> Hi,there!
>
> I need a function that replaces a first found element of list.
> like that,
>
>>(replace-first :a :b [:c :c :a :c :a]
> [:c :c :b :c :a]
> ~~
> ;replace first :a to :b
An interesting problem for a Sunday morning when I ought to be
cleaning the house. :) Here are my (admittedly inexpert) attempts.
First, a sort-of-imperative one:
(defn rmap-first [key value coll]
(let [found (atom false)]
(map (fn [x] (if @found
x
(if (= key x)
(do
(reset! found true)
value)
x)))
coll)))
But that's sort of yucky. So I also did this one, which I sort of like.
(defn replace-first
([key value coll]
(if coll
(if (= key (first coll))
(lazy-cat [value] (next coll))
(lazy-cat [(first coll)] (replace-first key value (next coll)))))))
Although I would have liked it better if I didn't have to use a vector
for the first argument of lazy-cat.
Others will have better solutions, I'm sure.
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