is_array.lua

-- my usual implementation

local is_posint = function(k)
    return (type(k) == "number") and (k > 0) and (k % 1 == 0)
end

local is_array = function(t)
    local n, nmax = 0, 0
    for k,_ in pairs(t) do
        if is_posint(k) then
            if k > nmax then nmax = k end
        else return false end
        n = n+1
    end
    return n == nmax
end

-- from http://ericjmritz.name/2014/02/26/lua-is_array/

function is_array(t)
    local i = 0
    for _ in pairs(t) do
        i = i + 1
        if t[i] == nil then return false end
    end
    return true
end