Misfeatures in For loops

[Contestcen at aol.com]

>> GPC accepts the following program, but produces quite silly results:
>>
>> program Foo;
>>
>> var
>>   a: array [1 .. 2] of Integer value (0, 0);
>>   i: Integer;
>>
>> begin
>>   i := 1;
>>   for a[i] := 1 to 10 do
>>     begin
>>       WriteLn (i, ' ', a[i]);
>>       if a[i] = 5 then i := 2
>>     end
>> end.
>>
>> The problem is that it evaluates the index i each time, not once
>> before the loop. It would be possible to fix it, but do we really
>> want that? Neither BP nor CP/EP allow it, they allow only
>> identifiers in for-loops.
>>
>> Waldek and I see no need for such a feature.
> 
> Neither do I.
>
> Nor I.  I vaguely recall that it is forbidden in at least ISO 7185,
> but cannot quote chapter and verse.  This is a milestone, where BP
> is more standards adherent :=)


I have come in late to this discussion, and I am not sure what is the 
supposed "misfeature."  Are the participants saying that Borland Pascal does not 
accept an array element as the control variable of a For loop, and that therefore 
GPC should not accept array elements either?

If that is the case, then the premise is incorrect.  BP does accept array 
elements as control variables.  The following program compiles and runs correctly 
in BP.  It produces the expected result 100.000.

Program  Try;
Var
  a: array[1..10] of integer;
  s: real;
Begin  {Try}
s := 0.0;
for  a[1] := 1 to 10  do
  for  a[2] := 1 to 10 do
    s := s + 1.0;
writeln (s:10:3);
End.  {Try} 

Using array elements as control variables is very useful when you want the 
ability to stop a deeply nested loop, checkpoint the program, and then resume 
the execution from the same point later.  I would not like to see this 
capability removed.

Frank Rubin
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