// Creates an indentifier or value expression from an abstract syntax tree leaf
private static Expression ExprFromLeaf(ParseLeaf leaf)
{
if (leaf == null) throw new Exception("MALFORMED AST");
if (leaf.Token.Type.Name == "identifier")
return new IdentifierExpr(leaf.Token.Lexeme, leaf.Token);
else
return new ValueExpr(new Value(leaf.Token.Type.Name, leaf.Token.Lexeme), leaf.Token);
}
// Parse the given stream of tokens
public ParseTree Parse(IEnumerable<Token> tokenSource)
{
isValidParseTree = true;
errors = new List<Error>();
Stack<ISymbol> symbolStack = new Stack<ISymbol>();
symbolStack.Push(Terminal.EOF);
symbolStack.Push(start);
ParseTree parseTree = new ParseTree(start);
Stack<IParseNode> treeStack = new Stack<IParseNode>();
treeStack.Push(new ParseLeaf(Terminal.EOF));
treeStack.Push(parseTree);
IEnumerator<Token> tokenStream = tokenSource.GetEnumerator();
tokenStream.MoveNext();
while (symbolStack.Count > 0)
{
if (Program.debug)
{
Console.WriteLine("=========================================================");
Console.WriteLine(" PARSE: Stack " + SymbolsToString(symbolStack));
Console.WriteLine(" PARSE: expecting " + symbolStack.Peek());
Console.WriteLine(" PARSE: token " + tokenStream.Current);
}
// ignore error tokens
if (tokenStream.Current.Type == TokenType.ERROR)
{
if (Program.debug)
Console.WriteLine(" PARSE: skipping error token");
errors.Add(new LexicalError(tokenStream.Current));
tokenStream.MoveNext();
continue;
}
if (symbolStack.Peek() is Terminal)
{
Terminal term = symbolStack.Peek() as Terminal;
ParseLeaf leaf = treeStack.Peek() as ParseLeaf;
if (term == Terminal.EPSILON)
{
// epsilon production was used, exclude from parse tree
if (Program.debug)
Console.WriteLine(" PARSE: ignore epsilon");
symbolStack.Pop();
treeStack.Pop();
}
else if (term.Matches(tokenStream.Current))
{
// current token matches the top of the parse stack, add it to parse tree
if (Program.debug)
Console.WriteLine(" PARSE: Terminal match");
leaf.Token = tokenStream.Current;
tokenStream.MoveNext();
symbolStack.Pop();
treeStack.Pop();
}
else
{
// current token does no match, recover from error
if (Program.debug)
Console.WriteLine(" PARSE: Error, Terminal mismatch");
errors.Add(new SyntaxError(tokenStream.Current));
Synchronize(symbolStack, treeStack, tokenStream);
}
}
else // top of stack is a nonterminal
{
Nonterminal var = symbolStack.Pop() as Nonterminal;
IParseNode popped = treeStack.Pop();
ParseTree subtree = popped as ParseTree;
ISymbol[] production = table.Get(var, tokenStream.Current);
if (production == null)
{
// cannot derive the current token from the nonterminal at the top of the stack
if (Program.debug)
Console.WriteLine(" PARSE: Error, No such production");
symbolStack.Push(var);
treeStack.Push(popped);
errors.Add(new SyntaxError(tokenStream.Current));
Synchronize(symbolStack, treeStack, tokenStream);
}
else
{
// use the production specified by the parse table, add node to parse tree
if (Program.debug)
Console.WriteLine(" PARSE: Using production " + SymbolsToString(production));
for (int i = production.Length - 1; i >= 0; i--)
{
IParseNode treeChild;
if (production[i] is Terminal)
treeChild = new ParseLeaf(production[i] as Terminal);
else
treeChild = new ParseTree(production[i] as Nonterminal);
subtree.Children.Insert(0, treeChild);
treeStack.Push(treeChild);
symbolStack.Push(production[i]);
}
}
}
}
if (Program.debug)
Console.WriteLine(parseTree);
return parseTree;
}
// Parse the given stream of tokens
public ParseTree Parse(IEnumerable <Token> tokenSource)
{
isValidParseTree = true;
errors = new List <Error>();
Stack <ISymbol> symbolStack = new Stack <ISymbol>();
symbolStack.Push(Terminal.EOF);
symbolStack.Push(start);
ParseTree parseTree = new ParseTree(start);
Stack <IParseNode> treeStack = new Stack <IParseNode>();
treeStack.Push(new ParseLeaf(Terminal.EOF));
treeStack.Push(parseTree);
IEnumerator <Token> tokenStream = tokenSource.GetEnumerator();
tokenStream.MoveNext();
while (symbolStack.Count > 0)
{
if (Program.debug)
{
Console.WriteLine("=========================================================");
Console.WriteLine(" PARSE: Stack " + SymbolsToString(symbolStack));
Console.WriteLine(" PARSE: expecting " + symbolStack.Peek());
Console.WriteLine(" PARSE: token " + tokenStream.Current);
}
// ignore error tokens
if (tokenStream.Current.Type == TokenType.ERROR)
{
if (Program.debug)
{
Console.WriteLine(" PARSE: skipping error token");
}
errors.Add(new LexicalError(tokenStream.Current));
tokenStream.MoveNext();
continue;
}
if (symbolStack.Peek() is Terminal)
{
Terminal term = symbolStack.Peek() as Terminal;
ParseLeaf leaf = treeStack.Peek() as ParseLeaf;
if (term == Terminal.EPSILON)
{
// epsilon production was used, exclude from parse tree
if (Program.debug)
{
Console.WriteLine(" PARSE: ignore epsilon");
}
symbolStack.Pop();
treeStack.Pop();
}
else if (term.Matches(tokenStream.Current))
{
// current token matches the top of the parse stack, add it to parse tree
if (Program.debug)
{
Console.WriteLine(" PARSE: Terminal match");
}
leaf.Token = tokenStream.Current;
tokenStream.MoveNext();
symbolStack.Pop();
treeStack.Pop();
}
else
{
// current token does no match, recover from error
if (Program.debug)
{
Console.WriteLine(" PARSE: Error, Terminal mismatch");
}
errors.Add(new SyntaxError(tokenStream.Current));
Synchronize(symbolStack, treeStack, tokenStream);
}
}
else // top of stack is a nonterminal
{
Nonterminal var = symbolStack.Pop() as Nonterminal;
IParseNode popped = treeStack.Pop();
ParseTree subtree = popped as ParseTree;
ISymbol[] production = table.Get(var, tokenStream.Current);
if (production == null)
{
// cannot derive the current token from the nonterminal at the top of the stack
if (Program.debug)
{
Console.WriteLine(" PARSE: Error, No such production");
}
symbolStack.Push(var);
treeStack.Push(popped);
errors.Add(new SyntaxError(tokenStream.Current));
Synchronize(symbolStack, treeStack, tokenStream);
}
else
{
// use the production specified by the parse table, add node to parse tree
if (Program.debug)
{
Console.WriteLine(" PARSE: Using production " + SymbolsToString(production));
}
for (int i = production.Length - 1; i >= 0; i--)
{
IParseNode treeChild;
if (production[i] is Terminal)
{
treeChild = new ParseLeaf(production[i] as Terminal);
}
else
{
treeChild = new ParseTree(production[i] as Nonterminal);
}
subtree.Children.Insert(0, treeChild);
treeStack.Push(treeChild);
symbolStack.Push(production[i]);
}
}
}
}
if (Program.debug)
{
Console.WriteLine(parseTree);
}
return(parseTree);
}
