public static Dictionary <object, HashSet <SyntaxPredicate> > CalculateFollowSet(
List <ProductionRule> productionRules, Dictionary <object, HashSet <SyntaxPredicate> > firstSet)
{
var result = new Dictionary <object, HashSet <SyntaxPredicate> >();
foreach (var key in firstSet.Keys)
{
result.Add(key, new HashSet <SyntaxPredicate>());
}
bool updated = true;
while (updated)
{
updated = false;
foreach (var productionRule in productionRules)
{
int i = 0;
for (; i < productionRule.Predicates.Count; ++i)
{
if (productionRule.Predicates[i] is KeyedNonTerminalPredicate kp)
{
bool epl = true;
for (int j = i + 1; j < productionRule.Predicates.Count; ++j)
{
if (productionRule.Predicates[j] is TerminalPredicate tp)
{
epl = false;
updated |= result[kp.Key].Add(tp);
break;
}
if (productionRule.Predicates[j] is KeyedNonTerminalPredicate kp2)
{
var f = firstSet[kp2.Key];
foreach (var source in f.Except(EpsilonPredicate.Enumerator()))
{
updated |= result[kp.Key].Add(source);
}
if (!f.Contains(EpsilonPredicate.Instance))
{
epl = false;
break;
}
}
}
if (epl)
{
foreach (var sp in result[productionRule.Key].Except(EpsilonPredicate.Enumerator()))
{
updated |= result[kp.Key].Add(sp);
}
}
}
}
}
}
return(result);
}
public static Dictionary <object, HashSet <SyntaxPredicate> > CalculateFirstSet(List <ProductionRule> productionRules)
{
var result = new Dictionary <object, HashSet <SyntaxPredicate> >();
foreach (var productionRule in productionRules)
{
if (!result.ContainsKey(productionRule.Key))
{
result.Add(productionRule.Key, new HashSet <SyntaxPredicate>());
}
}
bool updated = true;
while (updated)
{
updated = false;
foreach (var productionRule in productionRules)
{
var key = productionRule.Key;
if (productionRule.Length == 0)
{
updated |= result[key].Add(EpsilonPredicate.Instance);
continue;
}
bool epl = true;
foreach (var predicate in productionRule.Predicates)
{
if (predicate is TerminalPredicate)
{
updated |= result[key].Add(predicate);
epl = false;
break;
}
if (predicate is KeyedNonTerminalPredicate kp)
{
var t = kp.Key;
var tset = result[t].Except(EpsilonPredicate.Enumerator());
foreach (var syntaxPredicate in tset)
{
updated |= result[key].Add(syntaxPredicate);
}
if (!result[t].Contains(EpsilonPredicate.Instance))
{
epl = false;
break;
}
}
}
if (epl)
{
updated |= result[key].Add(EpsilonPredicate.Instance);
}
}
}
return(result);
}
