Nice one Sam. I think you could add order of operations by transforming the form in multiple passes. First /, then *, then + and -. Not the most efficient solution but a start.
Alex On Wed, May 2, 2012 at 6:14 PM, Sam Ritchie <sritchi...@gmail.com> wrote: > Hey Jim, what do you think of something like this? > > (defmacro infix->prefix [form] > (loop [[a op b & more :as form] form] > (if (not op) > a > (recur (cons (list op a b) more))))) > > This transforms the list by plucking off three items at a time, > rearranging them into prefix notation then popping them back onto the list > in the recursion. When only one form's left inside the list, the macro > returns that form, passing it into the compiler. Here's an example > expansion: > > user> (infix->prefix (1 * 2 + 3 - 6)) > (1 * 2 + 3 - 6) > ((* 1 2) + 3 - 6) > ((+ (* 1 2) 3) - 6) > ((- (+ (* 1 2) 3) 6)) > -1 > > On Wed, May 2, 2012 at 1:24 PM, Jim - FooBar(); <jimpil1...@gmail.com>wrote: > >> 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+unsubscribe@**googlegroups.com<clojure%2bunsubscr...@googlegroups.com> >> For more options, visit this group at >> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en> > > > > > -- > Sam Ritchie, Twitter Inc > 703.662.1337 > @sritchie09 > > (Too brief? Here's why! http://emailcharter.org) > > -- > 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 > -- 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
