programming-lua/exercises/ch04/ex4_8.lua

local function remove(str, start, _end)
    local start_part = str:sub(1, start - 1)
    local end_part = str:sub(_end + 1, -1)
    return start_part .. end_part
end

local function remove_patterns(str, pattern)
    while true do
        local rem_start, rem_end, _ = str:find(pattern)
        if rem_start == nil then
            break
        end
        str = remove(str, rem_start, rem_end)
    end

    return str
end

local function ispali(str)
    str = str:lower()

    -- format
    str = remove_patterns(str, "%s")
    str = remove_patterns(str, "%p")

    return str == str:reverse()
end

local function test(str)
    print(("%s: %q"):format(str, ispali(str)))
end

test("step on no pets")
test("banana")

print()

test("Step. On no   pets!")
test("Banana??")