metamethod __lt oddity?

[Gunnar Zötl <gz@...>]

Hello,

I did some more experiments with metatables and metamethods, and came
across something I would consider curious. Consider this piece of
code:

  function get_op_args(op1, op2)
        if type(op1) == "number" then op1 = { val=op1 } end
        if type(op2) == "number" then op2 = { val=op2 } end
        return op1, op2
  end

  mt = {
        __add = function(op1, op2)
                op1, op2 = get_op_args(op1, op2)
                return op1.val + op2.val
        end,
        __lt = function(op1, op2)
                op1, op2 = get_op_args(op1, op2)
                return op1.val < op2.val
        end
  }

  t = { val = 17 }
  setmetatable(t, mt)

now there is a table t that can be added and compared. Some tests show
that:

  print(t + 4)         --> 21
  print(4 + t)         --> 21
  print(t < {val=4})   --> false
  print({val=4} < t)   --> true

work well and yield the expected result. However, neither of these
works:

  print(t < 4)
  print(4 < t)

The error I get is "lua: metamethods.lua:27: attempt to compare table
with number". From the documentation it would seem that this should
work, just as t+4 does. Or am I missing something?

rgds,

Gunnar