Re: Embedded 'nil' values - a suggestion

[Wim Couwenberg <w.couwenberg@...>]

>> It is possible.  See also recent posts about this on this list:
>>
>>   http://lua-users.org/lists/lua-l/2006-02/msg00537.html
>>
>> Specifically the "select("#", ...)" construct.

> Why thank you! Odd, but workable.

As another fun example, define the following functions:


local unpack, select = unpack, select

function pack(...)
  local v = {...}
  local n = select("#", ...)

  return function(f, from, to)
    from = from == nil and 1 or
      from < 0 and n + 1 + from or
      from

    to = to == nil and n or
      to < 0 and n + 1 + to or
      to

    return f(v, from, to)
  end
end

function upairs(v, from, to)
  return function(v, i)
    i = i and i + 1 or from
    if i <= to then
      return i, v[i]
    end
  end, v
end


Examples:

> p = pack("aap", "noot", nil)
> =p(unpack)
aap  noot  nil

> =p(unpack, 1, -2)
aap  noot

> =p(unpack, -2)
noot nil

> for i, v in p(upairs) do print(i, v) end
1  aap
2  noot
3  nil

> for i, v in p(upairs, -2) do print(i, v) end
2  noot
3  nil


--
Wim