Re: future of annotations in Lua?

[Roberto Ierusalimschy <roberto@...>]

> [...]
> that using '<' like that would introduce ambiguites that would
> preclude general function annotations in the commonly-adopted
> annotation style. The following would be hard to parse without
> significant lookahead:
> 
>    local x = y
> 
>    <my_custom_annotation(with, arguments)>
>    function my_global_function()
>       -- ...
>    end
> 
> If the door is to be left open for such a generalized mechanism in
> future versions of Lua beyond 5.4, then adopting a syntax based on an
> unused token such as @annotation would be advisable. Matching the
> annotation syntax of other languages would be a side benefit.

There is a big difference between all those syntaxes and the one
we are using in Lua, not because of the peculiarities of '<name>'
versus '@name': They are all prefixed to the whole item to which they
apply. Following their syntax, we should write '@toclose local x = 1',
instead of 'local @toclose x = 1'.

For locals it is not a big difference, but the following looks weird to
my eyes, no matter the details:

     @my_custom_annotation(with, arguments)
     function my_global_function()
        -- ...
     end

Maybe it is a consequence of Lua not having explicit statement
termination, but I do not visualy associate the attribute to the
function. They look like two independent statements. (BTW, note that
the C++ [syntax] in Lua would have the same problem that <name>,
assuming prefixed attributes.)

-- Roberto