Added some cases to the noun inflector (issue #500) (#593)

* Added some cases to the noun inflector (issue #500)

* Some spaces in comments

* Whitespace

lib/natural/inflectors/noun_inflector.js

@@ -87,6 +87,56 @@ const NounInflector = function () {
   this.pluralForms.regularForms.push([/^(?!talis|.*hu)(.*)man$/i, '$1men'])
   this.pluralForms.regularForms.push([/(.*)/i, '$1s'])
 
+  // Words ending in -ff or -ffe you just add s to make the plural.
+  // Sheriffs | Giraffes
+  // this.pluralForms.regularForms.push([/(.+ffe?)$/i, '$1s'])
+
+  // words ending in f that just add s:
+  // roof - roofs
+  // chief - chiefs
+  // oaf -oafs
+  // this.pluralForms.regularForms.push([/([^f]+f)$/i, '$1s'])
+
+  // Example of words using the -f / -fe to -ves rule
+  // leaf - leaves
+  // wolf - wolves
+  // calf - calves
+  // half - halves
+  // knife - knives
+  // loaf - loaves
+  // life - lives
+  // wife - wives
+  // shelf - shelves
+  // thief - thieves
+  // yourself - yourselves
+  this.addIrregular('leaf', 'leaves')
+  this.addIrregular('wolf', 'wolves')
+  this.addIrregular('calf', 'calves')
+  this.addIrregular('half', 'halves')
+  this.addIrregular('knife', 'knives')
+  this.addIrregular('loaf', 'loaves')
+  this.addIrregular('life', 'lives')
+  this.addIrregular('wife', 'wives')
+  this.addIrregular('shelf', 'shelves')
+  this.addIrregular('thief', 'thieves')
+  this.addIrregular('yourself', 'yourselves')
+
+  // Some words have multiple valid plural forms endings with -ves or -s:
+  // scarf - scarfs/scarves
+  // dwarf - dwarfs / dwarves
+  // wharf - wharfs / wharves
+  // handkerchief - handkerchiefs / handkerchieves
+  // this.pluralForms.regularForms.push([/(.*r)f/i, '$1ves'])
+
+  // Singular inflections
+
+  // Some words have multiple valid plural forms endings with -ves or -s:
+  // scarf - scarfs/scarves
+  // dwarf - dwarfs / dwarves
+  // wharf - wharfs / wharves
+  // handkerchief - handkerchiefs / handkerchieves
+  this.singularForms.regularForms.push([/(.*)ves$/i, '$1f'])
+
   this.singularForms.regularForms.push([/([^v])ies$/i, '$1y'])
   this.singularForms.regularForms.push([/ives$/i, 'ife'])
   this.singularForms.regularForms.push([/(antenn|formul|nebul|vertebr|vit)ae$/i, '$1a'])