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On 08/01/2015 20:15, Roberto Ierusalimschy wrote:

I already asked the opinion of Lua Team about this when work2 came
out, I got some remarks from lua-l members, but I got no "official"
response, so I dare bump it up.

A couple of features I'd like to see implemented would be:

1. Binary literals, such as 0b100101101, or something like that.

2. A non-significant digit separator (say "_") for better
readability of long numbers:

1111_222_333_4444 would be parsed (lexed?) as 1111222333444,
of course banning the underscore from the beginning and the end.

Even more useful for 64bit hex literals or binary literals (if implemented):

0xaabef_bee1_1230_aabb
0b1001_1100_1111_001_1_111

(useful when representing some register or binary data structure layout).

The digit separator thing seems almost zero-cost (skip a char in the
lexer, I guess). Binary literal may be a little more expensive, but
since tonumber already handles the translation in the language,
maybe some code reuse under the hood could make this change very
lightweight.

Do Lua Team think they could be added to a next version? I think the
convenience is very high (now that "bit fiddling" in Lua has been
graced with 64bit ints and binops) with very few drawbacks.


First, we disagree that the convenience is "very high". (I would
give it at most a "medium". :-)


Fair point. Overenthusiastic hyperbole! :-)


Of course, for some people it may be
the most important feature of the language, but this is true for almost
anything that people ask. (It is also important to measure the
convenience as compared with the alternatives already presented
in previous discussions.)

Also, the costs are not as low as it sounds. Among other points, we have
to consider the following:

- Should "tonumber" also support these features? (If so, the
implementation is not as trivial as it sounds.)

- Should io.read("n") support them? (Again, more work ahead.)
Ok. Good to know. I thought there were more code commonality among the conversion routines in the lexer and in library functions, so I thought it would have been easy to add all the code almost in one place. 


- If Lua is going to support binary numerals, shouldn't it have some way
to print them? ("%b" in string.format is more work, specially if we are
going to support flags, width, and precision, like the other formats.)
Mmmh. IIRC string.format relies on underlying C printf family functions (does it?), so I see it could be difficult to add a new format specifier on top of that. I think we could live without that. I find the convenience of the features I mentioned is higher when writing expressions and constants, rather than in I/O. 


(Not to mention that binary numbers could also ignite the anger of
octal-lovers :-)


Argh! NO! NO! stop binary numbers if this will stop those pesky octals! :-D



-- Roberto




Thanks for the prompt reply!

Cheers!

-- Lorenzo