Hey everyone,
I've been trying all morning (more than 3 hours) to improve my macro but
with little success...basically what I had before i started fiddling
with it was a macro which would take an expression of the form (1 + 4 *
5 - 1 / 2) and would return the expression in prefix form: (/ (- (* (+
1 4) 5) 1) 2)...it would not handle nested parens and no operator
precedence...This is it:
---------------------------------------------------------------------------------------------------------------------------------------
(defmacro functionize [macro]
`(fn [& args#] (eval (cons '~macro args#))))
(defmacro infix-to-prefix [expr]
(if-not (empty? (filter #(list? %)) '~expr))
(infix-to-prefix
(map #(if (list? %)
(apply (functionize infix-to-prefix) %) %) 'expr))
`(loop [
ops# (filter #(not (number? %)) '~expr)
args# (filter #(number? %) '~expr)
]
(if (empty? ops#) (first args#)
(let [[a# b# & more#] args#]
(recur
(rest ops#)
(conj more#
(list (first ops#) a# b#))))))))
;;usage : (infix-to-prefix (1 + 4 * 6))
;;=> (* (1 + 4) 6)
--------------------------------------------------------------------------------------------------------------------------------------
I know for a fact that the bit after the back-quote works exactly as
explained above...all the new code is above the back-quoted loop - recur
form. all i'm trying to do is replace all the parens at each level with
values calculated recursively using eval on the returned
expression....However i can't seem to go any further...I am literally
about to give up...I know this may not be necessarily the best approach
but i 've worked hard on this and i want to see it succeed!
Any help is greatly appreciated...
Jim
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
