Number literals (Was: Re: Case Range Statement ..)

[Andrei Alexandrescu]

Rainer Deyke wrote:
> Andrei Alexandrescu wrote:
>> Derek Parnell wrote:
>>> I would not complain if trailing dot and leading dot were disallowed.
>> I think the question that should be asked is: would anyone complain if
>> they were kept? We have bigger rocks to move than that one.
> 
> It seems rather disingenuous to complain loudly about '...' used as a
> separator, but to accept leading/trailing dots without question.

Well it's rather congruent. The leading and trailing dots have been in 
the language for a good while and haven't caused major problems. So I am 
not bent on eliminating them. On the other hand, I don't feel like 
throwing ellipses in the mix just to make things more confusing.

> I'm
> sure you remember this list:
> 
>> 0.....wyda
>> 0....wyda
>> 0... .wyda
>> 0. .. .wyda
>> 0.... wyda
>> 0. ...wyda
>> 0. ....wyda
>> 0.. .wyda
> 
> I'm sure you agree that this is a mess.

I do.

> Never mind if any of these
> token sequences are syntactically valid, this is a mess at the lexical
> level.

They all are parsable if ellipsis is to be allowed as separator. Not at 
all. They are very easy to parse lexically. It's the humans who have 
problems.

> If '0.....wyda' is interpreted as the token sequence '0. ... .
> wyda', then you have bigger things to worry about than whether or not
> that token sequence is ever syntactically valid.

What you describe is standard lexing. The sequence 0.....wyda is lexed 
using maximum munch (the longest thing that looks like a token is chosen 
left to right). First we have a 0 and so the longest token is 0. Then 
follow four dots, but a maximum of three form a token. Finally, we have 
.wyda which is a token. And that's about it. The rule is not 
complicated, but of course having to count the dots and exacerbating the 
importance of whitespace placement is undesirable.


Andrei