/// <summary>
/// Performs the given action on the given stack, branches, and current index based on the current item.
/// Returns whether the action was to accept.
/// </summary>
/// <param name="syntax"></param>
/// <param name="stateStack"></param>
/// <param name="currentBranches"></param>
/// <param name="action"></param>
/// <param name="currentIndex"></param>
/// <returns></returns>
protected bool PerformAction(bool syntax, Terminal <T> currentItem, Stack <KeyValuePair <int, GrammarElement <T> > > stateStack, List <SyntaxNode <T> > currentBranches, ParserAction <T> action, ref int currentIndex)
{
if (action is ShiftAction <T> )
{
Shift(stateStack, currentItem, action);
currentIndex++;
}
else if (action is ReduceAction <T> )
{
Reduce(syntax, stateStack, currentBranches, action, ref currentIndex);
currentIndex++;
}
else if (action is AcceptAction <T> )
{
return(true);
}
return(false);
}
/// <summary>
/// Reduces the given action, reflecting the changes on the given stack, branches, and index.
/// </summary>
/// <param name="syntax"></param>
/// <param name="stateStack"></param>
/// <param name="currentBranches"></param>
/// <param name="action"></param>
protected void Reduce(bool syntax, Stack <KeyValuePair <int, GrammarElement <T> > > stateStack, List <SyntaxNode <T> > currentBranches, ParserAction <T> action, ref int currentIndex)
{
if (action is ReduceAction <T> )
{
var r = (ReduceAction <T>)action;
var e = new List <GrammarElement <T> >();
//pop the number of elements in the RHS of the item
for (var c = 0; c < r.ReduceItem.ProductionElements.Length; c++)
{
e.Add(stateStack.Pop().Value);
}
e.Reverse();
//create a new branch with the value as the LHS of the reduction item.
var newBranch = new SyntaxNode <T>(r.ReduceItem.LeftHandSide);
//Determine whether to add each element to the new branch based on whether it should be kept.
foreach (GrammarElement <T> element in e)
{
if (element is NonTerminal <T> )
{
if (element.Keep || syntax)
{
//find the first branch that matches the reduce element
SyntaxNode <T> b = currentBranches.Last(a => a.Value.Equals(element));
newBranch.AddChild(b);
currentBranches.Remove(b);
}
else
{
//find the first branch that matches the reduce element
SyntaxNode <T> b = currentBranches.Last(a => a.Value.Equals(element));
//get the children of the branch since we don't want the current value
IEnumerable <SyntaxNode <T> > branches = b.GetChildren();
//add the children
newBranch.AddChildren(branches);
currentBranches.Remove(b);
}
}
else
{
//if we should keep the terminal object, then add it to the new branch
if (element == null ||
element.Keep ||
syntax)
{
newBranch.AddChild(new SyntaxNode <T>(element));
}
}
}
currentBranches.Add(newBranch);
//push the LHS non-terminal and the next state
stateStack.Push(new KeyValuePair <int, GrammarElement <T> >(ParseTable.GotoTable[stateStack.Peek().Key, r.ReduceItem.LeftHandSide].Value, r.ReduceItem.LeftHandSide));
currentIndex--;
}
}
/// <summary>
/// Shifts the given action based on the given item, reflecting the given changes on the given stack.
/// </summary>
/// <param name="stateStack"></param>
/// <param name="item"></param>
/// <param name="action"></param>
protected static void Shift(Stack <KeyValuePair <int, GrammarElement <T> > > stateStack, Terminal <T> item, ParserAction <T> action)
{
//push the state and item
stateStack.Push(new KeyValuePair <int, GrammarElement <T> >(((ShiftAction <T>)action).NextState, item));
}
