Re: Overloading and extending operators

[Mike Pall <mikelu-0704@...>]

Hi,

Joe Krahn wrote:
> Is anyone else thinking about or working on something like this?

I posted some ideas about this, inside some other discussion on
efficiency:
  http://lua-users.org/lists/lua-l/2006-09/msg01019.html

BTW: If you don't care too much about efficiency then check out
this simple hack:

  local sm = setmetatable
  local function infix(f)
    local mt = { __sub = function(self, b) return f(self[1], b) end }
    return sm({}, { __sub = function(a, _) return sm({ a }, mt) end })
  end

Now you can define your own named infix operators:

  local shl = infix(function(a, b) return a*(2^b) end)

  print(5 -shl- 4)
  --> 80

Cute, huh? Advantage: no changes to the Lua core needed.
Drawback: one table allocation per operation.

[Credits: this mimicks a similar Python hack:
 http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/384122
]

Bye,
     Mike