[fpc-devel] new features and facilities

[Mark Morgan Lloyd]

Michael Van Canneyt wrote:
> On Thu, 8 Oct 2015, Sven Barth wrote:
> 
>> Am 08.10.2015 19:10 schrieb "Ralf Quint" <freedos.la at gmail.com>:
>>>
>>> On 10/8/2015 9:54 AM, Sven Barth wrote:
>>>>
>>>>
>>>> I had the idea to implement inline-if as well. I think the syntax I
>> selected is derived from Oxygene, but it looks very Pascal and shouldn't
>> break anything:
>>>>
>>>> left := if expr1 then expr2 else expr3;
>>>>
>>>> Thereby expr1 returns Boolean and expr2 determines the type of the 
>>>> whole
>> inline-if, thus expr3 needs to be compatible to expr2.
>>>>
>>>>
>>> Sorry, but that doesn't "look Pascal" at all, and is anything but easily
>> understandable, specially given the possible complexity of expr[1,2,3]...
>>
>> And you think C's ternary would be more Pascal? Also you need /some/
>> definition of what defines the type no whether what syntax you choose (in
>> addition expr1 is the same as in normal ifs, so it's only the 
>> "complexity"
>> of expr2 and expr3). And no, "the left side" is not the Pascal answer
>> either.
> 
> Actually, yes I think C's or Javascript's ternary is better suited.
> 
> Let me explain. If I see
> 
> If expr1 then expr2 else expr3
> 
> it says 'statement' to me. But
> 
> a ? b : c;
> 
> Says "expression" to me.
> 
> So
> 
> left := a ? b : c;

OK. So presumably, since false < true, b is executed if a is false and c 
is executed if it's true? >:-)

> looks more 'right' than the 'if then else', because the right-hand side 
> is clearly an expression.
> 
> The "if expr1 then expr2 else expr3" is equally counter-intuitive and 
> confusing as anonymous functions.
> 
> Keyword "If" starts a statement. If you allow to use it in expressions, 
> its meaning becomes context sensitive. That is a bad thing in my book.
> 
> So if this thing needs to be implemented, then I'd much prefer it in the 
> ternary form.

The way I look at it is that it's restoring a feature that was (possibly 
accidentally) dropped during the ALGOL -> Pascal transition. As such I 
don't have any problem with ALGOL-style

left := if a then b else c;

After all, while concise C-style operators work well in expressions this 
is not a simple expression where all components are evaluated: it's 
directly equivalent to the statement-level  if  potentially including 
exactly the same short-circuiting rules in the boolean expression (a above).

The thing I do have problems with is the difficulty people had 
explaining nested inline ifs during the 1960s. However I think that was 
more because they simply hadn't worked out how to write language 
documentation rather than there being anything inherently tricky about 
it, and these days there's absolutely no reason why it shouldn't be 
spaced and indented in a thoroughly Pascal-like fashion :-)

-- 
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]