In the for-as-in-list subclause,
the for
or as construct iterates over the contents of a
list. It checks for
the end of the list as if by using endp.
The variable var is bound to the successive elements of
the list in form1 before each
iteration. At the end of each iteration, the function step-fun
is applied to the list; the default value for step-fun is
cdr.
The loop keywords in and by serve as valid prepositions in
this syntax.
The for or as construct causes termination when the
end of the list is reached.