Initial data commit

Task/Parsing-RPN-calculator-algorithm/EchoLisp/parsing-rpn-calculator-algorithm.l

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+;; RPN (postfix) evaluator
+
+(lib 'hash)
+
+(define OPS (make-hash))
+(hash-set OPS "^" expt)
+(hash-set OPS "*" *)
+(hash-set OPS "/" //) ;; float divide
+(hash-set OPS "+" +)
+(hash-set OPS "-" -)
+
+(define (op? op) (hash-ref OPS op))
+
+;; algorithm : https://en.wikipedia.org/wiki/Reverse_Polish_notation#Postfix_algorithm
+
+(define (calculator rpn S)
+	(for ((token rpn))
+	(if (op? token)
+		(let [(op2 (pop S)) (op1 (pop S))]
+			(unless (and op1 op2) (error "cannot calculate expression at:" token))
+	    	(push S ((op? token) op1 op2))
+	    	(writeln op1 token op2 "→" (stack-top S)))
+	    (push S (string->number token))))
+	(pop S))
+	
+(define (task rpn)
+ (define S (stack 'S))
+ (calculator (text-parse rpn) S ))