Re: Opposite of ~^ FORMAT Directive

vy <volkan.yazici@xxxxxxxxx> writes:

Is it possible to make FORMAT print a phrase just in the first element
of a ~{...~} list iteration. (Like opposite of ~^.)

I think the reason there's not is that often one just reorganizes the
text slightly, pushing the first part out of the loop to the left. e.g.,

(defun foo (x) (format t "First ~{~A~^, then ~}." x))
=> FOO

(foo '(a b c d))
First A, then B, then C, then D.
=> NIL

If the case of (foo '()) is something you worry about, then use:

(defun foo (x) (format t "~:[None~;~:*First ~{~A~^, then ~}~]." x))
=> FOO

(foo '())
None.
=> NIL

If you insist on pushing things into the loop, about the only trick that
comes to mind, and it's really an ugly trick--but worth knowing, is to
use some sort of circular list thing, as in:

(defun circular-list (&rest args)
(let ((x (copy-list args)))
(nconc x x)))
=> CIRCULAR-LIST

(setq *print-circle* t)
=> T

; test it out
(circular-list 'a 'b 'c)
=> #1=(A B C . #1#)

(defun foo (x)
(format t "~:{~:[First~:;then~] ~A~:^, ~}."
(mapcar #'list ;this mapcar will stop as long as x is not circular!
(cons nil (circular-list t))
x)))
=> FOO

(foo '(a b c d))
First A, then B, then C, then D.
=> NIL

Then again, I don't use every last feature of FORMAT, so maybe someone else
remembers another feature I'm forgetting.

But you know, you're not really _required_ to put everything in one FORMAT
string. It is ok to use conventional loops, multiple calls to FORMAT, etc.
Sometimes, it's a lot more readable that way, too.
.

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