edits.rb

module Edits
  
  def deletes1
    map_transforms do |word, i|
      word.delete_at(i)
    end
  end
  
  def transposes
    map_transforms do |word, i|
      word[i], word[i+1] = word[i+1], word[i]
    end
  end
  
  def replaces
    ("a".."z").map do |c|
      map_transforms { |word, i| word[i] = c }
    end.flatten
  end
  
  def inserts
    ("a".."z").map do |c|
      map_transforms { |word, i| word.insert(i, c) } << "#{self}#{c}"
    end.flatten
  end
  
  def map_transforms
    out = []
    chars = self.split('')
    self.size.times do |i|
      yield(word = chars.dup, i)
      word = word.join
      out << word unless word == self
    end
    out
  end
  
end

String.send(:include, Edits)

describe "a String, imbued with Edits" do
  
  it "works" do
    r = "crap".deletes1
    r.should == %w{ rap cap crp cra }
    
    r = "crap".transposes
    r.should == %w{ rcap carp crpa }
    
    r = "crap".replaces
    r.size.should == 25 * 4
    r.should include( "brap", "frap", "crep", "crop", "crad", "crak")
    
    r = "crap".inserts
    r.size.should == 26 * 5
    r.should include( "zcrap")
    r.should include( "czrap")
    r.should include( "crapz")
  end

  
end