> And it's implementation is not that trivial:
Excellent point! I've modified --> so that now it's even more versatile and
only evaluates the functions once.
Now this is possible:
user=> (--> 1 (+ 1 _) (do (println "sideeffect!") _) (hash-map :a _ :b
(+ 3 _)) :b)
sideeffect!
5
It now requires an additional replace-all function (a modified replace):
(defn replace-all
[smap coll]
(if (vector? coll)
(reduce
(fn [v i]
(if-let [e (find smap (nth v i))]
(assoc v i (val e))
v
))
coll
(range (count coll))
)
(map
#(if-let [e (find smap %)]
(val e)
(if (seq? %)
(replace-all smap %)
%
)
)
coll
)
)
)
(defmacro -->
([x] x)
([x form]
(if (seq? form)
`(let [~'_ ~x] ~form)
(list form x)
)
)
([x form & more]
; cache the result of the first form
(let [_ `(--> ~x ~form)]
`(--> ~_ ~...@more)
)
)
)
- Greg
On Jul 6, 2010, at 11:55 AM, Meikel Brandmeyer wrote:
> Hi,
>
> On Jul 6, 5:47 pm, Stuart Halloway <[email protected]> wrote:
>
>> There is not general agreement that something like --> is more readable. (I
>> for one disagree, at least so far.)
>
> And it's implementation is not that trivial:
>
> user=> (macroexpand '(--> (launch-rockets-if-called-twice)
> (call :first _ :second _)))
> (call :first (launch-rockets-if-called-twice) :second (launch-rockets-
> if-called-twice))
>
> Maybe there is just not much need for such a macro (at least for me,
> don't for the generality of users). 99% of my use cases can be handled
> with -> or ->> (or a combination there of).
>
> Sincerely
> Meikel
>
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