Re: Ada standard and maximum line lengths

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 13-01-28 18:42 , Jeffrey Carter wrote:
> On 01/28/2013 01:05 AM, Niklas Holsti wrote:
>> On 13-01-28 08:28 , Jeffrey Carter wrote:
>>
>>> But since the maximum line
>>> length chosen by a compiler also defines the maximum identifier length
>>> accepted by the compiler,
>>
>> Why? I don't see anything in the ARM quote that requires this. The
>> limits on the line length and lexical element length are independent,
>> although they minimum happen to have the same minimum value.
> 
> This isn't addressed directly in the quote. An identifier is a sequence
> of characters from certain classes, terminated by a delimiter; a line
> terminator is a delimiter. In the absence of another restriction on
> identifier length, clearly an identifier cannot be longer than the
> maximum line length.

Agreed.

But the maximum length of an identifier can be *shorter* than the
maximum length of a line. You wrote, above, that the max line length
"defines" the max identifier length. Perhaps you really meant to say
that the max line length sets an upper bound on the max identifier
length, which is true.

>> A compiler could have 200 characters as the maximum lexical element and
>> identifier length, but accept lines of any length, couldn't it?
> 
> Presumably it could. I thought efficiency in compiling was the reason
> behind limiting identifier length

My point is that the compiler's max identifier length can be *less* than
its max line length. Even if a limit on identifier length makes a
compiler more efficient (which I doubt is a significant factor today, at
least if the majority of identifiers are of moderate length), the
compiler could still accept lines of any length, much longer than the
max identifier length.

Returning to the ARM limits, in principle it is necessary to have some
safe lower limits on what a compiler must accept, so that one can be
sure that some strange compiler will not reject one's Ada program just
because it has too long identifiers or lines.

In practice, today this portability could probably work as well based on
informal "usability" criteria -- clearly an Ada compiler with a maximum
identifier length of 10-15 characters (or whatever minimum maximum is
imposed by the predefined identifiers) would often annoy its users.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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