private AST ParseAssignment(AST node)
{
while (_lexer.CurrentToken.Type == TokenType.Assign)
{
if (node.GetType() == typeof(FnCallAST))
{
throw new Exception($"Syntax error - function {node.Value} cannot be assigned to");
}
_lexer.AcceptToken(TokenType.Assign);
var expr = ParseExpr();
node = new BinaryOpAST(node, "=", expr);
}
return(node);
}
private AST ParseTerm(List <string> ns)
{
// term ::= factor | (*\/|%) factor
var factor = ParseFactor(ns);
var token = _lexer.CurrentToken;
while (token.Type == TokenType.Mul || token.Type == TokenType.Div || token.Type == TokenType.Mod)
{
_lexer.AcceptToken(token.Type);
var otherFactor = ParseFactor(ns);
factor = new BinaryOpAST(factor, token.Value, otherFactor);
token = _lexer.CurrentToken;
}
return(factor);
}
private AST ParseExpr(List <string> ns = null)
{
// expr ::= term | (+\-) factor
var term = ParseTerm(ns);
var token = _lexer.CurrentToken;
while (token.Type == TokenType.Add || token.Type == TokenType.Sub)
{
_lexer.AcceptToken(token.Type);
var otherTerm = ParseTerm(ns);
term = new BinaryOpAST(term, token.Value, otherTerm);
token = _lexer.CurrentToken;
}
return(term);
}
