Re: unique identifiers as a separate library

ajb@spamcop.net wrote:

G'day all.

Quoting Sebastian Fischer :

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I have wrapped up (a tiny subset of) GHC's uniques into the package `uniqueid` and put it on Hackage:

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/uniqueid

First off, thanks for this.

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The main difference is due to my fear of depending on the foreign function `genSymZh` which I replaced by a global counting IORef.

Why not depend on this instead?

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/value-supply

Looking at the code for this, I'm somewhat suspicious that it actually works with GHC: -- The extra argument to ``gen'' is passed because without -- it Hugs spots that the recursive calls are the same but does -- not know that unsafePerformIO is unsafe. where gen _ r = Node { supplyValue = unsafePerformIO (genSym r), supplyLeft = gen False r, supplyRight = gen True r } even if that extra Bool argument is enough to fool Hugs, I wouldn't count on it being enough to fool GHC -O2! You probably want to use unsafeInterleaveIO like we do in GHC's UniqSupply library. Also, I'd replace the MVar with an IORef and use atomicModifyIORef for speed. Cheers, Simon