anagram.exs

defmodule Anagram do

  ####
	# given a word, return a list of anagrams

	def anagrams_of(word) do
	  Keyword.get(dictionary, signature(word), [])
	end


	###
	# Read in a dictionary file, and return a keyword list where
	# the key is the signature of a word, and the value is a 
	# list of all the words sharing that signature

	def dictionary do
		word_list |> make_signatures |> hashify_dictionary
	end

	def word_list(from // "/usr/share/dict/words") do
	  IO.puts("start word list")
	  result = case File.read(from) do
		  { :ok, all_words } ->
	  	      String.split(all_words, [" ", "\r", "\n"], [])
	  end
	  IO.puts("end word list")
	  result
	end

	# Given a list of words, return a list of [ signature, word ]

	def make_signatures(words) do
	  IO.puts("start make_signatures")
	  result = lc word inlist words, do: [ signature(word), word ]
  	  IO.puts("end make_signatures")
  	  result
	end

	# the signature is the letters in the word, sorted

	def signature(word) do
		String.codepoints(word) |> Enum.sort |> list_to_binary |> binary_to_atom(:utf8)
	end

	###
	# take a list of [ signature, word ] and create a hash
	# where the key is the signature and the value is
	# a list of all words with that signature

	def hashify_dictionary(list) do
		Enum.reduce list, [], fn([signature, word], hash) ->
		  case Keyword.get(hash, signature) do
			nil  -> Keyword.put(hash, signature, [ word ])
			list -> Keyword.put(hash, signature, [ word | list ])
  		  end
 	    end
	end
end