public (Item?, ParseAction) FindTransitionOfItemOn(Item item, Symbol symbol)
{
var(target, action) = FindTransitionOfItemOnUnchecked(item, symbol);
return(TransitionIsValidForItem(action, item, symbol)
? (target, action)
: (null, ParseAction.MakeDiscard()));
}
private (Item?, ParseAction) FindTransitionOfItemOnUnchecked(Item item, Symbol symbol)
{
var productionLen = item.Production.Ingredients.Length;
if (item.DotPos < productionLen && symbol == item.Production.Ingredients[item.DotPos])
{
return(item.ShiftedByOne(), ParseAction.MakeShift());
}
if (item.DotPos >= productionLen && symbol == item.Follow)
{
if (symbol == Symbol.EndOfInput && item.Production.Product == Symbol.ExtendedStartSymbol)
{
return(null, ParseAction.MakeAccept());
}
return(null, ParseAction.MakeReduce(item.Production));
}
return(null, ParseAction.MakeDiscard());
}