zl:1 - FTP

183 do
Zetalisp note: Zetalisp supports another, "old-style" version of do. This
form is incompatible with the language specification presented in Guy
Steele's Common Lisp: the Language.
The older do looks like this:
(do var init repeat end-test body . .. )
The first time through the loop var gets the value of the init form; the
remaining times through the loop it gets the value of the repeat form,
which is reevaluated each time. Note that the init form is evaluated before
var is bound, that is, lexically outside of the do. Each time around the
loop, after var is set, end-test is evaluated. If it is non-nil, the do finishes
and returns nil. If the end-test evaluated to nil, the body of the loop is executed.
If the second element of the form is nil, there is no end-test nor exit-forms,
and the body of the do is executed only once. In this type of do it is an
error to have repeats. This type of do is no more powerful than let; it is
obsolete and provided only for Maclisp compatibility.
return and go can be used in the body. It is possible for body to contain
no forms at all.
Examples:
(do (i B (+ 1 i)) ; searches list for Dan.
(names '(Adam Brain Carla Dan Eric Fred) (cdr names)))
I
((null names))
(if (equal 'Dan (car names))
(princ "Hey Danny Boooooy U))) => Hey Danny Boooooy NIL
(do ((22 x (cdr 22)))
((or (null 22)
(2erop (f (car 22))))))
;this applies f to each element of x
;continuously until f returns 2ero.
;Note that the do has no body.
(defun list-splice (a b)
(do ((x a (cdr x))
(y b (cdr y))
(xy 'C) (append xy (list (car x) (car y)))) )
((endp x) (endp y) (append xy x y) ))) => LIST-SPLICE
(list-splice '(1 2 3) '(a b c)) => (1 A 2 B 3 C)
(list-splice '(1 2 3) '(a b c de)) => (1 A 2 B 3 C 0 E)