Predictive_Parser::Predictive_Parser(CFG *grammar) {
//init vars
this->grammar = grammar;
first = new map<string, set<string>*> ();
follow = new map<string, set<string>*> ();
subset_first = new map<pair<string,int>,set<string>*>();
parse_table = new Parse_Table_Entry*[grammar->get_nonterminals()->size()];
//size = size of terminals + 1 (input end marker)
for (unsigned int i = 0; i < grammar->get_nonterminals()->size(); ++i)
parse_table[i] = new Parse_Table_Entry[grammar->get_terminals()->size() + 1];
//calculate first
set<string>* nonterminals = grammar->get_nonterminals();
for (set<string>::iterator it = nonterminals->begin(); it
!= nonterminals->end(); ++it) {
calc_first(*it);
}
//calculate follow
calc_follow();
//generate parsing table
generate_table();
}
void LL_construct()
{
try
{
prepare_nonterminals();
calc_first();
print_first();
calc_follow();
print_follow();
parse_table_generate();
print_parse_table();
}
catch (ConstructException &e)
{
puts(e.message);
puts("Syntax analyzer construct failed.");
}
}
/* Calculates the value of FOLLOW for all nonterminals (and terminals
while we're at it, but they're not useful). Sets
symbols[].follow. */
static void
precalc_follow (void)
{
int i;
for (i = 0; i < n_symbols; i++)
set_init (&symbols[i].follow);
set_add (&find_symbol (G[0].left)->follow, '$');
for (;;)
{
int added = 0;
for (i = 0; i < n_grammar; i++)
{
const struct production *prod;
struct symbol *A;
int j;
prod = &G[i];
A = find_symbol (prod->left);
for (j = 0; j < prod->n_right - 1; j++)
{
struct symbol *B;
struct set first_Beta;
B = find_symbol (prod->right[j]);
calc_first (&first_Beta,
&prod->right[j + 1], prod->n_right - (j + 1));
added |= set_merge (&B->follow, &first_Beta, 0);
if (set_contains (&first_Beta, 0))
added |= set_merge (&B->follow, &A->follow, 1);
set_free (&first_Beta);
}
if (prod->n_right > 0)
{
struct symbol *B = find_symbol (prod->right[prod->n_right - 1]);
added |= set_merge (&B->follow, &A->follow, 1);
}
}
if (!added)
break;
}
if (debug)
{
printf ("FOLLOW function:\n");
for (i = 0; i < n_symbols; i++)
{
struct symbol *sym = &symbols[i];
if (!sym->nonterminal)
continue;
printf ("\tFOLLOW(%c) = ", sym->sym);
set_print (&sym->follow);
putchar ('\n');
}
}
}
void Predictive_Parser::calc_first(string head) {
//if already calculated then return
if (first->find(head) != first->end())
return;
vector<vector<string>*> * productions =
(*(grammar->get_productions()))[head];
//init set
set<string> * production_first = new set<string> ();
(*first)[head] = production_first;
//terminal added from this production
int added;
//loop on productions
for (unsigned int i = 0; i < productions->size(); ++i) {
//init subset of this production
(*subset_first)[make_pair(head,i)] = new set<string>();
added = 0;
//loop on tokens of specific production
for (unsigned int j = 0; j < productions->at(i)->size(); ++j) {
string token = productions->at(i)->at(j);
//if terminal
if (grammar->get_terminals()->find(token)
!= grammar->get_terminals()->end()) {
++added;
production_first->insert(token);
//add to subset first of this production
subset_first->find(make_pair(head,i))->second->insert(token);
break;
} else {
//NON terminal
if (token == EPSILON_TOKEN)
continue;
//wasn't calculated before
if (first->find(token) == first->end()) {
calc_first(token);
}
bool has_epsilon = false;
set<string> * token_first = first->find(token)->second;
set<string>::iterator it = token_first->begin();
for (; it != token_first->end(); ++it) {
if ((*it) == EPSILON_TOKEN)
has_epsilon = true;
else {
++added;
production_first->insert(*it);
//add to subset first of this production
subset_first->find(make_pair(head,i))->second->insert(*it);
}
}
//if first of token doesn't contain epsilon then
//no need to see the rest of this production
if (!has_epsilon)
break;
}
}
//add epsilon to first of this non terminal
if (added == 0){
production_first->insert(EPSILON_TOKEN);
//add to subset first of this production
subset_first->find(make_pair(head,i))->second->insert(EPSILON_TOKEN);
}
}
}
