public override void Apply(LanguageData language, LRItem owner)
{
var state = owner.State;
var allConflicts = state.BuilderData.Conflicts;
if (allConflicts.Count == 0)
{
return;
}
//Find all conflicts that can be resolved by operator precedence
// SL does not support Find extension, so we do it with explicit loop
var operConflicts = new List <Terminal>();
foreach (var c in allConflicts)
{
if (c.Flags.IsSet(TermFlags.IsOperator))
{
operConflicts.Add(c);
}
}
foreach (var conflict in operConflicts)
{
var newState = state.BuilderData.GetNextState(conflict);
var reduceItems = state.BuilderData.ReduceItems.SelectByLookahead(conflict).ToList();
if (newState == null || reduceItems.Count != 1)
{
continue; // this cannot be fixed by precedence
}
state.Actions[conflict] = new PrecedenceBasedParserAction(conflict, newState, reduceItems[0].Core.Production);
allConflicts.Remove(conflict);
} //foreach conflict
}
public void AddItem(LR0Item core)
{
//Check if a core had been already added. If yes, simply return
if (!_allCores.Add(core))
{
return;
}
//Create new item, add it to AllItems, InitialItems, ReduceItems or ShiftItems
var item = new LRItem(_state, core);
AllItems.Add(item);
if (item.Core.IsFinal)
{
ReduceItems.Add(item);
}
else
{
ShiftItems.Add(item);
}
if (item.Core.IsInitial)
{
InitialItems.Add(item);
}
if (core.IsFinal)
{
return;
}
//Add current term to ShiftTerms
if (!ShiftTerms.Add(core.Current))
{
return;
}
if (core.Current is Terminal)
{
ShiftTerminals.Add(core.Current as Terminal);
}
//If current term (core.Current) is a new non-terminal, expand it
var currNt = core.Current as NonTerminal;
if (currNt == null)
{
return;
}
foreach (var prod in currNt.Productions)
{
AddItem(prod.LR0Items[0]);
}
}
public override void Apply(LanguageData language, LRItem owner)
{
var state = owner.State;
var conflicts = state.BuilderData.Conflicts;
if (conflicts.Count == 0)
{
return;
}
switch (ActionType)
{
case PreferredActionType.Shift:
var currTerm = owner.Core.Current as Terminal;
if (currTerm == null || !conflicts.Contains(currTerm))
{
return; //nothing to do
}
//Current term for shift item (hint owner) is a conflict - resolve it with shift action
var newState = owner.ShiftedItem.State;
var shiftAction = new ShiftParserAction(owner);
state.Actions[currTerm] = shiftAction;
conflicts.Remove(currTerm);
return;
case PreferredActionType.Reduce:
if (!owner.Core.IsFinal)
{
return; //we take care of reduce items only here
}
//we have a reduce item with "Reduce" hint. Check if any of lookaheads are in conflict
ReduceParserAction reduceAction = null;
foreach (var lkhead in owner.Lookaheads)
{
if (conflicts.Contains(lkhead))
{
if (reduceAction == null)
{
reduceAction = new ReduceParserAction(owner.Core.Production);
}
state.Actions[lkhead] = reduceAction;
conflicts.Remove(lkhead);
}
}
return;
} //switch
} //method
/// <summary> Gives a chance to a custom code in hint to interfere in parser automaton construction.</summary>
/// <param name="language">The LanguageData instance.</param>
/// <param name="owner">The LRItem that "owns" the hint. </param>
/// <remarks>
/// The most common purpose of this method (it's overrides) is to resolve the conflicts
/// by adding specific actions into State.Actions dictionary.
/// The owner parameter represents the position in the grammar expression where the hint
/// is found. The parser state is available through owner.State property.
/// </remarks>
public virtual void Apply(LanguageData language, LRItem owner)
{
// owner.State -- the parser state
// owner.State.BuilderData.Conflicts -- as set of conflict terminals
// owner.State.Actions -- a dictionary of actions in the current state.
}