private void ExecuteRewriteForRule(InterpreterEvaluationTerm termToRewrite, TrsReductionRule rule, UnificationResult composedUnifier)
{
bool rewritingTookPlaceLocal = false;
if (composedUnifier.Succeed)
{
if (rule.Tail.GetType() == typeof(TrsNativeKeyword))
{
// Replacing term value with a native function generated value
var nativeTermInHead = ((TrsTermBase)termToRewrite.CurrentSubTerm.CreateCopy()).ApplySubstitutions(composedUnifier.Unifier);
foreach (var native in nativeFunctions)
{
var processedTerm = native.Evaluate(nativeTermInHead);
if (processedTerm == null)
{
throw new Exception(string.Format("Native function in type {0} returned null", native.GetType().FullName));
}
// If the rewrite result is the same, no rewriting took place ...
if (!nativeTermInHead.Equals(processedTerm))
{
var newTerm = termToRewrite.RootTerm.CreateCopyAndReplaceSubTerm(termToRewrite.CurrentSubTerm, processedTerm);
rewritingTookPlaceLocal = true;
var newTermWrapper = new InterpreterTerm(newTerm);
newTermWrapper.IsNewTerm = true;
executionCache.Add(newTermWrapper);
}
}
}
else
{
// Normal rewriting without native eval functions
var replacementTerm = ((TrsTermBase)rule.Tail.CreateCopy()).ApplySubstitutions(composedUnifier.Unifier);
if (!termToRewrite.CurrentSubTerm.Equals(replacementTerm))
{
var newTerm = termToRewrite.RootTerm.CreateCopyAndReplaceSubTerm(termToRewrite.CurrentSubTerm, replacementTerm);
rewritingTookPlaceLocal = true;
var newTermWrapper = new InterpreterTerm(newTerm);
newTermWrapper.IsNewTerm = true;
executionCache.Add(newTermWrapper);
}
}
}
if (rewritingTookPlaceLocal)
{
rewritingTookPlace = true; // stops rewriting on next rewrite step
termToRewrite.CacheSourceTerm.MustDeletFromCache = true;
}
}
private void ApplyReductionRuleToCache(TrsReductionRule rule)
{
// This data structure stores the Cartesian product used for term products
// The length of each sub-List is the size of an alphabet for calculating a "Godel string" of terms.
// This avoids the need for seperate sub-enumerators.
var rewriteCandidates = new List <List <InterpreterEvaluationTerm> >();
// Populate the rewriteCandidates
TrsTermProduct ruleHead = (TrsTermProduct)rule.Head;
int productLength = ruleHead.TermList.Count;
for (int termProductIndex = 0; termProductIndex < productLength; termProductIndex++)
{
rewriteCandidates.Add(new List <InterpreterEvaluationTerm>());
foreach (var termInCache in executionCache)
{
// Do not rewrite new terms, we are doing one rewrite step at a time
if (termInCache.IsNewTerm)
{
continue;
}
// Test all sub-terms
var expantionStack = new Stack <TrsTermBase>();
expantionStack.Push(termInCache.RootTerm);
while (expantionStack.Count > 0)
{
var current = expantionStack.Pop();
// Ignore the "variable only" case to avoid matching all rewrite rules to a sub-term.
if (current is TrsVariable)
{
continue;
}
// Type rules applied here ... cater for multiple unification results by duplicating candidates
foreach (var unifier in mguCalculation.GetUnifier(ruleHead.TermList[termProductIndex], current))
{
if (IsUnifierValid(unifier, ruleHead.TermList[termProductIndex]))
{
rewriteCandidates[termProductIndex].Add(new InterpreterEvaluationTerm(termInCache.RootTerm, current, termInCache, unifier));
}
}
// Apply rewrite rule to subterms
if (current is TrsTerm)
{
foreach (var subTerm in ((TrsTerm)current).Arguments)
{
expantionStack.Push(subTerm);
}
}
else if (current is TrsAcTerm)
{
foreach (var subTerm in ((TrsAcTerm)current).OnfArguments)
{
expantionStack.Push(subTerm.Term);
}
}
}
}
}
// Execute rewite step ... iterate over cartesian term product
// This iterationCount variable will prevent rewriting in the case where any of the lists are empty
int iterationCount = rewriteCandidates.First().Count;
foreach (var termList in rewriteCandidates.Skip(1))
{
iterationCount *= termList.Count;
}
var matchTupple = new List <InterpreterEvaluationTerm>(rewriteCandidates.Count);
for (int tuppleNumber = 0; tuppleNumber < iterationCount; tuppleNumber++)
{
var currDiv = tuppleNumber;
UnificationResult currentUnifier = null;
UnificationResult testUnifier = null;
matchTupple.Clear();
// In order to do a substitution, all variables must bind to the same values across the tupple members
for (int termColumn = 0; termColumn < rewriteCandidates.Count; termColumn++)
{
var currMod = currDiv % rewriteCandidates[termColumn].Count;
currDiv = currDiv / rewriteCandidates[termColumn].Count;
var targetTerm = rewriteCandidates[termColumn][currMod];
currentUnifier = targetTerm.Unifier;
if (testUnifier == null)
{
testUnifier = currentUnifier;
}
matchTupple.Add(targetTerm);
}
var termProductUnifier = ComposeUnifiers(matchTupple.Select(term => term.Unifier));
if (termProductUnifier.Succeed)
{
foreach (var term in matchTupple)
{
ExecuteRewriteForRule(term, rule, termProductUnifier);
}
}
}
}
