static Nonterminal Reduce(ParserStack stack, RuleType rule)
{
// Create a language element array big enough to hold the LHS and RHS
// arguments.
//
var parameterCount = 1 + rule.Rhs.Length;
var parameters = new LanguageElement[parameterCount];
// Create the LHS nonterminal.
//
var lhs = rule.Lhs.CreateNonterminal();
parameters[0] = lhs;
// Pop the RHS language elements off the stack.
//
for (var idx = 0; idx < rule.Rhs.Length; ++idx)
{
parameters[parameterCount - idx - 1] = stack.Pop().LanguageElement;
}
// Invoke the rule.
//
rule.Invoke(parameters);
return(lhs);
}
/// <summary>
/// Performs syntax analysis against a sequence of terminals according to the <see cref="Grammar"/> used to create the <see cref="Parser"/>.
/// </summary>
/// <param name="terminalReader">Retrieves a sequence of <see cref="Terminal"/> objects.</param>
/// <returns>If syntax analysis succeeds, returns the <see cref="Nonterminal"/> associated with <see cref="Grammar.StartNonterminal"/>. Otherwise, <value>null</value> is returned.</returns>
public Nonterminal Parse(ITerminalReader terminalReader)
{
var stack = new ParserStack();
stack.Push(null, InitialState);
var terminal = terminalReader.ReadTerminal();
while (terminal != null)
{
if (terminal.ElementType.Ignore)
{
terminal = terminalReader.ReadTerminal();
}
else
{
var action = stack.Peek().State.GetAction(terminal.ElementType);
LinguaTrace.TraceEvent(TraceEventType.Information, LinguaTraceId.ID_PARSE_ACTION, "{0}", action);
if (action == null)
{
return(null);
}
switch (action.ActionType)
{
case ParserActionTypes.Accept:
{
var reduce = (ParserActionAccept)action;
var rule = reduce.Rule;
var lhs = Reduce(stack, rule);
return(lhs);
}
case ParserActionTypes.Shift:
{
var shift = (ParserActionShift)action;
stack.Push(terminal, shift.State);
terminal = terminalReader.ReadTerminal();
}
break;
case ParserActionTypes.Reduce:
{
var reduce = (ParserActionReduce)action;
var rule = reduce.Rule;
var lhs = Reduce(stack, rule);
// Push the LHS nonterminal on the stack.
//
stack.Push(lhs, stack.Peek().State.GetGoto(lhs.ElementType));
}
break;
default:
throw new InvalidOperationException(string.Format("Unrecognized action type {0}.", action.ActionType));
}
}
}
return(null);
}
