUATE_THIS_TEXT_ONLY_ONCE #-} (unsafePerformIO (newIORef 3))
I think I still prefer..
var :: IORef Int
var - newIORef 3
or, more likely..
var :: IORef Int
var - ACIO.newIORef 3
The - syntax should make the intended semantics clear and unambiguous,
so it becomes the problem of individual implementors (not standards
writers) to make sure that whatever optimisations or transformations
that may be appropriate for their implementation preserve those
semantics. (IOW there's no need to worry about what a pragma really
means in operational terms, AFAICS).
The ACIO monad also restricts what programmers may use on the rhs of
the -.
But if you want a good name for the pragma how about this..
var :: IORef Int
var = {-# - #-} (unsafePerformIO (newIORef 3))
:-)
Regards
--
Adrian Hey
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Re: Suggestion for module system (to get rid of many uses of unsafePerformIO)
Stephen Dolan wrote: Would this be useful, useless, or just downright silly? The silence is deafening :-) I think what you're describing seems to be so completely different from Haskell as it is now that that people either don't understand it, or they do understand it and do think it's downright silly, but are just too polite to say that. Maybe you should try writing it up in a more comprehensible form on a Haskell wiki page. I would say that I get worried when people talk about module initialisation and/or (potentially) side effecting imports. I'm not sure if this is a problem with what you're proposing, but I think it's important that we don't get into a situation where the mere presence or absence of some definition in a module can influence program behaviour, even if it isn't referenced by main somehow. Regards -- Adrian Hey ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Suggestion for module system (to get rid of many uses of unsafePerformIO)
I think what you're describing seems to be so completely different from Haskell as it is now that that people either don't understand it, or they do understand it and do think it's downright silly, but are just too polite to say that. Maybe you should try writing it up in a more comprehensible form on a Haskell wiki page. Yeah, that certainly wasn't my most readable piece of writing. I would say that I get worried when people talk about module initialisation and/or (potentially) side effecting imports. I'm not sure if this is a problem with what you're proposing, but I think it's important that we don't get into a situation where the mere presence or absence of some definition in a module can influence program behaviour, even if it isn't referenced by main somehow. No, the point of what I was proposing was that, when a module requires side-effecting initialisation, it would have to be imported inside a do block like any other side-effecting piece of code. At the moment, we have the situation of modules using unsafePerformIO newIORef, which influences program behaviour without being referenced by main. If the import statement was inside a do block, it would be clear when the side-effects are taking place. Regards, Stephen Dolan ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
