Re: false and nil

[dyngeccetor8 <dyngeccetor8@...>]

On 06/04/2018 11:34 PM, Sam Putman wrote:
>> = true and nil
> nil
>[...]
>> = nil and true
> nil
>[...]
>> = false and nil
> false
> 
> .. Oh. That's not three-valued logic, then. Well at least
> 
>> = nil and false
> nil
> 
> That's... not Abelian either.
> 
> I would like to propose that a future Lua have `false and nil` yield nil,
> and the same for `nil and false`.  This would give an identical semantics
> to the three-valued SQL null[0], and make the trio of values Abelian with
> respect to one another.

Current behavior of "and" and "or" operators is equivalent to
following Lua-like functions.

--[[
  "..." means list of remained arguments.
  "is_empty(...)" means no arguments.
  "process(...)" is some function that will call "f_and" or "f_op"
    for remained elements.
]]

f_and =
  function(first, ...)
    if is_empty(...) then
      return first
    end
    if not first then
      return first
    else
      return process(...)
    end
  end

f_or =
  function(first, ...)
    if is_empty(...) then
      return first
    end
    if first then
      return first
    else
      return process(...)
    end
  end

-- Martin