/// <exception cref="NotComputedException"></exception>
public static FollowComputer Compute(LL1Algo algo)
{
_ = algo.Nullable ?? throw new NotComputedException(nameof(algo.Nullable));
_ = algo.First ?? throw new NotComputedException(nameof(algo.First));
var iterations = new List <FollowTable>();
var follow = new FollowTable();
// initialize first iteration
foreach (var A in algo.Thecfg.Nonterminals)
{
follow.Add(A, new FollowResult());
}
do
{
if (iterations.Count == 0)
{
iterations.Add(follow);
}
else
{
iterations.Add(DictUtil.Clone(follow));
}
follow = iterations.Last();
foreach (var prod in algo.Thecfg.Productions)
{
for (int i = 0; i < prod.Rhs.Count; ++i)
{
var Bi = prod.Rhs[i];
if (Bi.Type == Symbol.Types.NonTerminal)
{
// test Bi+1,...,Bk
var rest = prod.Rhs.Skip(i + 1);
follow[Bi].UnionWith(algo.First.Sequence(rest));
if (rest.All(e => e.Type == Symbol.Types.NonTerminal && algo.Nullable[e]) ||
i == prod.Rhs.Count - 1)
{
follow[Bi].UnionWith(follow[prod.Lhs]);
}
}
}
}
// stop loop if no changes between iterations
} while (iterations.Count == 1 ||
!DictUtil.Equal(follow, iterations[iterations.Count - 2]));
return(new FollowComputer(algo, iterations));
}
/// <exception cref="NotComputedException"></exception>
public static FirstComputer Compute(LL1Algo algo)
{
_ = algo.Nullable ?? throw new NotComputedException(nameof(algo.Nullable));
var iterations = new List <FirstTable>();
var first = new FirstTable();
// initialize first iteration
foreach (var A in algo.Thecfg.Nonterminals)
{
first.Add(A, new FirstResult());
}
do
{
if (iterations.Count == 0)
{
iterations.Add(first);
}
else
{
iterations.Add(DictUtil.Clone(first));
}
first = iterations.Last();
foreach (var prod in algo.Thecfg.Productions)
{
foreach (var Bi in prod.Rhs)
{
if (Bi.Type == Symbol.Types.Terminal)
{
first[prod.Lhs].Add(Bi);
break;
}
else
{
first[prod.Lhs].UnionWith(first[Bi]);
}
if (!algo.Nullable[Bi])
{
break;
}
}
}
// stop loop if no changes between iterations
} while (iterations.Count == 1 ||
!DictUtil.Equal(first, iterations[iterations.Count - 2]));
return(new FirstComputer(algo, iterations));
}
