/**
* Start recursive collection of e-transtions to states
* @param Grammar
* @param int number of symbols to look ahead, currently only 0 or 1
* @return void
*/
function collect_non_deterministic(Grammar $Grammar, $k)
{
// avoid recursion by testing if already collected
if (isset($this->etransitions)) {
return;
}
$this->etransitions = array();
// get all rules with our non-terminal as left had side
foreach ($Grammar->get_rules($this->nt) as $r => $rule) {
// create single Item for new state with pointer at start of rule
$Item = LRItem::make($r, $rule, 0);
if (isset($this->la) && $k === 1) {
$Item->lookahead($this->la);
}
// create e-transition to state with single item
$State = LRState::make($Item);
$State->collect_non_deterministic($Grammar, $k);
$this->etransitions[] = $State;
}
}
/**
* Start recursive collection of transtions to stations and states
* @param Grammar
* @param int number of symbols to look ahead, currently only 0 or 1
* @return Void
*/
function collect_non_deterministic(Grammar $Grammar, $k)
{
// avoid recursion by testing if already collected
if (isset($this->transitions)) {
return;
}
$this->transitions = array();
$this->etransitions = array();
$s = $this->Item->current_symbol();
$la = $this->Item->next_symbol();
#1. accept if end of rule
if (is_null($s)) {
return;
}
#2. e-transition to station if symbol is non-terminal
if ($Grammar->non_terminal($s)) {
// LR(0) has no lookahead
if ($k === 0) {
$las = array(null);
} else {
if (is_null($la)) {
// use current look ahead
$las = array($this->Item->lookahead());
} else {
if ($Grammar->is_terminal($la)) {
// use terminal as next lookahead
$las = array($la);
} else {
// -- FOLLOW method -------
$las = $Grammar->follow_set($s);
// -- FIRST method -------
//$ss = $Item->next_symbols();
//$ss[] = $Item->lookahead();
//$las = $Grammar->first_set( $ss );
}
}
}
// create a station for each lookahead symbol
foreach ($las as $la) {
$Station = LRStation::make($s, $la);
$Station->collect_non_deterministic($Grammar, $k);
$this->etransitions[] = $Station;
}
}
#3. Branch advanced item to a new state
$nextItem = $this->Item->make_next();
$State = LRState::make($nextItem);
$State->collect_non_deterministic($Grammar, $k);
$this->transitions[$s] = $State;
}
