Extracts the operand at the specified zero-based position, where expr = (op0 op1 op2 ...). cad(n)r foo = cad(n-1)r cdr foo and cad(0)r foo = car foo
A Cons expression for which the nth operand is sought.
The zero-base operand index. MUST be an integer >= 0.
Extracts the operand at the specified zero-based position, where expr = (op0 op1 op2 ...). cad(n)r foo = cad(n-1)r cdr foo and cad(0)r foo = car foo