Recursive Decent Parsing:Functions to parse the Toy Grammar III

• Here is the last of the four functions of the Toy Grammar. This grammar rule had several alternatives. A switch() statement selects the right alternative to parse based on what the current look ahead token is.

• Remember, no actions are yet added to these functions. All they do is recognize the input and move on; they don’t do anything with it yet.

• <> => ID | CONST | ‘(’ <> ‘)’

factor(){

switch( tokentype ){

case ID:

scanner();

break;

case CONST:

scanner();

break;

case LEFTPAREN:

scanner();

expression();

if( tokentype != RIGHTPAREN )

error(“Missing ‘)’”);

else

scanner();

break;

default:

error(“Missing ID, CONST, or ‘(’”);

}

}