In a Warren's Abstract Machine, where are Argument Variables created?

Question

I'm trying to create my own WAM implementation and I'm using the instructions in Figure 2.10 of "Warren's Abstract Machine: A Tutorial Reconstruction" as a test case. However, I need to pass A1 and A2 to get_structure. But where are both variables created? put_value and put_variable both create A-variables but neither is listed in the instructions.

Answer 1

A_i are "argument registers". They are part of the machine. So put_value does not create them, it fills them. Figure 2.8 on page 23 says:

put_value X_n, A_i ===  A_i <- X_n

meaning, store the value X_n in A_i.