it's what you use to pass by reference ..... but algol supports pass-by-name semantics (of which pass by reference is an optimisable subset) - to do fill pass b

it's what you use to pass by reference ..... but algol supports pass-by-name semantics (of which pass by reference is an optimisable subset) - to do fill pass by name (for a simple example a[i] where i is a global) the compiler will create a thunk (a tiny subroutine, in scope of the place where the parameter was passed) and pass a pointer to it - the tag of '7' means a PCW - when it gets dereferenced as a pointer the hardware does a subroutine call to the thunk in the correct scope