//*
// * Calculates the look-aheads needed for the specified pattern
// * alternative. This method attempts to resolve any conflicts in
// * optional elements by recalculating look-aheads for referenced
// * productions.
// *
// * @param alt the production pattern alternative
// * @param pos the pattern element position
// *
// * @throws ParserCreationException if the look-ahead set couldn't
// * be determined due to inherent ambiguities
//
private void CalculateLookAhead(ProductionPatternAlternative alt, int pos)
{
ProductionPattern pattern = default(ProductionPattern);
ProductionPatternElement elem = default(ProductionPatternElement);
LookAheadSet first = default(LookAheadSet);
LookAheadSet follow = default(LookAheadSet);
LookAheadSet conflicts = default(LookAheadSet);
LookAheadSet previous = new LookAheadSet(0);
string location = null;
int length = 1;
// Check trivial cases
if (pos >= alt.Count)
{
return;
}
// Check for non-optional element
pattern = alt.Pattern;
elem = alt[pos];
if (elem.MinCount == elem.MaxCount)
{
CalculateLookAhead(alt, pos + 1);
return;
}
// Calculate simple look-aheads
first = FindLookAhead(elem, 1, new CallStack(), null);
follow = FindLookAhead(alt, 1, pos + 1, new CallStack(), null);
// Resolve conflicts
location = "at position " + (pos + 1);
conflicts = FindConflicts(pattern.Name, location, first, follow);
while (conflicts.Size() > 0)
{
length += 1;
conflicts.AddAll(previous);
first = FindLookAhead(elem, length, new CallStack(), conflicts);
follow = FindLookAhead(alt, length, pos + 1, new CallStack(), conflicts);
first = first.CreateCombination(follow);
elem.LookAhead = first;
if (first.Intersects(conflicts))
{
first = first.CreateIntersection(conflicts);
ThrowAmbiguityException(pattern.Name, location, first);
}
previous = conflicts;
conflicts = FindConflicts(pattern.Name, location, first, follow);
}
// Check remaining elements
CalculateLookAhead(alt, pos + 1);
}
//*
// * Finds the look-ahead set for a production pattern alternative.
// * The pattern position and maximum look-ahead length must be
// * specified. It is also possible to specify a look-ahead set
// * filter, which will make sure that unnecessary token sequences
// * will be avoided.
// *
// * @param alt the production pattern alternative
// * @param length the maximum look-ahead length
// * @param pos the pattern element position
// * @param stack the call stack used for loop detection
// * @param filter the look-ahead set filter
// *
// * @return the look-ahead set for the pattern alternative
// *
// * @throws ParserCreationException if an infinite loop was found
// * in the grammar
//
private LookAheadSet FindLookAhead(ProductionPatternAlternative alt, int length, int pos, CallStack stack, LookAheadSet filter)
{
LookAheadSet first = default(LookAheadSet);
LookAheadSet follow = default(LookAheadSet);
LookAheadSet overlaps = default(LookAheadSet);
// Check trivial cases
if (length <= 0 || pos >= alt.Count)
{
return(new LookAheadSet(0));
}
// Find look-ahead for this element
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))
{
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);
}
//*
// * Finds the look-ahead set for a production pattern element. The
// * maximum look-ahead length must be specified. This method takes
// * the element repeats into consideration when creating the
// * look-ahead set, but does NOT include an empty sequence even if
// * the minimum count is zero (0). It is also possible to specify a
// * look-ahead set filter, which will make sure that unnecessary
// * token sequences will be avoided.
// *
// * @param elem the production pattern element
// * @param length the maximum look-ahead length
// * @param stack the call stack used for loop detection
// * @param filter the look-ahead set filter
// *
// * @return the look-ahead set for the pattern element
// *
// * @throws ParserCreationException if an infinite loop was found
// * in the grammar
//
private LookAheadSet FindLookAhead(ProductionPatternElement elem, int length, CallStack stack, LookAheadSet filter)
{
LookAheadSet result = default(LookAheadSet);
LookAheadSet first = default(LookAheadSet);
LookAheadSet follow = default(LookAheadSet);
int max = 0;
// Find initial element look-ahead
first = FindLookAhead(elem, length, 0, stack, filter);
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();
}
max = elem.MaxCount;
if (length < max)
{
max = length;
}
for (int i = 1; i <= max - 1; i++)
{
first = first.CreateOverlaps(filter);
if (first.Size() <= 0 || first.GetMinLength() >= length)
{
break; // TODO: might not be correct. Was : Exit For
}
follow = FindLookAhead(elem, length, 0, stack, filter.CreateFilter(first));
first = first.CreateCombination(follow);
result.AddAll(first);
}
return(result);
}