[Haskell-cafe] Re: [Haskell] IVars
conal at conal.net
Mon Dec 10 00:22:24 EST 2007
Thanks. I don't know for what uses of IVars the difference in
expressiveness is helpful, but now I get that the difference is there.
Cheers, - Conal
On Dec 9, 2007 2:08 PM, Benja Fallenstein <benja.fallenstein at gmail.com>
> Hi Conal,
> On Dec 9, 2007 6:09 PM, Conal Elliott <conal at conal.net> wrote:
> > > readIVar' :: IVar a -> a
> > > readIVar' = unsafePerformIO . readIVar
> > > so, we do not need readIVar'. it could be a nice addition to the
> > libraries, maybe as "unsafeReadIVar" or "unsafeReadMVar".
> > The same argument applies any to pure function, doesn't it? For
> instance, a
> > non-IO version of succ is unnecessary. My question is why make readIVar
> > blocking IO action rather than a blocking pure value, considering that
> > always returns the same value?
> From the rest of Marc's post, I understood the point to be that
> readIVar lets you do something that readIVar' does not let you do:
> block until the IVar is written, then continue *without* first
> evaluating the thunk in the IVar to WHNF. I haven't used IVars myself,
> so this isn't informed by hands-on experience, but it does sound
> sensible to me that "block until the IVar has been written" and
> "evaluate the thunk to WHNF" should be separable.
> All the best,
> - Benja
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