An argument passing convention where the actual argument is
a variable V whose value is copied to a local variable L
inside the called function or procedure. If the procedure
modifies L, these changes will not affect V, which may also be
in scope inside the procedure, until the procedure returns
when the final value of L is copied to V. Under
call-by-reference changes to L would affect V immediately.
Used, for example, by BBC BASIC V on the Acorn
Archimedes.
