Re: language design after Algol 60

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.

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