public AST expr()
{
var token = this.currentToken;
var tokenT = this.currentToken.getType();
//expr ::= [<unary_op>]<opnd>
if (tokenT == TokenType.NOT)
{
this.eatToken(TokenType.NOT);
return(this.checkStatus(new unaryOpNode(this.opnd(), token)));
}
//expr ::= <opnd> <op> <opnd>
AST node = this.opnd();
token = this.currentToken;
tokenT = this.currentToken.getType();
if (tokenT == TokenType.PLUS)
{
this.eatToken(TokenType.PLUS);
}
else if (tokenT == TokenType.MINUS)
{
this.eatToken(TokenType.MINUS);
}
else if (tokenT == TokenType.DIV)
{
this.eatToken(TokenType.DIV);
}
else if (tokenT == TokenType.MULT)
{
this.eatToken(TokenType.MULT);
}
else if (tokenT == TokenType.EQUALS)
{
this.eatToken(TokenType.EQUALS);
}
else if (tokenT == TokenType.LESSTHAN)
{
this.eatToken(TokenType.LESSTHAN);
}
else if (tokenT == TokenType.AND)
{
this.eatToken(TokenType.AND);
}
else
{
return(node);
}
node = new opNode(node, this.opnd(), token);
return(this.checkStatus(node));
}
private static Node MakeTree(string s, char op)
{
int pcounter = 0; // parenthesis counter
for (int i = s.Length - 1; i >= 0; i--) // 0 based indexing, start from right of the string
{
// keep count of total parentesis open and closed
if (')' == s[i]) // check if closing parenthesis
{
pcounter++;
}
else if ('(' == s[i]) // check for open parenthesis
{
pcounter--;
}
// no mismatching parenthesis set op to a valid op, do not want to set parenthesis to opnode
if (0 == pcounter && op == s[i])
{
opNode on = new opNode(s[i], MakeTree(s.Substring(0, i)), MakeTree(s.Substring(i + 1))); // make a new opnode
return(on);
}
}
if (pcounter != 0) // no matching parenthesis
{
if (pcounter < 0)
{
throw new Exception("Missing 1 or more closing parenthesis");
}
else
{
throw new Exception("missing 1 or more opening parenthesis");
}
}
return(null); // no node created
}
