On Sun, Aug 24, 2008 at 6:02 PM, budu <[EMAIL PROTECTED]> wrote:
>
> Well, for now only the value s used by the parser macro is really
> needed.
I think you misunderstood me, but I'm not too sure. Anyway, here's an attempt:
(defn match-forms [p s]
(if (= '_ p) []
(loop [p p s s vars []]
(cond
(and (= 0 (count p)) (= 0 (count s))) vars
(= 0 (count s)) nil
:else (let [[fp & rp] p [fs & rs] s]
(cond
;; wildcard pattern
(= '_ fp) (recur rp rs vars)
;; rest
(and (symbol? fp) (= '& fp))
(conj vars (first rp) (conj rs fs))
;; add variable to bindings
(symbol? fp) (recur rp rs (conj vars fp fs))
;; match a symbol
(and (seq? fp) (= 'quote (first fp)))
(if (= fs (second fp)) (recur rp rs vars) nil)
;; not matching
true nil))))))
(defmacro match [value & clauses]
(when (and clauses (= 0 (rem (count clauses) 2)))
(let [[c1 c2 & cr] clauses
syms (take-nth 2 (match-forms c1 c1))]
`(if-let m# (take-nth 2 (rest (match-forms '~c1 ~value)))
(let [~(vec syms) (vec m#)]
~c2)
(match ~value [EMAIL PROTECTED])))))
The trick here is I run match-forms once at compile time to get the
list of symbols that will need to be bound, even though I don't have
the real values yet. I use that list to set up a "let" expression.
At runtime, I run match-forms again, but only take the values part and
drop that into the "let" that I set up at compile time.
That's probably not the best way to solve the problem, but it is *a*
way, and may help you find a more correct solution. ...and since I
don't really understand what you're trying to do, I had only limited
tests that I could try, so I've probably introduced some new bugs.
But at the very least, your original examples now work:
user=> (match '(1 2 3) (a b c) (list c b a))
(3 2 1)
user=> (let [z 4] (match '(1 2 3) (a b c) (list z c b a)))
(4 3 2 1)
--Chouser
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
-~----------~----~----~----~------~----~------~--~---
