protected EmptyParser(EmptyParser other, ParserCloneArgs args)
: base(other, args)
{
}
void FixRecursiveGrammars()
{
var empty = new EmptyParser();
var alternates = Children.OfType <AlternativeParser>();
var first = new List <Parser>();
var second = new List <Parser>();
foreach (var alt in alternates.Distinct().ToList())
{
first.Clear();
second.Clear();
Parser separator = null;
for (int i = 0; i < alt.Items.Count; i++)
{
Parser item = alt.Items[i];
if (item != null && item.IsLeftRecursive(alt))
{
var seqs = item.Scan(filter: p => {
if (ReferenceEquals(p, alt))
{
return(false);
}
if (p is SequenceParser seq && seq.Items.Count > 0 && seq.Items[0].IsLeftRecursive(alt))
{
seq.Items[0] = empty;
return(true);
}
return(false);
}).OfType <SequenceParser>();
foreach (var seq in seqs)
{
separator = seq.Separator;
seq.Items.RemoveAt(0);
}
if (!item.IsLeftRecursive(alt))
{
second.Add(item);
}
else
{
Debug.WriteLine(string.Format("Warning: Item in alternate is still recursive {0}", item.DescriptiveName));
}
}
else
{
first.Add(item);
}
}
if (second.Count > 0)
{
Debug.WriteLine(string.Format("Fixing recursion in alternate: {0}", alt.DescriptiveName));
alt.Items.Clear();
var secondParser = second.Count > 1 ? new AlternativeParser(second) : second[0];
if (first.Count > 0)
{
var firstParser = first.Count > 1 ? new AlternativeParser(first) : first[0];
var repeat = new RepeatParser(secondParser, 0)
{
Separator = separator
};
if (first.Count == 1 && first[0] == null)
{
alt.Items.Add(repeat);
}
else
{
alt.Items.Add(new SequenceParser(firstParser, repeat)
{
Separator = separator
});
}
}
else
{
alt.Items.Add(new RepeatParser(secondParser, 1)
{
Separator = separator
});
}
}
}
}
private bool Accept <TInput>(EmptyParser <TInput> p, BnfStringifyVisitor state)
{
state.Append("()");
return(true);
}
protected EmptyParser(EmptyParser other, ParserCloneArgs args)
: base(other, args)
{
}
