144 lines
4.4 KiB
Plaintext
144 lines
4.4 KiB
Plaintext
private Node parseStatement() {
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System.out.println("-----> parsing <statement>:");
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Token token = lex.getNextToken();
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// ---------------->>> print <string> or print <expr>
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if ( token.isKind("print") ) {
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token = lex.getNextToken();
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if ( token.isKind("string") ) {// print <string>
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return new Node( "prtstr", token.getDetails(),
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null, null, null );
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}
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else {// must be first token in <expr>
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// put back the token we looked ahead at
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lex.putBackToken( token );
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Node first = parseExpr();
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return new Node( "prtexp", first, null, null );
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}
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// ---------------->>> newline
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}
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else if ( token.isKind("newline") ) {
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return new Node( "nl", null, null, null );
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}
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// --------------->>> <var> = <expr>
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else if ( token.isKind("var") ) {
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String varName = token.getDetails();
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token = lex.getNextToken();
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errorCheck( token, "single", "=" );
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Node first = parseExpr();
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return new Node( "sto", varName, first, null, null );
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}
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else {
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System.out.println("Token " + token +
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" can't begin a statement");
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System.exit(1);
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return null;
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}
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}// <statement>
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private Node parseExpr() {
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System.out.println("-----> parsing <expr>");
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Node first = parseTerm();
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// look ahead to see if there's an addop
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Token token = lex.getNextToken();
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if ( token.matches("single", "+") ||
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token.matches("single", "-")
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) {
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Node second = parseExpr();
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return new Node( token.getDetails(), first, second, null );
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}
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else {// is just one term
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lex.putBackToken( token );
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return first;
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}
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}// <expr>
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private Node parseTerm() {
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System.out.println("-----> parsing <term>");
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Node first = parseFactor();
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// look ahead to see if there's a multop
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Token token = lex.getNextToken();
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if ( token.matches("single", "*") ||
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token.matches("single", "/")
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) {
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Node second = parseTerm();
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return new Node( token.getDetails(), first, second, null );
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}
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else {// is just one factor
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lex.putBackToken( token );
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return first;
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}
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}// <term>
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private Node parseFactor() {
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System.out.println("-----> parsing <factor>");
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Token token = lex.getNextToken();
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if ( token.isKind("num") ) {
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return new Node("num", token.getDetails(), null, null, null );
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}
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else if ( token.isKind("var") ) {
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return new Node("var", token.getDetails(), null, null, null );
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}
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else if ( token.matches("single","(") ) {
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Node first = parseExpr();
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token = lex.getNextToken();
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errorCheck( token, "single", ")" );
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return first;
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}
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else if ( token.isKind("bif0") ) {
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String bifName = token.getDetails();
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token = lex.getNextToken();
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errorCheck( token, "single", "(" );
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token = lex.getNextToken();
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errorCheck( token, "single", ")" );
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return new Node( bifName, null, null, null );
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}
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else if ( token.isKind("bif1") ) {
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String bifName = token.getDetails();
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token = lex.getNextToken();
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errorCheck( token, "single", "(" );
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Node first = parseExpr();
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token = lex.getNextToken();
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errorCheck( token, "single", ")" );
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return new Node( bifName, first, null, null );
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}
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else if ( token.isKind("bif2") ) {
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String bifName = token.getDetails();
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token = lex.getNextToken();
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errorCheck( token, "single", "(" );
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Node first = parseExpr();
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token = lex.getNextToken();
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errorCheck( token, "single", "," );
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Node second = parseExpr();
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token = lex.getNextToken();
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errorCheck( token, "single", ")" );
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return new Node( bifName, first, second, null );
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}
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else if ( token.matches("single","-") ) {
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Node first = parseFactor();
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return new Node("opp", first, null, null );
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}
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else {
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System.out.println("Can't have a factor starting with " + token );
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System.exit(1);
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return null;
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}
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}// <factor>
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