// ______________
// return <value>
private GrammarReturn ParseReturn(ref LexerStringReader reader)
{
reader.MoveBy(Return.Length);
var nonTerminalName = new string(reader.ReadTillEndOfWord());
if (_nonTerminals.TryGetValue(nonTerminalName, out var grammarElement) == false)
{
throw new GrammarParserException($"Non-terminal {nonTerminalName} does not exist.");
}
return(new GrammarReturn(new GrammarNonTerminalUsage(grammarElement.Name, grammarElement)));
}
private GrammarReturn ParseImpl()
{
GrammarReturn final = null;
var reader = new LexerStringReader(_grammar, 0);
while (reader.IsInRange())
{
if (reader.IsEndOfLine())
{
reader.MoveNext();
continue;
}
if (reader.StartsWith(Comment.AsSpan()))
{
reader.MoveToNextLine();
continue;
}
reader.ReadTillEndOfWhitespace();
if (reader.StartsWith(GrammarNonTerminalStart.ToString().AsSpan()))
{
// _______________________________________
// <value> : Literal|<function-invokation>
var nonTerminalName = new string(reader.ReadTillEndOfWord()); // <value>
if (nonTerminalName.EndsWith(GrammarNonTerminalEnd) == false)
{
throw new GrammarParserException($"Non-terminal {nonTerminalName} name " +
$"should finish with {GrammarNonTerminalEnd}");
}
var nonTerminal = GetNonTerminalByName(nonTerminalName);
if (nonTerminal.FullyParsed)
{
throw new GrammarParserException($"Cannot declare {nonTerminalName} more than once.");
}
// skip ':'
var assign = new string(reader.ReadWhile(x => x != Assign)) + reader.CurrentChar;
if (assign.EndsWith(Assign) == false)
{
throw new GrammarParserException($"Invalid syntax for {nonTerminalName}.");
}
reader.MoveNext();
reader.ReadTillEndOfWhitespace();
nonTerminal.Body = ParseNonTerminalBody(ref reader, nonTerminal);
continue;
}
if (reader.StartsWith(Return.AsSpan()))
{
final = ParseReturn(ref reader);
break;
}
throw new GrammarParserException($"Invalid grammar syntax. Line: {new string(reader.ReadTillNewLine())}");
}
if (final == null)
{
throw new GrammarParserException("Return statement not found.");
}
var notExistingNonTerminal = _nonTerminals.Select(x => x.Value).FirstOrDefault(x => x.FullyParsed == false);
if (notExistingNonTerminal != null)
{
throw new GrammarParserException($"Non-terminal '{notExistingNonTerminal.Name}' " +
"is not declared. Are you sure your gramma is fine?");
}
foreach (var nonTerminal in _nonTerminals.Select(x => x.Value))
{
if (nonTerminal.Body.OrConditionOperands.All(x => x.IsRecursive))
{
var msg = $"Infinite recursion detected in {nonTerminal.Name} non-terminal. " +
"Use '|' to create escape path.";
throw new GrammarParserException(msg);
}
}
return(final);
}