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)))))
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