Consider the following grammar rule in the picture below. Write the Java method

Question

Consider the following grammar rule in the picture below. Write the Java method to parse these Simple Expressions using the code below as a reference.

/**

* Use as a reference

*/

S -> ‘if’ e ‘then’ block ‘else’ block

--------------------------------------------

public AST rExpr() throws SyntaxError {

AST t;

if (isNextTok(Tokens.If))

{

scan();

t = new IfTree();

t.addKid(rExpr());

expect(Tokens.Then);

t.addKid(rBlock());

expect(Tokens.Else);

t.addKid(rBlock());

return t;

}

Use this grammar rule please.

Production TYPE "float" TYPE "void S 'return' NAME (E list E SE SE Description FLOAT token VOID token Return statement for void functions Calling void functions GREAT token

Explanation / Answer

Answer: See below:

1. For 'TYPE':

---------------------------------------------------------

public AST rType() throws SyntaxError
   {
       AST t;
       if(isNextTok(Tokens.FLOAT))
       {
           t=new FloatTree();
           scan();
       }
       else if(isNextTok(Tokens.VOID))
       {
           t=new VOIDTree();
           scan();
       }
       return t;
   }

------------------------------------------

2. Return statement of void function:

-------------------------------

public AST rS() throws SyntaxError
   {
       AST t;
       if(isNextTok(Tokens.Return))
       {
           scan();
           t=new ReturnTree();
           t.addKid(rExpr());
           expect(Tokens.SemiColon);
       }
       return t;
   }

--------------------------------

3. Calling of void functions:

-------------------------------------

public AST rName() throws SyntaxError {
       AST t;
       scan();
       if (isNextTok(Tokens.LeftParenthesis)) {
           t = (new CallTree()).addKid(t);
           if (!isNextTok(Tokens.RightParenthesis)) {
               do {
                   t.addKid(rExpr());
                   if (isNextTok(Tokens.Comma)) {
                       scan();
                   } else {
                       break;
                   }
               } while (true);
           }
           expect(Tokens.RightParenthesis);
       }
       return t;
   }

----------------------------------------

4. GREAT token:

---------------------------------------

public AST rE() throws SyntaxError
   {
       AST t, kid=rSE();
       t=new GreatTree();
       if(t==null)
       {
           return kid;
       }
       t.addKid(kid);
       t.addKid(rSE());
       return t;
   }

-----------------------------------------------------

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