private AltLoopStatus TryOneAlternative(int ip, VarStack varStack, ListPatternElem e, int k,
int marker, ListTerm RangeList, int i, BaseTerm t, ref bool negSearchSucceeded, BaseTerm searchTerm)
{
bool unified = searchTerm.Unify(t, varStack);
if (e.IsNegSearch) // none of the terms in the inner loop may match. ~(a | b | c) = ~a & ~b & ~c
{
if (unified) // ... no point in investigating the other alternatives if one does
{
negSearchSucceeded = false;
return(AltLoopStatus.Break); // don't try the other alternatives
}
return(AltLoopStatus.TryNextDown); // non of the downranges matches may lead to a success
}
else
{
if (unified && // we found a match. Unify, and
TryBindingAltListVarToMatch(e.AltListBindVar, t, varStack) && // bind the AltListBindVar to the match
TryBindingRangeRelatedVars(e, i, RangeList, varStack)) // bind the range to the range variables
{
if (ip == pattern.Length - 1) // this was the last pattern element
{
if (k == target.Count - 1) // both pattern and target exhausted
{
return(AltLoopStatus.MatchFound);
}
}
else if (UnifyTailEx(ip + 1, k + 1, varStack)) // now deal with the rest
{
return(AltLoopStatus.MatchFound);
}
}
// if we arrive here, it was not possible to ...
// (1) ... unify the range's SearchTerm with the target element, or
// (2) ... unify the range variable with the range list, or
// (3) ... successfully process the rest of the pattern and target
// Now unbind and try matching with the next target element
BaseTerm.UnbindToMarker(varStack, marker);
return(AltLoopStatus.TryNextDown); // try the next downrange match
}
}
// each call processes one element of pattern[]
bool UnifyTailEx(int ip, int it, VarStack varStack)
{
ListPatternElem e = (ListPatternElem)pattern[ip];
Variable rangeSpecVar = (Variable)e.RangeBindVar;
NodeIterator subtreeIterator;
int k;
int marker;
ListTerm RangeList = null;
BaseTerm tail = null;
int minLen; // minimum required range length (number of range elements)
int maxLen; // maximum possible ...
if (!DoLowerAndUpperboundChecks(ip, it, out minLen, out maxLen))
{
return(false);
}
// scan the minimal number of range elements. Add them to the range list,
// i.e. the last variable (if present) preceding the '{ , }'
for (int i = 0; i < minLen; i++)
{
if ((k = it + i) >= target.Count)
{
return(false);
}
AppendToRangeList(ref RangeList, rangeSpecVar, target[k], ref tail);
}
marker = varStack.Count; // register the point to which we must possibly undo unifications
if (e.HasSearchTerm)
{
// scan the elements up to the maximum range length, and the element immediately thereafter
for (int i = minLen; i <= maxLen; i++)
{
BaseTerm t = null;
k = it + i;
if (k == target.Count)
{
return(false);
}
bool negSearchSucceeded = true; // iff none of the alternative term matches the target term
for (int j = 4; j < e.Args.Length; j++) // scan all AltSearchTerm alternatives (separated by '|')
{
BaseTerm searchTerm = e.AltSearchTerms[j];
DownRepFactor downRepFactor = null; // e.downRepFactor [j];
t = target[k];
AltLoopStatus status = AltLoopStatus.TryNextAlt;
if (downRepFactor == null)
{
status =
TryOneAlternative(ip, varStack, e, k, marker, RangeList, i, t, ref negSearchSucceeded, searchTerm);
if (status == AltLoopStatus.MatchFound)
{
return(true);
}
}
else // traverse the downRepFactor tree, which in principle may yield more than one match
{
subtreeIterator = new NodeIterator(t, searchTerm, downRepFactor.minLenTerm,
downRepFactor.maxLenTerm, false, downRepFactor.bindVar, varStack);
foreach (BaseTerm match in subtreeIterator) // try -- if necessary -- each tree match with the current search term
{
status =
TryOneAlternative(ip, varStack, e, k, marker, RangeList, i, match, ref negSearchSucceeded, searchTerm);
if (status == AltLoopStatus.MatchFound)
{
return(true);
}
if (status == AltLoopStatus.Break)
{
break;
}
}
}
if (status == AltLoopStatus.Break)
{
break;
}
}
// at this point sufficient alternatives have been tried
if (e.IsNegSearch && negSearchSucceeded) // none of the terms matched => ok if binding succeeds
{
if (!TryBindingAltListVarToMatch(e.AltListBindVar, t, varStack) || // bind the AltListBindVar to the match
!TryBindingRangeRelatedVars(e, i, RangeList, varStack)) // bind the range to the range variables
{
return(false); // binding failed
}
if (ip == pattern.Length - 1) // this was the last pattern element
{
if (k == target.Count - 1) // both pattern and target exhausted
{
return(true);
}
}
else if (UnifyTailEx(ip + 1, k + 1, varStack)) // now deal with the rest
{
return(true);
}
}
else if (i < maxLen) // append the rejected term to the range list and go try the next term
{
AppendToRangeList(ref RangeList, rangeSpecVar, t, ref tail);
}
}
}
else // a range without a subsequent search term (so followed by another range or end of pattern)
{
for (int i = minLen; i <= maxLen; i++)
{
k = it + i;
if (k == target.Count) // ok, target[k] does not exist, end of target hit
{
return(TryBindingRangeRelatedVars(e, i, RangeList, varStack)); // i is actual range length
}
// k is ok
if (i < maxLen)
{
AppendToRangeList(ref RangeList, rangeSpecVar, target[k], ref tail);
}
// now deal with the rest
if (TryBindingRangeRelatedVars(e, i, RangeList, varStack) &&
UnifyTailEx(ip + 1, k, varStack))
{
return(true);
}
}
}
// If we arrive here, no matching term was found in or immediately after the permitted range.
// Therefore, undo any unifications made locally in this method and return with failure.
if (marker != 0)
{
BaseTerm.UnbindToMarker(varStack, marker);
}
return(false);
}