public void AddFirst(DotItem item, MutableIntSet output)
{
bool isNullable = tables.AddFirst(item.GetPattern(), item.Position, output);
if (isNullable)
{
output.AddAll(item.LA);
}
}
public void AddFirst(DotItem item, MutableIntSet output)
{
bool isNullable = tables.AddFirst(item.GetPattern(), item.Position, output);
if (isNullable)
{
output.AddAll(item.LA);
}
}
public bool IsTailNullable(DotItem item)
{
return(tables.IsTailNullable(item.GetPattern(), item.Position));
}
public bool HasFirst(DotItem item, int token)
{
return(tables.HasFirst(item.GetPattern(), item.Position, token));
}
public DotItem(DotItem other)
: this(other.production, other.Position)
{
}
// TODO: Separate Closure from the lookahead closuring to get cached closure item sets
private MutableDotItemSet ClosureLr0(MutableDotItemSet itemSet)
{
var result = new MutableDotItemSet();
result.AddRange(itemSet);
bool modified;
do
{
modified = false;
// result may grow during iterations
for (int i = 0; i != result.Count; ++i)
{
var item = result[i];
if (!item.IsReduce && !grammar.IsTerminal(item.NextToken))
{
int X = item.NextToken;
foreach (var childProd in grammar.GetProductions(X))
{
var newItem = new DotItem(childProd, 0)
{
LA = TokenSet.Mutable()
};
var index = result.IndexOf(newItem);
if (index < 0)
{
result.Add(newItem);
modified = true;
}
else
{
var existing = result[index];
existing.LA.AddAll(newItem.LA);
}
}
}
}
}
while (modified);
return result;
}
public DotItem(DotItem other)
: this(other.production, other.Position)
{
}
public bool IsTailNullable(DotItem item)
{
return tables.IsTailNullable(item.GetPattern(), item.Position);
}
public bool HasFirst(DotItem item, int token)
{
return tables.HasFirst(item.GetPattern(), item.Position, token);
}
public int IndexOf(DotItem item)
{
return items.IndexOf(item);
}
public void Add(DotItem item)
{
items.Add(item);
}
private bool IsValueOnlyEpsilonReduceItem(DotItem item, DotState state, int lookahead)
{
if (item.Position != 0
|| grammar.IsStartProduction(item.ProductionId)
|| !grammar.IsTailNullable(item)
|| !item.LA.Contains(lookahead))
{
return false;
}
int epsilonToken = item.Outcome;
foreach (var parentItem in state.Items)
{
if (parentItem == item)
{
continue;
}
if (parentItem.NextToken == epsilonToken)
{
if (!grammar.IsTailNullable(parentItem))
{
// there is at least one rule which needs shift on epsilonToken
return false;
}
if (grammar.HasFirst(parentItem.CreateNextItem(), lookahead))
{
// One of the subseqent non-terms in parentItem can start parsing with current lookahead.
// It means that we need tested epsilonToken production for continue parsing on parentItem.
return false;
}
}
}
return true;
}
