ipairs_holy(), a range iterator

[askok@...]

Here's a table iterator for 'holy' tables, traversing them 
much like regular ipairs() does.

Can also be used for traversing just a certain range of a 
normal 1..N array.

The approach could be generalized, and a 'step' parameter 
added.  Then it could be a standard 'range()' iterator?
-asko


-----
-- iterator_func [, state, initial_key]= ipairs_range( 
tbl, min_int ,max_int )
--
-- Work like 'ipairs()' but also with tables having range 
other than 1..N and/or holes within them.
--
local function ipairs_range( tbl, first, last )
    --
    -- key, val=
    return function( _, key )
        key= key or first-1
        for newk=key+1,last do
            if tbl[newk] then
                return newk, tbl[newk]
            end
        end
        return nil  -- the end
    end
end

do -- selftest
  local loop= 1
  local values= { {1000,'a'}, {1005,'c'}, {1010,'b'} }

  for n,v in ipairs_range( { [1000]='a', [1010]='b', 
[1005]='c' }, 500, 1200 ) do
    assert( values[loop][1]==n )
    assert( values[loop][2]==v )
    loop= loop+1
  end
--1000    a
--1005    c
--1010    b
end