Another take on locals by default.

[Pierre-Yves Gérardy <pygy79@...>]

I just stumbled on LiveScript (http://gkz.github.com/LiveScript/), yet
another CoffeeScript fork.

The language has locals by default, and has an interesting solution to
the local/upvalue definition and assignment conundrum.

`a = 5` is always a local assignment. a is declared as local if it
wasn't already. To assingn to an upvalue, you use the := operator.
The language doesn't have globals. Transposed to Lua, this would be.

    make_incr = function()
      acc=0 --local, by default
      return function()
        acc = acc + 1
        -- a local acc shadows the upvalue.
        -- this always add 1 to nil, or 1 to 0,
        -- depending on when you decide to declare the local,
        -- before or after the evaluation of the right hand side.
        return acc
      end
    end

    incr= make_incr()
    incr() --> 1
    incr() --> 1


    -- This works as intended
    make_incr = function()
      acc=0 --local, by default
      return function()
         acc := acc + 1 -- upvalue assignment
         return acc
      end
    end

Marking assignment to non-locals explicit makes IMO the code easier to read.
Globals could use yet another token.

This would prevent a lot of bugs, and make strict.lua obsolete.
If not for Lua, this could be a nice improvement in MoonScript.

Kind regards,
-- Pierre-Yves