Write a Java program (using JFlex/Cup) to interpret WAE expressions. The CFG for

Question

Write a Java program (using JFlex/Cup) to interpret WAE expressions. The CFG for WAE expressions is given below: ::= SEMI ::= | (+ > | (- > | (with { } > | You will write a main program, called WAE.java, that prompts the user with wae> . The user can enter a WAE expression at the prompt or type exit to exit the WAE interpreter. If the user enters a WAE expression, your program should verify that it is a valid expression. If the expression is valid, it should be evaluated and the value of the expression should be printed: Otherwise and error message should be reported. Sample Run: $ java WAE WAE> {with {x 3} {with {y 4} {with {z 5} {+ x {+ y z} } } } } The value is 12 WAE> (with {x 3} {with {y 4} {+ y z} } Syntax Error WAE> {with {x 3} {with {y 4} {+ y z} } } Semantic Error

Explanation / Answer

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexMatches {

   public static void main( String args[] ) {
      // String to be scanned to find the pattern.
      String line = "This order was placed for QT3000! OK?";
      String pattern = "(.*)(\d+)(.*)";

      // Create a Pattern object
      Pattern r = Pattern.compile(pattern);

      // Now create matcher object.
      Matcher m = r.matcher(line);
      if (m.find( )) {
         System.out.println("Found value: " + m.group(0) );
         System.out.println("Found value: " + m.group(1) );
         System.out.println("Found value: " + m.group(2) );
      }else {
         System.out.println("NO MATCH");
      }
   }
}

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