public Runnable ProcessParseTree(ParseTree parseTree, IEnumerable<Error> parseErrors, bool isValidParseTree)
{
Runnable prog = new Runnable();
foreach (Error err in parseErrors)
{
prog.errors.Add(err);
}
// can't construct AST if parse tree is bad
if (!isValidParseTree)
return prog;
// first remove unnecessary symbols ; : .. ( ) := and epsilons
String[] pruneTokens = { "(", ")", ";", ":", "..", ":=", "var", "in", "for", "end", "do" };
Predicate<IParseNode> isUnnecessaryTerminal =
n => (n is ParseLeaf) ? (n as ParseLeaf).Token == null || pruneTokens.Contains((n as ParseLeaf).Token.Lexeme) : false;
parseTree.RemoveNodes(isUnnecessaryTerminal);
// remove any tree nodes with no children
Predicate<IParseNode> isEmptyNonterminal =
v => (v is ParseTree) ? (v as ParseTree).Children.Count == 0 : false;
parseTree.RemoveNodes(isEmptyNonterminal);
// refactor
// STMTS->STMTS_HEAD STMTS_TAIL to STMTS->(STMT)+
// DECL->"var" <IDENT> ":" <TYPE> ASSIGN to DECL->"var" <IDENT> ":" <TYPE> [":=" <EXPR>]
// EXPR->UNARY|OPND BINARY to EXPR-> unary_op OPND | OPND | OPND binary_op OPND
// OPND-><INT>|<STRING>|<IDENT>|<EXPR> to just <INT>|<STRING>|<IDENT>|<EXPR>
Nonterminal[] pruneVariables = new Nonterminal[] {
nonterminals["statements_head"], nonterminals["statements_tail"], nonterminals["unary_operation"],
nonterminals["binary_operation"], nonterminals["declaration_assignment"], nonterminals["operand"] };
Predicate<IParseNode> isUnnecessaryNonterminal =
n => (n is ParseTree) ? pruneVariables.Contains((n as ParseTree).Nonterminal) : false;
parseTree.RemoveNodes(isUnnecessaryNonterminal);
if (Program.debug) Console.WriteLine(parseTree);
// AST is formed at this point, so do semantic checks
// find declarations, produce errors if identifier declared multiple times
foreach (IParseNode node in parseTree.Nodes())
{
if (node is ParseTree)
{
ParseTree subtree = node as ParseTree;
if (subtree.Nonterminal == nonterminals["declaration"])
{
ParseLeaf idLeaf = (subtree.Children[0] as ParseLeaf);
ParseLeaf typeLeaf = (subtree.Children[1] as ParseLeaf);
Token idToken = idLeaf.Token;
Token typeToken = typeLeaf.Token;
string identifier = idToken.Lexeme;
ValueType type = Value.TypeFromString(typeToken.Lexeme);
Statement.DeclarationStmt declaration;
switch (subtree.Children.Count)
{
case 2: // simple declaration
declaration = new Statement.DeclarationStmt(identifier, type, idToken);
break;
case 3: // declaration with assignment
ParseLeaf valueLeaf = (subtree.Children[2] as ParseLeaf);
Expression expr = Expression.FromTreeNode(subtree.Children[2], terminals, nonterminals);
declaration = new Statement.DeclarationStmt(identifier, type, idToken, expr);
break;
default:
throw new Exception("BAD AST STRUCTURE");
}
if (prog.declarations.ContainsKey(identifier))
prog.errors.Add(new SemanticError(idToken, identifier + " multiply defined"));
else
prog.declarations[identifier] = declaration;
}
}
}
// check that variables are defined before use
foreach (IParseNode node in parseTree.Nodes())
{
if (node is ParseLeaf)
{
ParseLeaf leaf = node as ParseLeaf;
Token leafToken = leaf.Token;
if (leafToken.Type == tokenTypes["identifier"])
{
string identifier = leafToken.Lexeme;
Position idPosition = leafToken.TextPosition;
if (!prog.declarations.ContainsKey(identifier))
prog.errors.Add(new SemanticError(leafToken, identifier + " never defined"));
else if (idPosition.CompareTo(prog.declarations[identifier].Token.TextPosition) < 0)
prog.errors.Add(new SemanticError(leafToken, identifier + " not defined before use"));
}
}
}
// add statements to runnable
ParseTree statementListNode = parseTree.Children[0] as ParseTree;
foreach (IParseNode statementNode in statementListNode.Children)
prog.statements.Add(Statement.FromTreeNode(statementNode, terminals, nonterminals));
// check that for-loop control variables are not modified inside the for-loop
foreach (Statement stmt in prog.statements)
{
if (stmt is Statement.ForStmt)
{
Statement.ForStmt forStmt = stmt as Statement.ForStmt;
Stack<Statement> stmtStack = new Stack<Statement>();
foreach (Statement substmt in forStmt.Block)
stmtStack.Push(substmt);
while (stmtStack.Count != 0)
{
Statement s = stmtStack.Pop();
if (s is Statement.AssignStmt)
{
Statement.AssignStmt assignment = s as Statement.AssignStmt;
if (assignment.Identifier == forStmt.Identifier)
prog.errors.Add(new SemanticError(assignment.Token, forStmt.Identifier + " cannot be modified inside for-loop"));
}
else if (s is Statement.DeclarationStmt)
{
Statement.DeclarationStmt declaration = s as Statement.DeclarationStmt;
if (declaration.Identifier == forStmt.Identifier)
prog.errors.Add(new SemanticError(declaration.Token, forStmt.Identifier + " cannot be modified inside for-loop"));
}
else if (s is Statement.ForStmt)
{
Statement.ForStmt nestedFor = s as Statement.ForStmt;
if (nestedFor.Identifier == forStmt.Identifier)
prog.errors.Add(new SemanticError(nestedFor.Token, forStmt.Identifier + " cannot be modified inside for-loop"));
foreach (Statement substmt in nestedFor.Block)
stmtStack.Push(substmt);
}
}
}
}
// typecheck each statement
foreach (Statement stmt in prog.statements)
stmt.TypeCheck(prog);
return prog;
}
// 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);
}
