private void ValidateNoUndeclaredNonterminal()
{
foreach (var item in Productions)
{
foreach (var nt in item.Body.Where(x => x is NonterminalSymbol).Cast <NonterminalSymbol>())
{
if (!Productions.Any(x => x.Head == nt))
{
throw new GrammarException(new Location(), $"símbolo {nt} não declarado");
}
}
}
}
/// <summary>
/// Gets a collection of Terminal elements that can appear after the element that is after the dot of the item.
/// </summary>
/// <example>
/// With Grammar:
/// S -> E
/// E -> T
/// E -> (E)
/// T -> n
/// T -> + T
/// T -> T + n
/// Follow(S -> •E) : {$}
/// Follow(T -> •+ T) : {'+', 'n'}
/// Follow(T -> •n, ')') : {')'}
/// </example>
/// <param name="nonTerminal"></param>
/// <returns></returns>
private IEnumerable <Terminal <T> > Follow(LRItem <T> item, IEnumerable <LRItem <T> > totalItems)
{
//Follow(item) is First(b) where item is:
//A -> a•Eb
GrammarElement <T> element = item.GetNextElement(1);
if (element != null)
{
if (element is NonTerminal <T> )
{
var firstSet = new List <Terminal <T> >();
//if the element has a production with no derived elements and the element is at the end of the current item's production, then
//add the lookahead of the given item.
//if there is any production of the current element that has no derived elements
if (Productions.Any(a => a.NonTerminal.Equals(element) && a.DerivedElements.Count == 0))
{
//if the current element is the end of the current item's production
if (item.GetNextElement(2) == null)
{
firstSet.Add(item.LookaheadElement ?? EndOfInputElement);
}
}
//select the lookahead element or end of input element for each item in the previous set
//List<Terminal<T>> firstSet = new List<Terminal<T>>(items.Select(a => a.LookaheadElement == null ? EndOfInputElement : a.LookaheadElement));
//add the rest of the first set.
firstSet.AddRange(First(element));
return(firstSet);
}
return(First(element));
}
if (item.LookaheadElement == null)
{
return new[] { EndOfInputElement }
}
;
return(new[] { item.LookaheadElement });
}