Recursive Decent Parsing:Error Handling by finding the semi-colon

To complete the panic-mode error recovery, the topmost parsing function must detect the failure to parse and skip forward until a semi-colon is found. Once the semi-colon is found, one more token of look ahead is read; this prepares the parser to resume parsing after the statement with the syntax error. The code for this looks something like this:

parser(){

scanner(); /* load first look-ahead token */

while( tokentype != T_EOF ){

switch( tokentype ){

case ID:

if( ! assignment() )

panic(); /* recover */

break;

/* other statement types will go here */

default:

errprint(“Unknown statement type”);

panic(); /* recover */

}

}

}

/* Skip forward to EOF or to after next semi-colon */

panic(){

while( tokentype != T_SEMI

&& tokentype != T_EOF)

scanner();

if( tokentype == T_SEMI )

scanner(); /* skip the ‘;’ */

}