Re: Could we have elegant version requirement from 5.3 on?
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- Subject: Re: Could we have elegant version requirement from 5.3 on?
- From: Sean Conner <sean@...>
- Date: 2014年3月26日 03:57:28 -0400
It was thus said that the Great Dirk Laurie once stated:
> There seems to be no way of making Lua code say politely:
> "This program requires Lua 5.3" when running under Lua 5.2.
> Instead, one gets a nasty message like
>
> ./myprog.lua:28: unexpected symbol near '&'
>
> as soon as it hits a bitwise operator.
>
> But maybe it is not late for next time round. We are already
> ignoring one leading `#` line.
I don't think ignoring the leading '#' is done in the parser. I tried
embedding the source code to some Lua code that starts with a shebang line
[1] and loading it with luaL_loadbuffer() [2] and received a parsing error
[3].
> We could equally well ignore
> all leading `#` lines and tag some of them as expressions to be
> asserted _before_ proceeding to lexical analysis of the file.
> This would allow elegant version control and more.
>
> E.g.
>
> #! /usr/bin/env lua
> #@ _VERSION >= 6.0
> #@ bit32
>
> When Lua 5.3 runs this program, or Lua 6.0 runs it without
> having preloaded a bit32 library, the rest of the file would not
> even be looked at.
I thought something like:
#!/usr/bin/env lua -e "if _VERSION ~= 'Lua 5.3' then print('bad lua') return end" -
would work, but apparently not ...
-spc
[1] #!/usr/bin/env lua
[2] Originally, I was precompiling the Lua code, then embedding it:
http://boston.conman.org/2013/03/22.1
http://boston.conman.org/2013/03/23.1
On a lark, I decided to try compressing the actual text instead of
the compiled version, and found it compressed much better.
[3] It's clear that lua and luac toss the first line if it starts with a
shebang [1].