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Comment by prospero | Hacker News Reader

The function you're looking for is 'reset!'

Ah, thank you.

But what I really want it something that doesn't require dereferencing syntax:

    (zet! c (* c x))

This would work: http://gist.github.com/536715

I'm not sure wether this is good style. Probably not.

Edit: Bah. Fixed an error.

'replace-in-form' is a tree-replace, which in Clojure is done with clojure.walk/postwalk-replace. The clojure.walk package is basically tree-map stuff.

Sadly, as far as I know, you need to roll your own tree-reduce.

Thanks for that. I did look at clojure.walk, I just didn't look close enough.

If you evaluate your expression on two different threads, the value of c is non-deterministic. On the other hand, if you call

    (swap! c (partial * 2))

on two separate threads, c will always end up 4x the original value.

These limitations exist for a reason.

It's worth noting you could also write:

    (swap! c * 2)

Yeah, I just thought that looked close enough to infix notation to be confusing.

Also, where did you find reset! ? It's not on the atoms page in the main documents.

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