loop translations (was: Re: language translator help)

[John W. Eaton]

On 27-Apr-2002, Neil Jerram <address@hidden> wrote:

| I'm not aware of such a document.  Suggest you post the translation
| code that you've tried already.  I'll certainly take a look, and I
| guess you'll get a deluge of suggestions from others as well.

OK, here goes.

I'd like to understand how to translate some simple loops.  For
example, the following loop is valid in Octave.

  for i = 1:3
    disp (i);
    if (i == 2)
      break;
    endif
  endfor

This should print

  1
  2

Note that this sequence of statements doesn't return any value.  For
Guile, the best I've come up with is

  (let for ((i 1))
    (call-with-current-continuation
     (lambda (break)
       (if (<= i 5)
           (begin
             (display i)
             (newline)
             (if (= i 2)
                 (break (if #f #f)))
             (for (+ 1 i)))))))

This works, but seems quite complex to me.  Is there a simpler way?

Here is another:

  for i = 1:4
    if (i < 4)
      disp ("foo-i-hithere");
      if (i == 2)
        continue;
      endif
    endif
    disp (i);
  endfor

This should print

  foo-i-hithere
  1
  foo-i-hithere
  foo-i-hithere
  3
  4

For Guile, I came up with

  (let for ((i 1))
    (call-with-current-continuation
     (lambda (continue)
       (if (<= i 4)
           (begin
             (if (< i 4)
                 (begin
                   (display "foo-i-hithere")
                   (newline)
                   (if (= i 2)
                       (continue (for (+ 1 i))))))
             (display i)
             (newline)
             (for (+ 1 i)))))))

Again, this works but is there a better way?  It seems undesirable to
duplicate the (for (+ 1 i)) bit.

jwe