Scramble Words in Paragraph (Lua)

local function scrambleString(str)
    -- Return a scrambled version of str
    -- using Fisher-Yates shuffle
    local result = ""
    while str:len() > 0 do
        local i = math.random(1, str:len())
        result = result .. str:sub(i, i)
        str = str:sub(1, i - 1) .. str:sub(i + 1)
    end
    return result
end

local function scrambleWords(str)
    return str:gsub("(%w+)", function (word)
        if word:len() > 3 then
            local middle
            repeat
                -- Scramble the middle until it's not the same as the original middle
                middle = scrambleString(word:sub(2, word:len() - 1))
            until middle ~= word:sub(2, word:len() - 1)
            return
                word:sub(1, 1)
                .. middle
                .. word:sub(word:len())
        else
            -- Words 1, 2 or 3 letters long canot be scrambled
            return word
        end
    end)
end

print(scrambleWords([[
When Derek was three, he received his first
pair of pyjama bottoms. When he was five,
he loudly decreed that he would never take
them off. When he reached eight, his parents
realized that Derek wasn't lying. At twelve
he was bullied; at fifteen ignored; at
seventeen, briefly, Derek became a fashion
icon. Now Derek works at home, and his pyjama
bottoms work with him. Theirs is the healthiest
relationship Derek will ever have.]]))