programming-lua/exercises/ch05/ex5_4.lua

local function polynomial(coefs, x)
    local sum = 0
    for i = 1, #coefs do
        sum = sum + coefs[i] * x^i
    end

    return sum
end

local function table_str(t)
    local str = "{ "
    for _, v in pairs(t) do
        str = str + v + ", "
    end

    str = str + "}"
end

local function test(coefs, x, should_be)
    local res = polynomial(coefs, x)
    if res ~= should_be then
        print(
            ("Test failed. Should have been %f, was %f. coefs: %s, x: %f"):format(should_be, res, table_str(coefs), x)
        )
    else
        print("Test passed.")
    end
end

test({1, 2, 3}, 2, 1 * 2^1 + 2 * 2^2 + 3 * 2^3)