//*
// * 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 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);
}
//*
// * 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);
}
//*
// * Returns a look-ahead set with all conflics between
// * alternatives in a production pattern.
// *
// * @param pattern the production pattern
// * @param maxLength the maximum token sequence length
// *
// * @return a look-ahead set with the conflicts found
// *
// * @throws ParserCreationException if an inherent ambiguity was
// * found among the look-ahead sets
//
private LookAheadSet FindConflicts(ProductionPattern pattern, int maxLength)
{
LookAheadSet result = new LookAheadSet(maxLength);
LookAheadSet set1 = default(LookAheadSet);
LookAheadSet set2 = default(LookAheadSet);
for (int i = 0; i <= pattern.Count - 1; i++)
{
set1 = pattern[i].LookAhead;
for (int j = 0; j <= i - 1; j++)
{
set2 = pattern[j].LookAhead;
result.AddAll(set1.CreateIntersection(set2));
}
}
if (result.IsRepetitive())
{
ThrowAmbiguityException(pattern.Name, null, result);
}
return(result);
}
//*
// * Returns the union of all alternative look-ahead sets in a
// * production pattern.
// *
// * @param pattern the production pattern
// *
// * @return a unified look-ahead set
//
private LookAheadSet FindUnion(ProductionPattern pattern)
{
LookAheadSet result = default(LookAheadSet);
int length = 0;
int i = 0;
for (i = 0; i <= pattern.Count - 1; i++)
{
result = pattern[i].LookAhead;
if (result.GetMaxLength() > length)
{
length = result.GetMaxLength();
}
}
result = new LookAheadSet(length);
for (i = 0; i <= pattern.Count - 1; i++)
{
result.AddAll(pattern[i].LookAhead);
}
return(result);
}
//*
// * Creates a new look-ahead set that is the combination of
// * this set with another set. The combination is created by
// * creating new token sequences that consist of appending all
// * elements from the specified set onto all elements in this
// * set. This is sometimes referred to as the cartesian
// * product.
// *
// * @param set the set to combine with
// *
// * @return a new look-ahead set containing the combination
//
public LookAheadSet CreateCombination(LookAheadSet @set)
{
LookAheadSet result = new LookAheadSet(maxLength);
Sequence first = default(Sequence);
Sequence second = default(Sequence);
// Handle special cases
if (this.Size() <= 0)
{
return(@set);
}
else if (@set.Size() <= 0)
{
return(this);
}
for (int i = 0; i <= elements.Count - 1; i++)
{
// Create combinations
first = (Sequence)elements[i];
if (first.Length() >= maxLength)
{
result.Add(first);
}
else if (first.Length() <= 0)
{
result.AddAll(@set);
}
else
{
for (int j = 0; j <= @set.elements.Count - 1; j++)
{
second = (Sequence)@set.elements[j];
result.Add(first.Concat(maxLength, second));
}
}
}
return(result);
}
//*
// * Finds the look-ahead set for a production pattern. The 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 pattern the production pattern
// * @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 production pattern
// *
// * @throws ParserCreationException if an infinite loop was found
// * in the grammar
//
private LookAheadSet FindLookAhead(ProductionPattern pattern, int length, CallStack stack, LookAheadSet filter)
{
LookAheadSet result = default(LookAheadSet);
LookAheadSet temp = default(LookAheadSet);
// Check for infinite loop
if (stack.Contains(pattern.Name, length))
{
throw new ParserCreationException(ParserCreationException.ErrorType.INFINITE_LOOP, pattern.Name, (string)null);
}
// Find pattern look-ahead
stack.Push(pattern.Name, length);
result = new LookAheadSet(length);
for (int i = 0; i <= pattern.Count - 1; i++)
{
temp = FindLookAhead(pattern[i], length, 0, stack, filter);
result.AddAll(temp);
}
stack.Pop();
return(result);
}
//*
// * Calculates the look-ahead needed for the specified production
// * pattern. This method attempts to resolve any conflicts and
// * stores the results in the pattern look-ahead object.
// *
// * @param pattern the production pattern
// *
// * @throws ParserCreationException if the look-ahead set couldn't
// * be determined due to inherent ambiguities
//
private void CalculateLookAhead(ProductionPattern pattern)
{
ProductionPatternAlternative alt = default(ProductionPatternAlternative);
LookAheadSet result = default(LookAheadSet);
LookAheadSet[] alternatives = null;
LookAheadSet conflicts = default(LookAheadSet);
LookAheadSet previous = new LookAheadSet(0);
int length = 1;
int i = 0;
CallStack stack = new CallStack();
// Calculate simple look-ahead
stack.Push(pattern.Name, 1);
result = new LookAheadSet(1);
alternatives = new LookAheadSet[pattern.Count];
for (i = 0; i <= pattern.Count - 1; i++)
{
alt = pattern[i];
alternatives[i] = FindLookAhead(alt, 1, 0, stack, null);
alt.LookAhead = alternatives[i];
result.AddAll(alternatives[i]);
}
if (pattern.LookAhead == null)
{
pattern.LookAhead = result;
}
conflicts = FindConflicts(pattern, 1);
// Resolve conflicts
while (conflicts.Size() > 0)
{
length += 1;
stack.Clear();
stack.Push(pattern.Name, length);
conflicts.AddAll(previous);
for (i = 0; i <= pattern.Count - 1; i++)
{
alt = pattern[i];
if (alternatives[i].Intersects(conflicts))
{
alternatives[i] = FindLookAhead(alt, length, 0, stack, conflicts);
alt.LookAhead = alternatives[i];
}
if (alternatives[i].Intersects(conflicts))
{
if (pattern.DefaultAlternative == null)
{
pattern.DefaultAlternative = alt;
}
else if (!object.ReferenceEquals(pattern.DefaultAlternative, alt))
{
result = alternatives[i].CreateIntersection(conflicts);
ThrowAmbiguityException(pattern.Name, null, result);
}
}
}
previous = conflicts;
conflicts = FindConflicts(pattern, length);
}
for (i = 0; i <= pattern.Count - 1; i++)
{
// Resolve conflicts inside rules
CalculateLookAhead(pattern[i], 0);
}
}