"break" and "continue" in Emacs Lisp

"break" and "continue" in Emacs Lisp

[Herbert Euler]

Hello,

I don't know how to write an Emacs Lisp program that's equal
to the following C program, because of break and continue:

    i = 0;
    while (i++ < 100)
        if (i == 25)
            continue;
        else if (i == 75)
            break;

For break, I now write it in this way:

    (let ((i 0))
      (while (and (< i 100) (not (eq i 75)))
        () ; operations here
        (setq i (1+ i))))

Perhaps catch and throw also work.

For continue, this can work:

    (let ((i 0))
      (while (< i 100)
        (if (not (eq i 25))
            () ; operations here
          ())
        (setq i (1+ i))))

I don't think this is clear and straightforward. Is there any better
solution? Is there no goto in Emacs Lisp?

Thanks in advance.

Regards,
Guanpeng Xu

_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today it's FREE! 
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/

Re: "break" and "continue" in Emacs Lisp

[Pascal Bourguignon]

"Herbert Euler" <herberteuler@hotmail.com> writes:

> Hello,
>
> I don't know how to write an Emacs Lisp program that's equal
> to the following C program, because of break and continue:
>
>     i = 0;
>     while (i++ < 100)
>         if (i == 25)
>             continue;
>         else if (i == 75)
>             break;
>
> For break, I now write it in this way:
>
>     (let ((i 0))
>       (while (and (< i 100) (not (eq i 75)))
>         () ; operations here
>         (setq i (1+ i))))
>
> Perhaps catch and throw also work.

(require 'cl)
(loop with i = 0
      while (< (incf i) 100)
      do (unless (= i 25)
           (when (= i 75) (return))
           (princ i) (princ " ")))

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 26 27
28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73
74


> For continue, this can work:
>
>     (let ((i 0))
>       (while (< i 100)
>         (if (not (eq i 25))
>             () ; operations here
>           ())
>         (setq i (1+ i))))
>
> I don't think this is clear and straightforward. Is there any better
> solution? Is there no goto in Emacs Lisp?

No, not in emacs lisp.

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/

In a World without Walls and Fences, 
who needs Windows and Gates?