protected void OnActionSelected(Token input, ActionRecord action)
{
Data.Grammar.OnActionSelected(this, _currentToken, action);
if (ActionSelected != null)
{
ParserActionEventArgs args = new ParserActionEventArgs(this.CurrentState, input, action);
ActionSelected(this, args);
}
}
}//methods
private bool CheckConflictResolutionByPrecedence(ActionRecord action)
{
SymbolTerminal opTerm = SymbolTerminal.GetSymbol(action.Key);
if (opTerm != null && opTerm.IsSet(TermOptions.IsOperator))
{
action.ActionType = ParserActionType.Operator;
action.ConflictResolved = true;
return(true);
}
return(false);
}
//TODO: need to rewrite, looks ugly
private bool Recover()
{
//for recovery the current token must be error token, we rely on it
if (!_currentToken.IsError())
{
_currentToken = _context.CreateErrorToken(_currentToken.Location, _currentToken.Text);
}
//Check the current state and states in stack for error shift action - this would be recovery state.
ActionRecord action = GetCurrentAction();
if (action == null || action.ActionType == ParserActionType.Reduce)
{
while (Stack.Count > 0)
{
_currentState = Stack.Top.State;
Stack.Pop(1);
action = GetCurrentAction();
if (action != null && action.ActionType != ParserActionType.Reduce)
{
break; //we found shift action for error token
}
}//while
}//if
if (action == null || action.ActionType == ParserActionType.Reduce)
{
return(false); //could not find shift action, cannot recover
}
//We found recovery state, and action contains ActionRecord for "error shift". Lets shift it.
ExecuteShiftAction(action);//push the error token
// Now shift all tokens from input that can be shifted.
// These are the ones that are found in error production after the error. We ignore all other tokens
// We stop when we find a state with reduce-only action.
while (_currentToken.Terminal != Grammar.Eof)
{
//with current token, see if we can shift it.
action = GetCurrentAction();
if (action == null)
{
NextToken(); //skip this token and continue reading input
continue;
}
if (action.ActionType == ParserActionType.Reduce || action.ActionType == ParserActionType.Operator)
{
//we can reduce - let's reduce and return success - we recovered.
ExecuteReduceAction(action);
return(true);
}
//it is shift action, let's shift
ExecuteShiftAction(action);
}//while
return(false); //
}
} //method
//Checks Reduce productions of an action for a ReduceThis hint. If found, the production is moved to the beginning of the list.
private bool CheckReduceHint(ActionRecord action)
{
foreach (Production prod in action.ReduceProductions)
{
GrammarHint reduceHint = GetHint(prod, prod.RValues.Count, HintType.ReduceThis);
if (reduceHint != null)
{
action.ReduceProductions.Remove(prod);
action.ReduceProductions.Insert(0, prod);
action.ActionType = ParserActionType.Reduce;
action.ConflictResolved = true;
return(true);
} //if
} //foreach prod
return(false);
} //method
//Checks shift items for PreferShift grammar hint. Hints are associated with a particular position
// inside production, which is in fact an LR0 item. The LR0 item is available thru shiftItem.Core property.
// If PreferShift hint found, moves the hint-owning shiftItem to the beginning of the list and returns true.
private bool CheckShiftHint(ActionRecord action)
{
foreach (LRItem shiftItem in action.ShiftItems)
{
GrammarHint shiftHint = GetHint(shiftItem.Core.Production, shiftItem.Core.Position, HintType.PreferShift);
if (shiftHint != null)
{
action.ActionType = ParserActionType.Shift;
action.ShiftItems.Remove(shiftItem);
action.ShiftItems.Insert(0, shiftItem);
action.ConflictResolved = true;
return(true);
} //if
} //foreach shiftItem
return(false);
} //method
private void CreateParserStates()
{
Data.States.Clear();
_stateHash = new ParserStateTable();
CreateInitialAndFinalStates();
string augmRootKey = Data.AugmentedRoot.Key;
// Iterate through states (while new ones are created) and create shift transitions and new states
for (int index = 0; index < Data.States.Count; index++)
{
ParserState state = Data.States[index];
AddClosureItems(state);
//Get keys of all possible shifts
ShiftTable shiftTable = GetStateShifts(state);
//Each key in shifts dict is an input element
// Value is LR0ItemList of shifted LR0Items for this input element.
foreach (string input in shiftTable.Keys)
{
LR0ItemList shiftedCoreItems = shiftTable[input];
ParserState newState = FindOrCreateState(shiftedCoreItems);
ActionRecord newAction = new ActionRecord(input, ParserActionType.Shift, newState, null);
state.Actions[input] = newAction;
//link original LRItems in original state to derived LRItems in newState
foreach (LR0Item coreItem in shiftedCoreItems)
{
LRItem fromItem = FindItem(state, coreItem.Production, coreItem.Position - 1);
LRItem toItem = FindItem(newState, coreItem.Production, coreItem.Position);
if (!fromItem.PropagateTargets.Contains(toItem))
{
fromItem.PropagateTargets.Add(toItem);
}
//copy hints from core items into the newAction
newAction.ShiftItems.Add(fromItem);
} //foreach coreItem
} //foreach input
} //for index
Data.FinalState = Data.InitialState.Actions[augmRootKey].NewState;
} //method
private ActionRecord GetCurrentAction()
{
ActionRecord action = null;
if (_currentToken.MatchByValue)
{
string key = CurrentToken.Text;
if (!_caseSensitive)
{
key = key.ToLower();
}
if (_currentState.Actions.TryGetValue(key, out action))
{
return(action);
}
}
if (_currentToken.MatchByType && _currentState.Actions.TryGetValue(_currentToken.Terminal.Key, out action))
{
return(action);
}
return(null); //action not found
}
public ParserActionEventArgs(ParserState state, Token input, ActionRecord action)
{
State = state;
Input = input;
Action = action;
}
}//method
private AstNode CreateNode(ActionRecord reduceAction, SourceSpan sourceSpan, AstNodeList childNodes)
{
NonTerminal nt = reduceAction.NonTerminal;
AstNode result;
NodeArgs nodeArgs = new NodeArgs(_context, nt, sourceSpan, childNodes);
if (nt.NodeCreator != null)
{
result = nt.NodeCreator(nodeArgs);
if (result != null)
{
return(result);
}
}
Type defaultNodeType = _context.Compiler.Grammar.DefaultNodeType;
Type ntNodeType = nt.NodeType ?? defaultNodeType ?? typeof(AstNode);
// Check if NonTerminal is a list
// List nodes are produced by .Plus() or .Star() methods of BnfElement
// In this case, we have a left-recursive list formation production:
// ntList -> ntList + delim? + ntElem
// We check if we have already created the list node for ntList (in the first child);
// if yes, we use this child as a result directly, without creating new list node.
// The other incoming child - the last one - is a new list member;
// we simply add it to child list of the result ntList node. Optional "delim" node is simply thrown away.
bool isList = nt.IsSet(TermOptions.IsList);
if (isList && childNodes.Count > 1 && childNodes[0].Term == nt)
{
result = childNodes[0];
AstNode newChild = childNodes[childNodes.Count - 1];
newChild.Parent = result;
result.ChildNodes.Add(newChild);
return(result);
}
//Check for StarList produced by MakeStarRule; in this case the production is: ntList -> Empty | Elem+
// where Elem+ is non-empty list of elements. The child list we are actually interested in is one-level lower
if (nt.IsSet(TermOptions.IsStarList) && childNodes.Count == 1)
{
childNodes = childNodes[0].ChildNodes;
}
// Check for "node-bubbling" case. For identity productions like
// A -> B
// the child node B is usually a subclass of node A,
// so child node B can be used directly in place of the A. So we simply return child node as a result.
// TODO: probably need a grammar option to enable/disable this behavior explicitly
bool canBubble = (Data.Grammar.FlagIsSet(LanguageFlags.BubbleNodes)) &&
!isList && !nt.IsSet(TermOptions.IsPunctuation) && childNodes.Count == 1 && (childNodes[0].Term is NonTerminal);
if (canBubble)
{
NonTerminal childNT = childNodes[0].Term as NonTerminal;
Type childNodeType = childNT.NodeType ?? defaultNodeType ?? typeof(AstNode);
if (childNodeType == ntNodeType || childNodeType.IsSubclassOf(ntNodeType))
{
return(childNodes[0]);
}
}
// Try using Grammar's CreateNode method
result = Data.Grammar.CreateNode(_context, reduceAction, sourceSpan, childNodes);
if (result != null)
{
return(result);
}
//Finally create node directly. For perf reasons we try using "new" for AstNode type (faster), and
// activator for all custom types (slower)
if (ntNodeType == typeof(AstNode))
{
return(new AstNode(nodeArgs));
}
// if (ntNodeType.GetConstructor(new Type[] {typeof(AstNodeList)}) != null)
// return (AstNode)Activator.CreateInstance(ntNodeType, childNodes);
if (ntNodeType.GetConstructor(new Type[] { typeof(NodeArgs) }) != null)
{
return((AstNode)Activator.CreateInstance(ntNodeType, nodeArgs));
}
//The following should never happen - we check that constructor exists when we validate grammar.
string msg = string.Format(
@"AST Node class {0} does not have a constructor for automatic node creation.
Provide a constructor with a single NodeArgs parameter, or use NodeCreator delegate property in NonTerminal.", ntNodeType);
throw new GrammarErrorException(msg);
}
private void ExecuteReduceAction(ActionRecord action)
{
ParserState oldState = _currentState;
int popCnt = action.PopCount;
//Get new node's child nodes - these are nodes being popped from the stack
AstNodeList childNodes = new AstNodeList();
for (int i = 0; i < action.PopCount; i++)
{
AstNode child = Stack[Stack.Count - popCnt + i].Node;
if (child.Term.IsSet(TermOptions.IsPunctuation))
{
continue;
}
//Transient nodes - don't add them but add their childrent directly to grandparent
if (child.Term.IsSet(TermOptions.IsTransient))
{
foreach (AstNode grandChild in child.ChildNodes)
{
childNodes.Add(grandChild);
}
continue;
}
//Add normal child
childNodes.Add(child);
}
//recover state, location and pop the stack
SourceSpan newNodeSpan;
if (popCnt == 0)
{
newNodeSpan = new SourceSpan(_currentToken.Location, 0);
}
else
{
SourceLocation firstPopLoc = Stack[Stack.Count - popCnt].Node.Location;
int lastPopEndPos = Stack[Stack.Count - 1].Node.Span.EndPos;
newNodeSpan = new SourceSpan(firstPopLoc, lastPopEndPos - firstPopLoc.Position);
_currentState = Stack[Stack.Count - popCnt].State;
Stack.Pop(popCnt);
}
//Create new node
AstNode node = CreateNode(action, newNodeSpan, childNodes);
action.NonTerminal.OnNodeCreated(node);
// Push node/current state into the stack
Stack.Push(node, _currentState);
//switch to new state
ActionRecord gotoAction;
if (_currentState.Actions.TryGetValue(action.NonTerminal.Key, out gotoAction))
{
_currentState = gotoAction.NewState;
}
else
{
//should never happen
throw new CompilerException(string.Format("Cannot find transition for input {0}; state: {1}, popped state: {2}",
action.NonTerminal, oldState, _currentState));
}
}//method
private void ExecuteShiftAction(ActionRecord action)
{
Stack.Push(_currentToken, _currentState);
_currentState = action.NewState;
NextToken();
}
}//method
public AstNode Parse(CompilerContext context, IEnumerable <Token> tokenStream)
{
_context = context;
_caseSensitive = _context.Compiler.Grammar.CaseSensitive;
Reset();
_input = tokenStream.GetEnumerator();
NextToken();
while (true)
{
if (_currentState == Data.FinalState)
{
AstNode result = Stack[0].Node;
//Check transient status
if (result.Term.IsSet(TermOptions.IsTransient) && result.ChildNodes.Count == 1)
{
result = result.ChildNodes[0];
}
Stack.Reset();
return(result);
}
//check for scammer error
if (_currentToken.IsError())
{
if (!Recover())
{
return(null);
}
continue;
}
//Get action
ActionRecord action = GetCurrentAction();
if (action == null)
{
ReportParseError();
if (!Recover())
{
return(null); //did not recover
}
continue;
}//action==null
if (action.HasConflict())
{
action = (ActionRecord)Data.Grammar.OnActionConflict(this, _currentToken, action);
}
this.OnActionSelected(_currentToken, action);
switch (action.ActionType)
{
case ParserActionType.Operator:
if (GetActionTypeForOperation(_currentToken) == ParserActionType.Shift)
{
goto case ParserActionType.Shift;
}
else
{
goto case ParserActionType.Reduce;
}
case ParserActionType.Shift:
ExecuteShiftAction(action);
break;
case ParserActionType.Reduce:
ExecuteReduceAction(action);
break;
} //switch
} //while
} //Parse
