Recursive Descent Parsing:Coding A Very Small Grammar

• Another small example of translating a grammar into recursive-descent parsing functions. Terminal symbols are matched directly; non-terminals turn into function calls:

<> => ID ‘=‘ ( <> | CONST ) ‘;’

<> => CONST

stmt(){

if( tokentype != ID )

error(“Missing identifier”);

scanner(); /* get the next lookahead token */

if( tokentype != EQUALS )

error("Missing ‘=’");

scanner(); /* get the next lookahead token */

switch( tokentype ){

case CONST:

scanner(); /* get next lookahead token */

break;

default:

expr(); /* non-terminal is a function */

break;

}

if( tokentype != SEMICOLON )

error("Missing ‘;’");

scanner(); /* get the next lookahead token */

}

expr(){

if( tokentype != CONST )

error(“Missing constant”);

scanner(); /* get next lookahead token */

}