/// <summary>
/// Productions MUST BE:
/// - left factored
/// - without left recursions
/// </summary>
/// <param name="productions">Processed productions</param>
public void FillByProcessedProductions(IEnumerable <Production> productions, Nonterminal axiom)
{
// A -> alpha
foreach (var production in productions)
{
var useProductionAction = AutomateAction.FromProduction(production);
// FIRST(alpha)
var first = Helper.First(productions, production.RightPart);
foreach (var terminal in first)
{
this[production.LeftPart, terminal] = useProductionAction;
}
if (first.Contains(GeneralizedTerminal.Epsilon))
{
// FOLLOW(A)
var follow = Helper.Follow(productions, production.LeftPart, axiom);
foreach (var terminal in follow)
{
this[production.LeftPart, terminal] = useProductionAction;
}
}
}
}
private StepResults Step(out Error error)
{
if (_stack.Count == 0)
#region When stack is empty
{
if (_tokenStream.Current.Type == TokenType.EndOfText)
#region ACCEPT
{
error = null;
return(StepResults.AcceptInput);
}
#endregion
else
#region REJECT: EOF EXPECTED
{
error = new Error(_tokenStream.Current, ErrorKind.Syntax, "End of input expected");
return(StepResults.RejectInput);
}
#endregion
}
#endregion
else
#region When stack is not empty
{
Symbol magazineSymbol = _stack.Peek();
ConcreteTerminal inputTerminal = new ConcreteTerminal(_tokenStream.Current);
if (magazineSymbol is Nonterminal)
{
var magazineNonterminal = (Nonterminal)magazineSymbol;
AutomateAction action = _controlTable[magazineNonterminal, inputTerminal];
if (action == null && CanBeEpsilon(magazineNonterminal))
{
_stack.Pop();
error = null;
return(StepResults.InProgress);
}
if (action == null) // common error handling
{
error = new Error(_tokenStream.Current, ErrorKind.Syntax, GenerateErrorMessage(magazineNonterminal, inputTerminal));
return(StepResults.RejectInput);
}
switch (action.Kind)
{
case AutomateActionKind.UseProduction:
_stack.Pop(); // delete disclosing nonterminal
Production production = action.GetProduction();
if (!production.RightPart.IsEpsilonChain)
{
production.RightPart.ReverseForEach(s => _stack.Push(s)); // and push right parts of productions
}
ConstructSyntaxTree(production);
break;
case AutomateActionKind.HandleError: // custom error handling
break;
default: break;
}
error = null;
return(StepResults.InProgress);
}
else // magazineSymbol is Terminal
{
var magazineTerminal = (Terminal)magazineSymbol;
if (magazineTerminal.IsAppropriateTerminal(inputTerminal))
{
_stack.Pop();
_tokenStream.MoveNext();
SubstituteTreeTerminalByActualValue(magazineTerminal, inputTerminal);
error = null;
return(StepResults.InProgress);
}
else
{
error = new Error(_tokenStream.Current, ErrorKind.Syntax, GenerateErrorMessage(magazineTerminal, inputTerminal));
return(StepResults.RejectInput);
}
}
}
#endregion
}
