Andrei,
You could just bind another local variable in the loop form:
(loop [ps pairs
ret {}
ffps (ffirst ps)]
(cond (empty? ps) ret
(some-test ffps) (recur (rest ps) (add-to-result ret ffps) (ffirst
(rest ps)))
:true (recur (rest ps) (do-sth-else ret ffps) (ffirst (rest ps)))) )
I think I like Andrew's solution better though.
But you probably want to use 'reduce' instead of 'loop' anyway:
(reduce (fn [ret [key val]] (if (some-test key) (add-to-result ret key)
(do-sth-else ret key))) {} pairs)
Notice how you can destructure each pair in a convenient way.
BTW, do you really mean to call 'add-to-result' and 'do-sth-else' with a map
and a key but no value?
Have all good days,
David Sletten
On Oct 28, 2010, at 8:49 PM, andrei wrote:
> Hi,
>
> I have a code similar to this:
>
> (def pairs (list [1 :a] [2 :b] [3 :c]))
> ...
> (loop [ps pairs, ret {}]
> (cond (empty? ps) ret
> (some-test (first (first ps))) (recur (rest ps) (add-to-
> result ret (first (first ps))))
> :true (recur (rest ps) (do-smth-else ret (first (first
> ps))))))
>
> You can see that string (first (first ps)), which actually gets first
> element of a first vector in pairs, occur many times. I can't move it
> before cond, since ps may be empty and evaluating of (first (first
> ps)) will produce an error (ok, it won't, but in general case it may).
> Is there another way to simplify code to not repeat one form several
> times?
>
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