public void Visit(AssignmentStmt node)
{
try {
string name = node.Children [0].Name;
if (!SymbolTable.ContainsKey (name)) {
throw new SemanticError ("Variable " + name +
" needs to be declared before use", node.Children [0].Row,
node.Children [0].Column);
}
// check if the assigned expression is of the same type as the variable in symbol table
VisitChildren (node.Children [1]);
string type = TypeStack.Pop ();
if (type != SymbolTable [name].Type) {
throw new SemanticError ("Variable " + name + " of type " + SymbolTable [name].Type +
" can not be assigned a value of type " + type, node.Children [0].Row, node.Children [0].Column);
}
} catch (SemanticError error) {
Errors.Add (error);
TypeStack.Clear ();
}
}
public void Visit(AssignmentStmt node)
{
string name = node.Children [0].Name;
// visit the children, the value should be on top of the stack after that
VisitChildren (node.Children [1]);
StackValue stackValue = ValueStack.Pop ();
// update the value in symbol table
SymbolTable [name].Value = stackValue.Value;
}
private Statement Stmt()
{
switch ((Token.Types)currentToken.Type) {
case Token.Types.Var:
VarDeclStmt varDeclStmt = new VarDeclStmt ("VarDecl", currentToken.Row, currentToken.Column);
Match (Token.Types.Var);
varDeclStmt.AddChild (IdentifierNameStmt ());
Match (Token.Types.Colon);
varDeclStmt.AddChild (Type ());
if ((Token.Types)currentToken.Type == Token.Types.Assign) {
Match (Token.Types.Assign);
varDeclStmt.AddChild (Expr ());
return varDeclStmt;
} else if ((Token.Types)currentToken.Type == Token.Types.Semicolon) {
return varDeclStmt;
}
throw new SyntaxError ("Expected Assign, got: " + currentToken.Type, currentToken.Row, currentToken.Column);
case Token.Types.Identifier:
AssignmentStmt assignmentStmt = new AssignmentStmt ("AssignmentStmt", currentToken.Row, currentToken.Column);
assignmentStmt.AddChild (IdentifierNameStmt ());
Match (Token.Types.Assign);
assignmentStmt.AddChild (Expr ());
return assignmentStmt;
case Token.Types.For:
ForStmt forStmt = new ForStmt ("ForStmt", currentToken.Row, currentToken.Column);
Match (Token.Types.For);
forStmt.AddChild (IdentifierNameStmt ());
Match (Token.Types.In);
forStmt.AddChild (Expr ());
Match (Token.Types.Range);
forStmt.AddChild (Expr ());
Match (Token.Types.Do);
forStmt.AddChild (Stmts ());
Match (Token.Types.End);
Match (Token.Types.For);
return forStmt;
case Token.Types.Read:
ReadStmt readStmt = new ReadStmt ("ReadStmt", currentToken.Row, currentToken.Column);
Match (Token.Types.Read);
readStmt.AddChild (IdentifierNameStmt ());
return readStmt;
case Token.Types.Print:
PrintStmt printStmt = new PrintStmt ("PrintStmt", currentToken.Row, currentToken.Column);
Match (Token.Types.Print);
printStmt.AddChild (Expr ());
return printStmt;
case Token.Types.Assert:
AssertStmt assertStmt = new AssertStmt ("AssertStmt", currentToken.Row, currentToken.Column);
Match (Token.Types.Assert);
Match (Token.Types.LeftParenthesis);
assertStmt.AddChild (Expr ());
Match (Token.Types.RightParenthesis);
return assertStmt;
default:
throw new SyntaxError ("invalid start symbol for statement " + currentToken.Lexeme,
currentToken.Row, currentToken.Column);
}
}