private static void DCGGoal(Term t, ref TermNode body, ref Term remainder, ref bool embedded)
{
Term temp;
if (t.IsString || t is Cut)
body.Append(t);
else if (t.Functor == Parser.CURL)
{
while (t.Arity == 2)
{
body.Append(t.Arg(0));
t = t.Arg(1);
embedded = true;
}
}
else if (t.IsList)
{
temp = new Term();
if (t == NULLLIST) t = temp; else t.SetRightmostArg(temp);
if (embedded)
{
body.Append(new Term(Parser.EQ, remainder, t, FType.comp, OType.xfx, 700));
embedded = false;
}
else
remainder.Bind(t); // in this case, nothing is appended to body, which may be left empty (e.g. t-->[x])
remainder = temp;
}
else if (t.IsAtom || t.IsCompound)
{
t = new DCGTerm(t, ref remainder);
body.Append(t);
}
else if (t.IsVar)
PrologIO.Error("Variable not allowed in DCG-clause: {0}", t.VarName());
else
PrologIO.Error("Illegal term in DCG-clause: {0}", t);
}
private void DCGBracketList(TerminalSet _TS, out Term term)
{
Term head;
ArrayList elements = null;
GetSymbol(new TerminalSet(LCuBracket), true, true);
GetSymbol(new TerminalSet(LeftParen, Identifier, IntLiteral, RealLiteral, StringLiteral, Operator, Atom, Anonymous,
CutSym, LSqBracket, LCuBracket, RCuBracket, PrologString), false, true);
if (symbol.IsMemberOf(LeftParen, Identifier, IntLiteral, RealLiteral, StringLiteral, Operator, Atom, Anonymous, CutSym,
LSqBracket, LCuBracket, PrologString))
{
PrologTerm(new TerminalSet(RCuBracket), out head);
elements = head.ArgumentsToArrayList(true);
}
GetSymbol(new TerminalSet(RCuBracket), true, true);
term = new DCGTerm();
if (elements != null)
for (int i = elements.Count - 1; i >= 0; i--) term = new DCGTerm((Term)elements[i], term);
}
// DCG stuff
public TermNode ToDCG(ref Term lhs) // cf. Side Notes SN3
{
TermNode body = new TermNode();
Term result = null;
Term inVar = new Term();
Term inVarSave = inVar;
Term outVar = inVar;
lhs = new DCGTerm(lhs, ref outVar); // outVar becomes new term
Term remainder;
try
{
readingDCGClause = true;
ArrayList alternatives = AlternativesToArrayList();
for (int i = 0; i < alternatives.Count; i++)
{
Term alt = (Term)alternatives[i];
bool embedded = (alternatives.Count > 1);
ArrayList terms = alt.ArgumentsToArrayList(true); // flatten clause such as X --> (A, B), C.
body.Clear();
remainder = inVarSave;
for (int ii = 0; ii < terms.Count; ii++)
DCGGoal((Term)terms[ii], ref body, ref remainder, ref embedded);
// create a term-tree from the array
if (i == 0)
result = TermSeq(body);
else
result = new Term(Parser.SEMI, result, TermSeq(body), FType.comp, OType.xfy, 1100);
remainder.Bind(outVar);
}
}
finally
{
readingDCGClause = false;
}
return (result == null) ? null : result.ToGoalList(); // empty body treated similar to null
}