internal void ApplyLeftFactoring()
{
var trie = TrieNode.CreateRoot();
foreach (var exp in RHSList)
{
if (exp.IsEpsilon)
{
continue;
}
trie.AddExpression(exp);
}
var alphas = trie.GetMinCommonExpressions();
alphas.Add(Expression.E);
var groupedExpressions = alphas.ToDictionary(a => a, a => new List <Expression>());
//Group them by there alpha and if non then epsilon is its alpha
foreach (var exp in RHSList)
{
var expAlpha = alphas.FirstOrDefault(a => exp.StartsWith(a)) ?? Expression.E;
groupedExpressions[expAlpha].Add(exp);
}
RHSList.Clear();
var primes = new List <NonTerminalSymbol>();
foreach (var grp in groupedExpressions)
{
if (grp.Key == Expression.E)
{
RHSList.AddRange(grp.Value);
}
else
{
var primeSymbol = Grammer.AddRule();
primeSymbol.RHSList.AddRange(grp.Value.Select(e => e.SubExpression(grp.Key.Count)));
RHSList.Add(Expression.Create(grp.Key.Value.Append(primeSymbol)));
primes.Add(primeSymbol);
}
}
foreach (var prime in primes)
{
prime.ApplyLeftFactoring();
}
}
/// <remarks>Solves only 1-level indirect recursion</remarks>
internal void SolveIndirectLeftRecusrion()
{
var newRHS = new List <Expression>(RHSList.Count + 10);
foreach (var exp in RHSList)
{
if ((exp[0] as NonTerminalSymbol)?.RHSList.Any(re => re.Value[0] == this) ?? false)
{
newRHS.AddRange((exp[0] as NonTerminalSymbol).RHSList.Select(re => re.Append(exp.SubExpression(1))));
}
else
{
newRHS.Add(exp);
}
}
RHSList.Clear();
RHSList.AddRange(newRHS);
SolveLeftRecursion(CalcAlphas());
}