Thanks miner! On Friday, June 24, 2016 at 10:20:54 PM UTC+2, miner wrote: > > Not exactly the same problem, but you might like to see an infix > implementation from “The Joy of Clojure” by Fogus and Chouser. > > http://fogus.me/fun/unfix/infix-src.html > > The “Joy” code makes intermediate calculations as it goes. I tweaked it a > bit to make a data-reader that only does the infix to prefix > transformation. That’s probably closer to what you want. > > https://gist.github.com/miner/5224709 > > Note: the “Joy” code uses vector notation for grouping. You would have to > adapt it to use lists. > > Here’s the relevant code from my gist, leaving out the data-reader part: > > (def && #(and % %2)) > (def || #(or % %2)) > > (def ops '[- + * / < > && || =]) > (def rank (zipmap ops (iterate inc 1))) > (def op? rank) > > (defn infix > [[a b & [c d e & m]]] > (cond > (vector? a) (recur (list* (infix a) b c d e m)) > (vector? c) (recur (list* a b (infix c) d e m)) > (op? b) (if (and d (< (rank b 0) (rank d 0))) > (recur (list a b (infix (list* c d e m)))) > (recur (list* (list b a c) d e m))) > :else a)) > > ;; example > (infix '[1 + 3 * 4 - 5]) > ;=> (+ 1 (- (* 3 4) 5)) > > > > On Jun 24, 2016, at 2:28 PM, Botond Balázs <balazs...@gmail.com > <javascript:>> wrote: > > > > Hi, > > > > I'm working through Clojure for the Brave and True and there's a little > exercise at the end of Chapter 7: > > > > Create an infix function that takes a list like (1 + 3 * 4 - 5) and > transforms it into the lists that Clojure needs in order to correctly > evaluate the expression using operator precedence rules. > > > > I ended up implementing the shunting yard algorithm in Clojure to solve > it (65 lines, many functions), but I have the suspicion that this exercise > isn't meant to be this complicated and that I'm missing a very obvious and > elegant solution. What do you think? > > > > Thanks, > > Botond > >
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