As an example of how to use intaparse to parse arithmetic expressions
(among other things), you might be interested in this
notebook
https://mybinder.org/v2/gh/bhugueney/binder-test/master?filepath=Clojure.ipynb
On Saturday, August 18, 2018 at 2:02:25 PM UTC+2, ckry...@gmail.com wrote:
>
> Hi,
> I am ne to Clojure, and trying to make arithmetic simplifier
> so it can take string in for `1x + 3y -4x + 8 -1y` and return "-3x + 2y +8"
> Currently, I am stuck with a `make-ast` function, where load-string loads.
> it can't load string with variables.
>
> (def precedence '{* 0, / 0
> + 1, - 1})
>
> (def ops {'* *
> '+ +
> '- -
> '/ /})
>
> (defn order-ops
> "((A x B) y C) or (A x (B y C)) depending on precedence of x and y"
> [[A x B y C & more]]
> (let [ret (if (<= (precedence x)
> (precedence y))
> (list (list A x B) y C)
> (list A x (list B y C)))]
> (if more
> (recur (concat ret more))
> ret)))
>
> (defn add-parens
> "Tree walk to add parens. All lists are length 3 afterwards."
> [s]
> (clojure.walk/postwalk
> #(if (seq? %)
> (let [c (count %)]
> (cond (even? c) (throw (Exception. "Must be an odd number of forms"))
> (= c 1) (first %)
> (= c 3) %
> (>= c 5) (order-ops %)))
> %)
> s))
>
> (defn make-ast
> "Parse a string into a list of numbers, ops, and lists"
> [s]
> (-> (format "'(%s)" s)
> (.replaceAll , "([*+-/])" " $1 ")
> load-string
> add-parens))
>
>
> (defn simplify-seq
> "Simplify sequence of vars"
> [s]
> (println s)
> )
>
> (def eval-ast
> (partial clojure.walk/postwalk
> #(if (seq? %)
> ;(simplify-seq %)
> (let [[a o b] %]
> ((ops o) a b))
> %)))
>
> (defn evaluate [s]
> "Parse and evaluate an infix arithmetic expression"
> ;(eval-ast (make-ast s))
> (def ast (make-ast s))
> (println ">>> DEBUG AST:" ast)
> (let [res (eval-ast ast)]
> (println ">>> DEBUG res:" res )))
>
>
> (defn -main
> "Read from STDIN"
> [& args]
> ;
> ;(loop [i 0]
> ; (when (< i n)
> ; (def a (read-line))
> ; (def new (split a #"\s+"))
> ; (println ( + (Integer/parseInt (get new 0)) (Integer/parseInt (get new
> 1)) ))
> ; (recur (inc i))
> ; ))
>
> (loop [input (read-line)]
> (if (= ":done" input)
> (println (evaluate input))
> (recur (read-line)))))
>
>
--
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 unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
