public object Visit(Expr.Prefix prefix)
{
object right = Evaluate(prefix.rhs);
switch (prefix.opp.type)
{
case TokenType.Bang:
return(!IsTrue(right));
case TokenType.Minus:
ValidateNumberOperand(prefix.opp, right);
return(-(double)right);
case TokenType.MinusMinus:
ValidateNumberOperand(prefix.opp, right);
return((double)right - 1);
case TokenType.PlusPlus:
ValidateNumberOperand(prefix.opp, right);
return((double)right + 1);
}
// Unreachable
return(null);
}
public object Visit(Expr.Prefix _prefix)
{
return(null);
}
string Expr.IVisitor <string> .Visit(Expr.Prefix prefix)
{
return(Parenthesize(prefix.opp.lexeme, prefix.rhs));
}