//computes DirectFirsts, Firsts for non-terminals and productions
private static void ComputeFirsts(GrammarData data)
{
//compute prod direct firsts and initialize NT.Firsts
foreach (var nt in data.NonTerminals) {
foreach (var prod in nt.Productions) {
foreach (var term in prod.RValues) {
prod.DirectFirsts.Add(term);
nt.DirectFirsts.Add(term);
nt.Firsts.Add(term);
if (!term.IsSet(TermOptions.IsNullable)) break; //foreach term
}
}
}//foreach nt
//propagate NT.Firsts
int time = 0;
var done = false;
var newSet = new BnfTermSet();
while (!done) {
done = true;
foreach (var nt in data.NonTerminals) {
newSet.Clear();
foreach (var first in nt.Firsts) {
var ntFirst = first as NonTerminal;
if (ntFirst != null && ntFirst._lastChanged >= nt._lastChecked)
newSet.UnionWith(ntFirst.Firsts);
}
nt._lastChecked = time++;
var oldCount = nt.Firsts.Count;
nt.Firsts.UnionWith(newSet);
if (nt.Firsts.Count > oldCount) {
done = false;
nt._lastChanged = time;
}
}//foreach nt
}//while
//compute prod.Firsts
foreach (var nt in data.NonTerminals) {
foreach (var prod in nt.Productions) {
prod.Firsts.UnionWith(prod.DirectFirsts);
foreach (var directFirst in prod.DirectFirsts) {
var ntDirectFirst = directFirst as NonTerminal;
if (ntDirectFirst != null)
prod.Firsts.UnionWith(ntDirectFirst.Firsts);
}//foreach directFirst
}//foreach prod
}//foreach nt
}
//computes DirectFirsts, Firsts for non-terminals and productions
private static void ComputeFirsts(GrammarData data)
{
//compute prod direct firsts and initialize NT.Firsts
foreach (var nt in data.NonTerminals)
{
foreach (var prod in nt.Productions)
{
foreach (var term in prod.RValues)
{
prod.DirectFirsts.Add(term);
nt.DirectFirsts.Add(term);
nt.Firsts.Add(term);
if (!term.IsSet(TermOptions.IsNullable))
{
break; //foreach term
}
}
}
}//foreach nt
//propagate NT.Firsts
int time = 0;
var done = false;
var newSet = new BnfTermSet();
while (!done)
{
done = true;
foreach (var nt in data.NonTerminals)
{
newSet.Clear();
foreach (var first in nt.Firsts)
{
var ntFirst = first as NonTerminal;
if (ntFirst != null && ntFirst._lastChanged >= nt._lastChecked)
{
newSet.UnionWith(ntFirst.Firsts);
}
}
nt._lastChecked = time++;
var oldCount = nt.Firsts.Count;
nt.Firsts.UnionWith(newSet);
if (nt.Firsts.Count > oldCount)
{
done = false;
nt._lastChanged = time;
}
} //foreach nt
} //while
//compute prod.Firsts
foreach (var nt in data.NonTerminals)
{
foreach (var prod in nt.Productions)
{
prod.Firsts.UnionWith(prod.DirectFirsts);
foreach (var directFirst in prod.DirectFirsts)
{
var ntDirectFirst = directFirst as NonTerminal;
if (ntDirectFirst != null)
{
prod.Firsts.UnionWith(ntDirectFirst.Firsts);
}
} //foreach directFirst
} //foreach prod
} //foreach nt
} //method
