Re: Lightweight function syntax: no need to change Lua

[Dirk Laurie <dpl@...>]

On Sun, Nov 28, 2010 at 10:35:31AM +0200, Dirk Laurie wrote:
> The following syntax:
> 
>     ('a,b,c')('a+b+c') == function(a,b,c) return a+b+c end
> 
> is available after doing this chunk:
> 
>     getmetatable("").__call = 
>       function(arg,res)
>         if #arg>0 then return load(arg.."=...; return "..res)
>         else return load("return "..res)
>         end
>       end
> 
Someone said, giving no example, that this will not work
for all closures.  I've found one reason: the function 
messes up global variables with the same names.

Improvement (tested under the current Lua 5.2 alpha):

--[[ In a package file ]]
_mapsto = 
  function (arg,res)
    if #arg>0 then return load("local "..arg.."=...; return "..res)
    else return load(res)
    end
  end

--[[ In the user's program ]]
getmetatable("").__call = _mapsto

It allows monstrosities like:

> return ('x,y')('x+y,x-y')(5,2)
7   3

Do I really want people to perpetrate such things and still claim 
they're writing Lua?  Food for thought.

Dirk