public void IsNullableTest()
{
var grammar = new Grammar();
var S = grammar.Symbols.Add("S");
var a = grammar.Symbols.Add("a");
var b = grammar.Symbols.Add("b");
var A = grammar.Symbols.Add("A");
var B = grammar.Symbols.Add("B");
grammar.Start = S;
grammar.Productions.Define(S, new[] { b, A });
grammar.Productions.Define(A, new[] { a, A, B });
grammar.Productions.Define(A, new Symbol[0]);
grammar.Productions.Define(B, new Symbol[0]);
var target = new RuntimeGrammar(grammar);
Assert.IsTrue(target.IsNullable(A.Index));
Assert.IsTrue(target.IsNullable(B.Index));
Assert.IsFalse(target.IsNullable(a.Index));
Assert.IsFalse(target.IsNullable(b.Index));
Assert.IsFalse(target.IsNullable(S.Index));
}
private void BuildCache()
{
int tokenCount = grammar.SymbolCount;
tokenCache = new SppfNode[tokenCount];
for (int token = 0; token != tokenCount; ++token)
{
if (grammar.IsNullable(token))
{
tokenCache[token] = new SppfNode(token, null, Loc.Unknown, HLoc.Unknown);
}
}
ruleOffsetInCache = new int[grammar.Productions.Count];
ruleEndOffsetInCache = new int[grammar.Productions.Count];
int nullableCount = 0;
foreach (var rule in grammar.Productions)
{
int i = rule.PatternTokens.Length;
while (i != 0)
{
int token = rule.PatternTokens[--i];
if (tokenCache[token] == null)
{
break;
}
++nullableCount;
}
ruleEndOffsetInCache[rule.Index] = nullableCount;
ruleOffsetInCache[rule.Index] = nullableCount - rule.PatternTokens.Length;
}
this.ruleCache = new SppfNode[nullableCount];
foreach (var rule in grammar.Productions)
{
int endOffset = ruleOffsetInCache[rule.Index] + rule.PatternTokens.Length;
int i = rule.PatternTokens.Length;
while (i != 0)
{
int token = rule.PatternTokens[--i];
if (tokenCache[token] == null)
{
break;
}
ruleCache[--endOffset] = tokenCache[token];
}
}
}
private Msg InternalGetNullable(int nonTerm, IStackLookback <Msg> stackLookback)
{
Debug.Assert(grammar.IsNullable(nonTerm));
var production =
(from r in grammar.GetProductions(nonTerm)
where r.PatternTokens.All(grammar.IsNullable)
orderby r.PatternTokens.Length ascending
select r)
.First();
var args = new Msg[production.PatternTokens.Length];
for (int i = 0; i != args.Length; ++i)
{
args[i] = InternalGetNullable(production.PatternTokens[i], stackLookback);
}
var value = productionAction(production.Index, args, 0, context, stackLookback);
return(new Msg(nonTerm, value, Loc.Unknown));
}