words.erl

%% My second code kata.
%% This is the first part of the question listed at this URL:
%%  http://codekata.pragprog.com/2007/01/kata_eight_conf.html
%% more to come later.
-module(words).
-author('OJ Reeves <oj@buffered.io>').
-export([composition/1]).
-define(WORDLENGTH, 6).

composition(FileName) ->
  Words = lists:map(fun string:to_lower/1, file_to_list(FileName)),
  CW = composable_words(Words),
  Results = lists:map(fun(W) -> composition(W, Words) end, CW),
  lists:map(fun show_result/1, Results).

show_result(none) ->
  ok;
show_result({ok, List}) ->
  lists:map(fun({F,B}) -> io:format("~s + ~s => ~s~s~n", [F, B, F, B]) end, List).

composition(Word, Dict) ->
  composition(breakdown(Word), Dict, []).

composition([], _, Accum) ->
  case Accum of
    [] -> none;
    _ -> {ok, Accum}
  end;
composition([Pair={Front,Back}|T], Dict, Accum) ->
  case {lists:member(Front, Dict), lists:member(Back, Dict)} of
    {true, true} -> composition(T, Dict, [Pair|Accum]);
    _ -> composition(T, Dict, Accum)
  end.


file_to_list(FileName) ->
  {ok, Bin} = file:read_file(FileName),
  string:tokens(binary_to_list(Bin), "\n").

composable_words(Words) ->
  lists:filter(fun(Word) -> length(Word) =:= ?WORDLENGTH end, Words).

breakdown(Word) ->
  [_|W] = lists:zip(inits(Word), tails(Word)),
  lists:takewhile(fun({_,X}) -> X =/= [] end, W).

inits([]) ->
  [[]];
inits([H|T]) ->
  Inits = inits(T),
  Tail = lists:map(fun(X) -> [H|X] end, Inits),
  [[]|Tail].

tails([]) ->
  [[]];
tails(List=[_|T]) ->
  [List|tails(T)].