Value eval(Value arg, Table env) {
if (arg.tag == ConsCell) {
Value operator = car(arg);
Value operands = cdr(arg); // <- debugger stopped here
If I print the argument arg with p arg, I get:
(lldb) p arg
(Value) $0 = {
data = {
number = 1068272
list = 0x0000000100104cf0
symbol = 0x0000000100104cf0 "?L\x10"
}
tag = ConsCell
}
But if p operator, I get:
(lldb) p operator
error: expected a type
error: 1 errors parsing expression
However, using frame variable operator works:
(lldb) frame variable operator
(Value) operator = {
data = {
number = 1068208
list = 0x0000000100104cb0
symbol = 0x0000000100104cb0 "\x10L\x10"
}
tag = ConsCell
}
What's going wrong when I'm using p operator?
lldb evaluates expression in hybrid of C++ and Objective-C. operator, the name of your variable, is a reserved keyword in C++. When you use the p command (which is an alias to expression command), lldb passes your expression to clang to parse and evaluate in C++/Objective-C (or, if you're debugging a Swift method, parse and evaluate in Swift). Even though your program is written in straight C, your expressions are evaluated as C++ expressions and that's not a valid C++ expression.
frame variable (fr v for short) doesn't go through a compiler for evaluation, it tries to do simple parsing of the variable path provided. It can do simple dereferencing and following of pointers, but it can't cast values for instance.