Pascal Costanza  <pc@p-cos.net> wrote:
+---------------
| The general structure of a DO form is this:
| 
| (do ((var1 init1 expr1)
|       (var2 init2 expr2)
|       ...)
|      (predicate [result])
|    body ...)
| 
| This is equivalent to the following LOOP form:
| 
| (loop for var1 = init1 then expr1
|        for var2 = init2 then expr2
|        ...
|        until predicate
|        ; or:
|        when predicate return result
|        do body ...)
| 
| There is no real difference...
+---------------

Incorrect. These two are actually *semantically* different!!
To make them the same, you need to use AND instead of all but
the first FOR:

  (loop for var1 = init1 then expr1
	AND var2 = init2 then expr2
	...
	when predicate return result
	do body ...)

Alternatively, you could have used your "all FORs" version
of the LOOP but replaced DO by DO*, then they would have also
been the same [but still different from the other DO/LOOP pair].

+---------------
| Compare:
| (loop for var1 in list1
|        for var2 = init2 then expr2
|        for index from 0
|        do body ...)
| 
| with:
| (do ((tail1 list1 (cdr tail1))
|       (var2 init2 expr2)
|       (index 0 (1+ index))
|      ((null tail1))
|    (let ((var1 (car tail1)))
|      body ...))
+---------------

Again these are different: You need to either (1) use DO* for the
second or (2) in the LOOP replace all FOR except the first with AND.
Warning: (1) & (2) can give different results, depending upon the
form EXPR2!!

+---------------
| Really, there is no reason not to switch to LOOP when you usually use DO.
+---------------

I agree!! But when you do, at least get the semantics right...  ;-}  ;-}


-Rob

-----
Rob Warnock			<rpw3@rpw3.org>
627 26th Avenue			<URL:http://rpw3.org/>
San Mateo, CA 94403		(650)572-2607