public override Term ApplySubstitution(Substitution sigma)
{
// Does sigma apply to our variable?
Term replacement = sigma.GetMapping(this);
if (replacement == null)
return this; // nothing to change!
// Otherwise, return the variable's replacement
return replacement;
}
public override bool Mgu(Term t, Substitution subsSoFar)
{
if (t is TermObject)
{
Term replacement = subsSoFar.GetMapping(this);
if (replacement != null)
{
TermVariable termVariable = replacement as TermVariable;
if (termVariable != null)
{
subsSoFar.AddMapping(this, t);
subsSoFar.AddMapping(termVariable, t);
return true;
}
return replacement.Equals(t);
}
// There was no replacement:
// Add a mapping for the variable to this term-object
subsSoFar.AddMapping(this, t);
return true;
}
var variable = t as TermVariable;
if (variable != null)
{
TermVariable it = variable;
Term myReplacement = subsSoFar.GetMapping(this);
Term itsReplacement = subsSoFar.GetMapping(it);
if (itsReplacement == null)
{
// just map 'it' to me (or my replacement)
if (myReplacement == null)
{
if (!Equals(it))
subsSoFar.AddMapping(it, this);
}
else
{
if (!(myReplacement is TermVariable) || !myReplacement.Equals(it))
subsSoFar.AddMapping(it, myReplacement);
}
return true;
}
// At this point, 'it' has a replacement.
if (myReplacement == null)
{
// I don't have a replacement, so map me to it, or to its replacement
if (!(itsReplacement is TermVariable) || !itsReplacement.Equals(this))
subsSoFar.AddMapping(this, itsReplacement);
return true;
}
// At this point, both term variables have replacements.
// So make sure that they are the same!
return myReplacement.Equals(itsReplacement);
}
var func = t as TermFunction;
if (func != null)
{
Term myReplacement = subsSoFar.GetMapping(this);
// Case 1: I have a replacement
if (myReplacement != null)
// See if my replacement can be unified with the function
return myReplacement.Mgu(func, subsSoFar);
// Case 2: I have no replacement
TermFunction itsReplacement = subsSoFar.GetMapping(func);
if (itsReplacement.HasVariable(this))
return false;
// just set my replacement to the function
subsSoFar.AddMapping(this, itsReplacement);
return true;
}
throw new Exception("TermVariable.mgu: Don't know how to handle term of type " + t.GetType().Name);
}
protected bool Equals(Substitution other)
{
if (other.NumMappings() != NumMappings())
return false;
List<TermVariable> subs = Substitutions.Keys.ToList();
//this cannot be a foreach as GetMapping possibly modifies the collection
for (int i = 0; i < subs.Count; i++)
{
TermVariable currrentKey = subs[i];
if (!GetMapping(currrentKey).Equals(other.GetMapping(currrentKey)))
return false;
}
return true;
//return other.NumMappings() == NumMappings() && _substitutions.All(kv => GetMapping(kv.Key).Equals(other.GetMapping(kv.Key)));
}
