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From: Andy Walker <anw@cuboid.co.uk>
Newsgroups: comp.compilers
Subject: Re: language design after Algol 60
Date: Sun, 15 Apr 2018 00:04:13 +0100
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Keywords: algol68, design
Posted-Date: 14 Apr 2018 21:03:31 EDT
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On 14/04/18 05:19, Robin Vowels wrote:
> From: "bartc" <bc@freeuk.com>
[...]
>> Then by leaving out the bits not needed you end up with this:
>>     to n do ...
> The control variable, i, must not be omitted.

	Can't answer for Python [the previous topic] or for BartC's
own languages, but in Algol 68, as Bart referenced, it most certainly
can, and sometimes ought to be.

	Specific examples:

   (a) Sometimes the control variable does not proceed by constant
increments:

       int i := 0;
       to n do ...;  i +:= f(i) od

   (b) Sometimes the control variable, if present, might overflow, eg in
       the case of a loop that goes round more than "maxint" times:

       while ... do ... od

       [May be worth noting that RR3.5.2 Step 4 contains a bug in the
        printed version in this case, pointed out and corrected somewhere
         in "Algol Bulletin".  You could write "for i by 0 to 2 ..." but
        that is just silly.]

> It may be required for computations within the loop
> (including subscript references).

	And it may not.  Programmer's decision.

> Even if not explicitly referenced within the loop,
> its value will be required for fault finding (with error control
> and/or with debugger).

	*May* be.  Depends on the "error control" and "debugger", and
how they, if they exist, interact with the programmer, on what faults
may have occurred -- perhaps the code was already tested -- and on
the phase of the moon.

	Personally, I'm not a big fan of the style police, nor of
languages that encourage them.

--
Andy Walker,
Nottingham.