Short form for defining a function (Was: try-catch ...)

[Dirk Laurie <dirk.laurie@...>]

2016-05-31 14:42 GMT+02:00 steve donovan <steve.j.donovan@gmail.com>:
> On Tue, May 31, 2016 at 2:37 PM, Alexey Melnichuk
> <alexeymelnichuck@gmail.com> wrote:
>> May  think  about  short  from to define function.
>
> Believe me, I tried ;)  Such proposals have never flown far.

Maybe because this is already available, though not standardized.

The following code runs on Lua 5.1, Lua 5.2, Lua 5.3 and LuaJIT 2.0.

getmetatable"".__pow =
   function(args,result)
   return (loadstring or load)("local "..args.."=...; return "..result)
   end

print (("x,y,z" ^ "(x-y)/z, (x+y)/z")(3,4,5)) --> -0.2    1.4

The only restriction is that tonumber(args) and tonumber(result)
must be nil. This is no problem for args and can be circumvented
easily for result, e.g. "x,y" ^ "(1)".

In Lua 5.3, I prefer to use other metamethods to allow for default
arguments with the same look.

getmetatable"".__bxor =
   function(args,result)
   return (loadstring or load)("local "..args.."=...; return "..result)
   end

getmetatable"".__bnot =
   function(result)
   return load("local x,y,z=...; return "..result)
   end

> (~"x+y,-x+y")(3,5)  --> 8    2