String Pluralize/Singularize Functions

[Apollos]

I have written two functions to help convert between singular and plural forms of words, particularly for things like monster names. These functions are placed in the file "data/lib/core/string.lua". They can be used to convert all words in a string or just the last word, depending on the second parameter. While I have tested them and they work well for many cases, due to the way English is, they may not always be perfect. Anyways, hope you enjoy.

local vowels = { "a", "e", "i", "o", "u" }

local function pluralizeWord(word)
    if word:match("f$") or word:match("fe$") then
        word = word:gsub("f$", "ves"):gsub("fe$", "ves")
    elseif word:match("ch$") or word:match("sh$") or word:match("s$") or word:match("x$") or word:match("z$") or
    (not string.contains(vowels, word:sub(-2, -2)) and word:match("o$")) then
        word = word .. "es"
    elseif not string.contains(vowels, word:sub(-2, -2)) and word:match("y$") then
        word = word:gsub("y$", "ies")
    else
        word = word .. "s"
    end
    return word
end

string.pluralize = function(str, deepPluralize)
    if deepPluralize then
        local newStr = ""
        for word in str:gmatch("%S+") do
            newStr = newStr .. pluralizeWord(word) .. " "
        end
        return newStr:sub(1, -1)
    else
        return pluralizeWord(str)
    end
end

local function singularizeWord(word)
    if word:match("ives$") then
        word = word:gsub("ives$", "ife")
    elseif word:match("ves$") then
        word = word:gsub("ves$", "f")
    elseif word:match("shes$") or word:match("ches$") or word:match("ses$") or word:match("xes$") or word:match("zes$") or
    (not string.contains(vowels, word:sub(-4, -4)) and word:match("oes$")) then
        word = word:gsub("es$", "")
    elseif not string.contains(vowels, word:sub(-4, -4)) and word:match("ies$") then
        word = word:gsub("ies$", "y")
    else
        word = word:sub(1, -2)
    end
    return word
end

string.singularize = function(str, deepSingularize)
    if deepSingularize then
        local newStr = ""
        for word in str:gmatch("%S+") do
            newStr = newStr .. singularizeWord(word) .. " "
        end
        return newStr:sub(1, -1)
    else
        return singularizeWord(str)
    end
end