Thanks Meikel,
your negative answer actually helped me analyze my problem better and
get the distinction run time / expansion time straight. I figured that
the names of the bindings are already there at expansion time and it's
only the values that I need to retrieve at run time.
So this version
(defmacro let-coll
[ks val-fn & body]
`(let ~(vec (mapcat #(list % `(~val-fn '~%)) ks)) ~...@body))
allows me to do this:
user=> (def m {'a 1 'b 2 'c 3})
#'user/m
user=> (let-coll (a b c) m (list a b c))
(1 2 3)
And although the macro itself looks a bit ugly (suggestions on
improvement welcome!), it expands very cleanly:
user=> (macroexpand-1 '(let-coll (a b c) m (list a b c)))
(clojure.core/let [a (m (quote a)) b (m (quote b)) c (m (quote c))]
(list a b c))
This macro is of course not very useful, it is - for the sake of
simplicity - a stripped-down version of something more sophisticated.
But if it was the real macro, I guess I should have forced the
parameter "ks" to be vector, to make it more look like let, or fn.
Thanks again for all the answers, also the ones from John, which I
might need in the future, but I'm glad I could get away with a single
(more or less) simple macro this time :)
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