ParseTree parse(Symbol current_symbol, ParseTree root)
{
/*recursive function to parse the tokens*/
/*current_symbol: The symbol currently on top of the stack*/
/*root: The pointer to the root of the relevant subtree of the Parse Tree*/
int i;
char id_or_num[50];
char temp_token[20];
ProductionTable prodtable;
Production production;
List prod_right;
TreeNode tnode = (TreeNode)malloc(sizeof(struct tnode));
strcpy(tnode->name,current_symbol->name);
tnode->type = current_symbol->type;
tnode->line_num = line_num;
//first check if current_symbol is a terminal
if(current_symbol->type == TERMINAL)
{
//Check if the current_symbol is ε. If yes then simply continue
if(strcmp(current_symbol->name, "ε")==0)
{
root->node = tnode;
root->num_branches = 0;
return root;
}
//Check if its TK_ID or TK_NUM to strip additional data
if((strcmp(current_symbol->name, "TK_ID")==0)||(strcmp(current_symbol->name, "TK_NUM")==0))
{
sscanf(current_token,"%*[^:]%*[:]%s",id_or_num);
sscanf(current_token,"%[^:]",current_token);
tnode->id_or_num = (char *)malloc(50*sizeof(char));
strcpy(tnode->id_or_num,id_or_num);
}
//check if current token is a match
if(strcmp(current_symbol->name, current_token)==0)
{
root->node = tnode;
root->num_branches = 0;
//we can eat the current token and move ahead
if(strcmp(current_token,"EOF")!=0)
advance(token_file);
return root;
}
else
{
//Error Handling. return NULL.
fprintf(stderr,"ERROR at line %d:: Expected %s. Found %s.\n",line_num,current_symbol->name,current_token);
exit(1);
}
}
else
{
//this is a nonterminal. so we need to apply the appropriate production from the parsing table
sscanf(current_token,"%[^:]",temp_token);
prodtable = current_symbol->prodtable;
production = findProduction(prodtable, temp_token);
if(production==NULL)
{
//Error Handling. return NULL.
fprintf(stderr,"ERROR at line %d:: Expected symbols are ",line_num);
for(i=0;i<current_symbol->num_first;i++)
printf("%s, ",current_symbol->first[i].symbol->name);
if(current_symbol->nullable==YES)
for(i=0;i<current_symbol->num_follow;i++)
printf("%s, ",current_symbol->follow[i].symbol->name);
printf("Found %s.\n",temp_token);
exit(1);
}
//appropriate production found. add current symbol to tree.
root->node = tnode;
prod_right = production->prod_right;
//now create as many branches at current root as symbols in prod_right.
root->branches = (ParseTree *)malloc(sizeof(ParseTree)*(production->num_symbols));
root->num_branches = production->num_symbols;
for(i=0;i<production->num_symbols;i++)
{
//applying rules for all symbols on right hand side of the rule.
root->branches[i] = (ParseTree)malloc(sizeof(struct ptree));
root->branches[i] = parse(prod_right[i].symbol, root->branches[i]);
}
}
return root;
}
bool Parser::reduce(ParserActionReduce* const r) {
if (r == 0)
return false;
const int productionID = r->getProductionID();
ProductionStub* prod = findProduction(productionID);
if (prod == 0) {
log_ << "fatal error: there is no production with ID = " << productionID << "!\n";
return false;
}
bool result = true;
const std::list<int>& body = prod->getBodyIDs();
std::vector<ParserSymbol*> removedSymbols;
for (std::list<int>::const_reverse_iterator it = body.rbegin();
it != body.rend(); ++it)
{
if (! states_.empty())
states_.pop();
else {
log_ << "fatal error: stack is empty!\n";
result = false;
}
if (! symbols_.empty())
{
if ((*(symbols_.top()) != *it) && (! isProxySymbol(*it, symbols_.top()->getSymbolID())) )
{
log_ << "fatal error: top symbol ('" << symbolID2String(symbols_.top()->getSymbolID());
log_ << "') does not match the symbol in the production's body ('";
log_ << symbolID2String(*it) << "')\n";
log_ << "ProdcutionID = " << productionID << "\n";
result = false;
}
// Attention: this reverses the order of the symbols from the stack!
//
removedSymbols.push_back(symbols_.top());
symbols_.pop();
}
}
symbols_.push(new ParserSymbol(prod->getHeadID()));
const int nextState = gotoState(states_.top(), prod->getHeadID());
if (nextState >= 0)
states_.push(nextState);
else {
log_ << "fatal: no following state found for state ";
log_ << states_.top() << " and symbol " << symbolID2String(prod->getHeadID()) << "\n";
result = false;
}
delete prod;
if (result == true)
expandParseTree(productionID, removedSymbols);
for (size_t i = 0; i < removedSymbols.size(); ++i)
delete removedSymbols[i];
return result;
}
