simple pluralization framework

pluralize.rb

module Pluralize
  module_function

  def pluralize(string)
    string = string.dup

    @plural.each do |pattern, options|
      string.gsub!(pattern, options[:replace])
    end

    string
  end

  def singularize(string)
    string = string.dup

    @singular.each do |pattern, options|
      string.gsub!(pattern, options[:replace])
    end

    string
  end

  @singular, @plural = {}, {}

  def singular(pattern, options)
    @singular[pattern] = options
  end

  def plural(pattern, options)
    @plural[pattern] = options
  end

  ## Regular Plurals
  #
  # The plural morpheme in English is suffixed to the end of most nouns.
  # Regular English plurals fall into three classes, depending upon the sound
  # that ends the singular form:
  #
  # Where a singular noun ends in a sibilant sound—/s/, /z/, /ʃ/, /ʒ/, /tʃ/,or
  # /dʒ/—the plural is formed by adding /ɨz/. The spelling adds -es, or -s if
  # the singular already ends in -e:
  #
  # kiss     kisses    /ˈkɪsɨz/
  # phase    phases    /ˈfeɪzɨz/
  # dish     dishes    /ˈdɪʃɨz/
  # massage  massages  /məˈsɑːʒɨz/ or /ˈmæsɑːʒɨz/
  # witch    witches   /ˈwɪtʃɨz/
  # judge    judges    /ˈdʒʌdʒɨz/

  plural /ss$/, replace: 'sses'
  plural /se$/, replace: 'ses'
  plural /sh$/, replace: 'shes'
  plural /ge$/, replace: 'ges'
  plural /ch$/, replace: 'ches'
  plural /ge$/, replace: 'ges'

  # When the singular form ends in a voiceless consonant (other than a sibilant) — /p/, /t/, /k/, /f/ or /θ/, — the plural is formed by adding /s/. The spelling adds -s. Examples:
  # lap    laps    /læps/
  # cat    cats    /kæts/
  # clock  clocks  /klɒks/
  # cuff   cuffs   /kʌfs/
  # death  deaths  /dɛθs/
  plural /ap$/, replace: 'aps'
  plural /at$/, replace: 'ats'
  plural /ck$/, replace: 'cks'
  plural /ff$/, replace: 'ffs'
  plural /th$/, replace: 'ths'

  # For all other words (i.e. words ending in vowels or voiced non-sibilants) the regular plural adds /z/, represented orthographically by -s:
  # boy    boys    /bɔɪz/
  # girl   girls   /ɡɜrlz/
  # chair  chairs  /tʃɛərz/
  plural /y$/, replace: 'ys'
  plural /l$/, replace: 'ls'
  plural /r$/, replace: 'rs'
end

require 'bacon'
Bacon.summary_on_exit

describe Pluralize do
  def pluralize(string)
    Pluralize.pluralize(string)
  end

  it 'pluralizes words ending with sibilant sound' do
    pluralize("kiss").should == "kisses"
    pluralize("phase").should == "phases"
    pluralize("dish").should == "dishes"
    pluralize("message").should == "messages"
    pluralize("witch").should == "witches"
    pluralize("judge").should == "judges"
  end

  it 'pluralizes words ending with consonant sound' do
    pluralize('lap').should == 'laps'
    pluralize('cat').should == 'cats'
    pluralize('clock').should == 'clocks'
    pluralize('cuff').should == 'cuffs'
    pluralize('death').should == 'deaths'
  end

  it 'pluralizes words ending in vowels or voiced non-sibilants' do
    pluralize('boy').should == 'boys'
    pluralize('girl').should == 'girls'
    pluralize('chair').should == 'chairs'
  end
end