programming-lua/exercises/ch05/ex5_6.lua

local function is_sequence(t)
    local prev_k = 0
    for k, _ in pairs(t) do
        if type(k) ~= "number" or k ~= prev_k + 1 then
            return false
        end

        prev_k = prev_k + 1
    end

    return true
end

local function table_str(t)
    local str = "{"
    for k, v in pairs(t) do
        if type(k) == "string" then
            k = '"' .. k .. '"'
        end
        str = ("%s [%s] = %s,"):format(str, k, v)
    end

    str = str .. " }"

    return str
end

local function test(t)
    print(("%s: %q"):format(table_str(t), is_sequence(t)))
end

test({ 1, 2, 3, word = "a word", [10] = 999 })
test({ 1, 2, 3 })
test({ [1.0] = 1, [2] = 2 })
test({ [1.1] = 1, [2] = 2 })