Data commit

Task/Parsing-RPN-to-infix-conversion/Racket/parsing-rpn-to-infix-conversion.rkt

@@ -0,0 +1,32 @@
+#lang racket
+(require racket/dict)
+
+(define (RPN->infix expr)
+  (define-values (res _)
+    (for/fold ([stack '()] [prec '()]) ([t expr])
+      (show t stack prec)
+      (cond
+        [(dict-has-key? operators t)
+         (match-define (list pt at) (dict-ref operators t))
+         (match-define (list y x ss ...) stack)
+         (match-define (list py px ps ...) prec)
+         (define fexpr
+           (cond
+             [(> pt (max px py)) "(~a) ~a (~a)"]
+             [(or (< px pt) (and (= pt px) (eq? at 'r))) "(~a) ~a ~a"]
+             [(or (< py pt) (and (= pt py) (eq? at 'l))) "~a ~a (~a)"]
+             [else "~a ~a ~a"]))
+         (define term (format fexpr x t y))
+         (values (cons term ss) (cons pt ps))]
+        [else (values (cons t stack) (cons +inf.0 prec))])))
+  (car res))
+
+;; the list of operators and their properties
+(define operators '((+ 2 l) (- 2 l) (* 3 l) (/ 3 l) (^ 4 r)))
+
+;; printing out the intermediate stages
+(define (show t stack prec)
+  (printf "~a\t" t)
+  (for ([s stack] [p prec])
+    (if (eq? +inf.0 p) (printf "[~a] " s) (printf "[~a {~a}] " s p)))
+  (newline))