private LookAheadSet FindLookAhead(ProductionPatternElement elem,
int length,
CallStack stack,
LookAheadSet filter)
{
// Find initial element look-ahead
var first = FindLookAhead(elem, length, 0, stack, filter);
var result = new LookAheadSet(length);
result.AddAll(first);
if (filter == null || !filter.IsOverlap(result))
{
return(result);
}
// Handle element repetitions
if (elem.MaxCount == Int32.MaxValue)
{
first = first.CreateRepetitive();
}
var max = elem.MaxCount;
if (length < max)
{
max = length;
}
for (int i = 1; i < max; i++)
{
first = first.CreateOverlaps(filter);
if (first.Size() <= 0 || first.GetMinLength() >= length)
{
break;
}
var follow = FindLookAhead(elem,
length,
0,
stack,
filter.CreateFilter(first));
first = first.CreateCombination(follow);
result.AddAll(first);
}
return(result);
}
private LookAheadSet FindLookAhead(ProductionPatternAlternative alt,
int length,
int pos,
CallStack stack,
LookAheadSet filter)
{
LookAheadSet follow;
// Check trivial cases
if (length <= 0 || pos >= alt.Count)
{
return(new LookAheadSet(0));
}
// Find look-ahead for this element
var first = FindLookAhead(alt[pos], length, stack, filter);
if (alt[pos].MinCount == 0)
{
first.AddEmpty();
}
// Find remaining look-ahead
if (filter == null)
{
length -= first.GetMinLength();
if (length > 0)
{
follow = FindLookAhead(alt, length, pos + 1, stack, null);
first = first.CreateCombination(follow);
}
}
else if (filter.IsOverlap(first))
{
var overlaps = first.CreateOverlaps(filter);
length -= overlaps.GetMinLength();
filter = filter.CreateFilter(overlaps);
follow = FindLookAhead(alt, length, pos + 1, stack, filter);
first.RemoveAll(overlaps);
first.AddAll(overlaps.CreateCombination(follow));
}
return(first);
}