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Message from discussion doall, dorun, doseq, for
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Chouser  
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 More options Mar 3 2009, 9:30 pm
From: Chouser <chou...@gmail.com>
Date: Tue, 3 Mar 2009 21:30:15 -0500
Local: Tues, Mar 3 2009 9:30 pm
Subject: Re: doall, dorun, doseq, for
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On Tue, Mar 3, 2009 at 2:54 PM, Mark Volkmann <r.mark.volkm...@gmail.com> wrote:

> I agree that using doseq instead of dorun results in code that is
> easier to read. I don't understand though why it is more efficient.
> They both walk the entire sequence, neither holds onto the head and
> both return nil. Why is doseq more efficient than dorun?

A simple doseq does run about as fast as dorun on the same seq.  Bus
something like this would be more likely (let's pretend inc has useful
side-effects):

  (defn f [] (dorun (map #(inc %) (range 10000000))))

  (defn f2 [] (doseq [i (range 10000000)] (inc i)))

The results would be the same, but dorun requires 'map', which creates
another seq.  'doseq' is able to accomplish the same work with less
allocation.

  user=> (time (f))
  "Elapsed time: 1685.796066 msecs"

  user=> (time (f2))
  "Elapsed time: 531.730209 msecs"

--Chouser


 
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