public bool MoveNext(
EquivalenceRelation <StdTerm> eqs,
Map <StdTerm, bool> history,
out StdTerm u,
out bool violated)
{
bool isVisited;
while (freeOccIt.MoveNext())
{
u = eqs.GetRepresentative(freeOccIt.Current);
if (history.TryFindValue(u, out isVisited))
{
if (!isVisited)
{
violated = true;
return(false);
}
continue;
}
violated = false;
return(true);
}
u = default(StdTerm);
violated = false;
return(false);
}
private static void RegisterSelectors(Set <StdTerm> allVars, EquivalenceRelation <StdTerm> eqs, StdTerm stdterm)
{
var index = stdterm.term.Owner;
var t = stdterm.term;
eqs.Add(stdterm);
while (t.Symbol == index.SelectorSymbol)
{
eqs.AddToTrackSet(
t.Args[0].Standardize(stdterm.label),
Track_FreeOccurs,
t.Standardize(stdterm.label));
t = t.Args[0];
}
Contract.Assert(t.Symbol.IsVariable);
allVars.Add(t.Standardize(stdterm.label));
}
private static void Bind(
Set <StdTerm> allVars,
EquivalenceRelation <StdTerm> eqs,
Stack <Tuple <StdTerm, StdTerm> > pending,
StdTerm bindee,
StdTerm binding)
{
if (eqs.Equals(bindee, binding))
{
return;
}
var index = bindee.term.Owner;
Contract.Assert(bindee.term.Symbol == index.SelectorSymbol || bindee.term.Symbol.IsVariable);
Contract.Assert(binding.term.Symbol == index.SelectorSymbol || binding.term.Symbol.IsVariable || binding.term.Symbol.IsDataConstructor || binding.term.Symbol.IsNonVarConstant);
RegisterSelectors(allVars, eqs, bindee);
if (binding.term.Symbol.IsDataConstructor || binding.term.Symbol.IsNonVarConstant)
{
var crntBinding = eqs.SetTracker(bindee, Track_FreeApply, binding);
if (StdTerm.Compare(crntBinding, binding) != 0)
{
pending.Push(new Tuple <StdTerm, StdTerm>(crntBinding, binding));
}
binding.term.Visit(
x => x.Groundness == Groundness.Variable && x.Symbol.IsDataConstructor ? x.Args : null,
x =>
{
if (x.Symbol.IsVariable || x.Symbol == index.SelectorSymbol)
{
RegisterSelectors(allVars, eqs, x.Standardize(binding.label));
eqs.AddToTrackSet(bindee, Track_FreeOccurs, x.Standardize(binding.label));
}
});
}
else
{
RegisterSelectors(allVars, eqs, binding);
}
eqs.Equate(bindee, binding);
}
private static bool OccursCheck(Set <StdTerm> vars, EquivalenceRelation <StdTerm> eqs)
{
//// History[v] is false if the occurs check is visiting v.
//// History[v] is true if the occurs check visited v and did not find violations.
var history = new Map <StdTerm, bool>(StdTerm.Compare);
var stack = new Stack <OccursState>();
StdTerm u, rep;
OccursState top;
bool isVisited, violated;
foreach (var v in vars)
{
rep = eqs.GetRepresentative(v);
if (history.TryFindValue(rep, out isVisited))
{
Contract.Assert(isVisited);
continue;
}
stack.Push(new OccursState(rep, history, eqs));
while (stack.Count > 0)
{
top = stack.Peek();
if (top.MoveNext(eqs, history, out u, out violated))
{
stack.Push(new OccursState(u, history, eqs));
}
else if (violated)
{
return(false);
}
else
{
stack.Pop().Finished(history);
}
}
}
return(true);
}
public OccursState(StdTerm rep, Map <StdTerm, bool> history, EquivalenceRelation <StdTerm> eqs)
{
this.rep = rep;
this.freeOccIt = eqs.GetTrackSet(rep, Track_FreeOccurs).GetEnumerator();
history.Add(rep, false);
}
public static bool IsUnifiable(Term tA, Term tB, bool standardize = true)
{
Contract.Requires(tA != null && tB != null);
Contract.Requires(tA.Owner == tB.Owner);
var eqs = new EquivalenceRelation <StdTerm>(StdTerm.Compare, 1, 1);
var success = new SuccessToken();
var relabelSymbol = tA.Owner.SymbolTable.GetOpSymbol(ReservedOpKind.Relabel);
var pending = new Stack <Tuple <StdTerm, StdTerm> >();
pending.Push(new Tuple <StdTerm, StdTerm>(tA.Standardize(0), tB.Standardize(standardize ? 1 : 0)));
int lblA, lblB;
Term trmA, trmB;
Tuple <StdTerm, StdTerm> top;
Set <StdTerm> allVars = new Set <StdTerm>(StdTerm.Compare);
while (pending.Count > 0)
{
top = pending.Pop();
if (StdTerm.Compare(top.Item1, top.Item2) == 0)
{
continue;
}
top.GetComponents(out trmA, out lblA, out trmB, out lblB);
trmA.Compute <Unit>(
trmB,
(xA, xB, s) =>
{
if (xA.Symbol == relabelSymbol)
{
xA = EliminateRelabel(xA);
}
if (xB.Symbol == relabelSymbol)
{
xB = EliminateRelabel(xB);
}
if (xA.Groundness == Groundness.Ground && xB.Groundness == Groundness.Ground)
{
//// If x1 and x2 are ground, then just check equality.
if (xA != xB)
{
success.Failed();
}
return(null);
}
else if ((xA.Symbol.IsDataConstructor || xA.Symbol.IsNonVarConstant) &&
(xB.Symbol.IsDataConstructor || xB.Symbol.IsNonVarConstant))
{
//// If x1 and x2 are both data constructors,
//// then check symbol equality and unroll.
if (xA.Symbol != xB.Symbol)
{
success.Failed();
return(null);
}
return(new Tuple <IEnumerable <Term>, IEnumerable <Term> >(xA.Args, xB.Args));
}
else if (xA.Symbol.IsVariable || xA.Symbol == xA.Owner.SelectorSymbol)
{
Bind(allVars, eqs, pending, xA.Standardize(lblA), xB.Standardize(lblB));
return(null);
}
else
{
Bind(allVars, eqs, pending, xB.Standardize(lblB), xA.Standardize(lblA));
return(null);
}
},
(xA, xB, ch, s) =>
{
return(default(Unit));
},
success);
}
if (!success.Result)
{
return(false);
}
return(OccursCheck(allVars, eqs));
}
private static Term MkMGU(StdTerm t, EquivalenceRelation <StdTerm> eqs, Func <int, Term> varCreator)
{
Term normVar;
StdTerm stdRep, stdX;
int i, label;
bool wasAdded;
var varMap = new Map <StdTerm, Term>(StdTerm.Compare);
var labelStack = new Stack <int>();
labelStack.Push(t.label);
var result = t.term.Compute <Term>(
(x, s) =>
{
if (x.Groundness == Groundness.Ground)
{
labelStack.Push(labelStack.Peek());
return(null);
}
else if (!x.Symbol.IsVariable)
{
labelStack.Push(labelStack.Peek());
return(x.Args);
}
stdX = x.Standardize(labelStack.Peek());
if (eqs.GetTracker(stdX, Track_FreeApply, out stdRep))
{
labelStack.Push(stdRep.label);
return(EnumerableMethods.GetEnumerable <Term>(stdRep.term));
}
else if (StdTerm.Compare(stdRep = eqs.GetRepresentative(stdX), stdX) == 0)
{
labelStack.Push(labelStack.Peek());
return(null);
}
else
{
labelStack.Push(stdRep.label);
return(EnumerableMethods.GetEnumerable <Term>(stdRep.term));
}
},
(x, c, s) =>
{
label = labelStack.Pop();
if (x.Groundness == Groundness.Ground)
{
return(x);
}
else if (!x.Symbol.IsVariable)
{
i = 0;
var args = new Term[x.Symbol.Arity];
foreach (var tp in c)
{
args[i++] = tp;
}
return(x.Owner.MkApply(x.Symbol, args, out wasAdded));
}
if (c.IsEmpty <Term>())
{
if (!varMap.TryFindValue(x.Standardize(label), out normVar))
{
normVar = varCreator(varMap.Count);
varMap.Add(x.Standardize(label), normVar);
}
return(normVar);
}
else
{
return(c.First <Term>());
}
});
Contract.Assert(labelStack.Count == 1);
return(result);
}
