Christophe Grand a écrit :
> You also can do something like this:
>
> (defmacro let-eval [vars expr]
> (let [bindings (mapcat #(list (list `quote %) %) vars)]
> `(eval (list 'let [...@bindings] ~expr))))
>
Hmm... not quite:
user=> (let [x [2 3]] (let-eval [x] '(rest x)))
(3)
user=> (let [x '(2 3)] (let-eval [x] '(rest x)))
java.lang.ClassCastException: java.lang.Integer cannot be cast to
clojure.lang.IFn (NO_SOURCE_FILE:0)
The following code fixes this bug:
(defmacro let-eval [vars expr]
(let [bindings (mapcat #(list (list `quote %) (list `list ``quote %))
vars)]
`(eval (list 'let [...@bindings] ~expr))))
user=> (let [x '(2 3)] (let-eval [x] '(rest x)))
(3)
user=> (let [x 12] (let-eval [x] '(+ x 15)))
27
But maybe this is better:
(defmacro let-eval [bindings expr]
(let [binding-forms (map #(list `quote %) (take-nth 2 bindings))
expr-forms (map #(list `list ``quote %) (take-nth 2 (rest
bindings)))]
`(eval (list 'let [~@(interleave binding-forms expr-forms)] ~expr))))
user=> (let-eval [x 12] '(+ x 15))
27
user=> (let-eval [x '(2 3)] '(rest x))
(3)
user=> (let-eval [[x y] [2 3]] '(+ x y))
5
Christophe
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