Well obviously if you can get something to be tail-recursive you won't have
the stack overflows, and the thing in your code that prevents tail recursion
is having to cons the result of the recursive call. So let's try this:
(defn remove-first
[syb lst]
(let [[before after]
(loop [b [] a lst]
(if (empty? lst)
[b a]
(if (= syb (first a))
[b (rest a)]
(recur (cons (first a) b) (rest a)))))]
(concat (reverse before) after)))
user=> (remove-first 4 '(1 5 3 4 2 6 674 4 2))
(1 5 3 2 6 674 4 2)
I'm interested if somebody comes up with something more efficient, i.e. that
doesn't require the reversal.
Gary
On Sat, Jul 24, 2010 at 11:41 AM, nickikt <nick...@gmail.com> wrote:
> Hallo all,
>
> I'm working trough Essentials of Programming Languages. I'm trying to
> right a function like this one:
>
> (defn scheme-remove-first [syb lst]
> (if (empty? lst)
> '()
> (if (= (first lst) syb)
> (rest lst)
> (cons (first lst) (scheme-remove-first syb (rest lst))))))
>
> in a idiomatic clojure way (this is just a scheme to clojure 1:1
> version). I don't like that this function produces stack overflows.
>
> I tried some stuff but I it (almost) semantically correct working but
> I didn't like my code. Can anyone come up with a good version?
>
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Gary Fredericks
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www.gfredericks.com
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