> So the problem is solved for me, although I have to use eval. I'm not
> sure exactly how dirty this trick is and especially *why* it is
> considered a "smell". I read it on Paul Graham's "On Lisp" and he
> vehemently opposes its use but he doesn't explain why or where it is
> acceptable. Note that he also considered Common Lisp "let*" a smell,
> which is standard practice in Clojure (and in fact there's no
> equivalent of Common Lisp "let"). So maybe we are just making too much
> a big deal of this "eval" thing.
>
It is considered bad because eval is for dynamic evaluation. In this
case you use it at macro time, which shouldn't be necessary most of
the time.
(defn my-complex-function [] ....)
(defmacro insert-the-result-of-the-complex-function []
(my-complex-function))
In your case, as often for strange macro, first write a function that
does the job:
(defn extract-keyword-and-generate-code [].....)
(defmacro generate-methods []
`(do
~@(extract-keyword-and-generate-the-code)))
If you have to use an eval, I find it nicer to use it to compute the
code, not to actually define things.
(defmacro generate-methods [expr]
`(do
~@(extract-keyword-and-generate-the-code (eval expr))))
That way you can often work the eval out, by limiting the kind of
possible exprs.
(If it is only a symbol or a list of keywords, for example)
Anyway, that's just a suggestion. Your solution works too.
Best,
Nicolas.
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