Re: boolean operators

[Nick Gammon <nick@...>]

> May I ask you (and others) why you need boolean operators in Lua?

You haven't specified if you mean literally "operators" like >> and  
<< in C, or simply to imbed a bitwise manipulation library in the  
standard distribution.

I think you can make 5 major cases for some sort of bitwise operation  
in the default implementation:


1. To interface with the host program, which may need you to set or  
test individual bits

2. To do calculations (like checksums, encryption) which are defined  
in terms of XOR and similar.

3. Most script languages other than Lua support bitwise operations.

4. Extending the language (by using loadlib etc.) is not always  
possible for the end-user.

5. It is easy to do.


Interface with host
-------------------

One of the major features of Lua is its use as an imbedded script  
language. Thus, the needs of the host need to be taken into  
consideration. There are many cases where the host may need flags set  
or tested. For example, interfacing with a GUI operating system, you  
may have a bit set to indicate if the Ctrl or Shift key is pressed.

Also when calling the host program's functions you may need to set or  
clear individual bits.

Certainly, host program developers can extend Lua by adding their own  
"bit" library, but really, bit manipulation could easily be regarded  
as a "core need" and not require every developer to roll their own  
bit library.

Bitwise calculations
--------------------

A while back I was planning to implement AES encryption using pure  
Lua, but the fact that almost every encryption and hash algorithm  
requires bitwise XOR, OR, and AND operations, this would have been  
very tedious in Lua. It is *possible*, by converting numbers to  
strings and back, but the results would surely be appallingly slow  
(and hard to read). I could have loaded in a bit library to do the  
bit manipulation, but if you are going to do that, you may as well  
load in an encryption library itself, and bypass the bit library  
altogether.

Other script languages
----------------------

As far as I can make out, various "competing" script languages have  
bit manipulation supplied as standard (eg. VBscript, Perlscript,  
Javascript).

Extension not always possible
-----------------------------

There are various implementations of Lua around which make it  
difficult or impossible for the end-user to do things like  
package.loadlib, for security reasons. They don't want their users to  
run arbitrary code. Thus the option of loading in an external bitwise  
library is not always available.

Easy to do
----------

If you simply add Reuben Thomas's bit library to the standard  
distribution, it is only about 60 lines of code (half of which are  
#defines). If a Lua user is desperate for space, they can omit it in  
custom versions, however the default distribution can surely spare  
that minor extra code?


--------------

An alternative to simply incorporating the library as standard would  
be to actually modify the parser and virtual machine to handle bit  
operations inline (eg. a = b >> 4). This would add speed no doubt,  
but be more work overall. Personally I would be happy if the bitwise  
operations were available either way - library or as direct operators.

- Nick Gammon