Merge pull request #5 from nickkeers/master

Simple parallel algorithm for creating edit lists

check.erl

@@ -5,81 +5,127 @@
 % Read the whole file and makes a list of each word.
 readfile(Filename) ->
   {ok,Binary} = file:read_file(Filename),
-    Words = string:tokens(binary_to_list(Binary), " \v\t\r\n\'\"\\`1234567890-=!@#$%^&*()_+[]{};,./<>?:|"),
-    lists:usort(lists:map(fun(Word) -> string:to_lower(Word) end, Words)).
+  Words = string:tokens(binary_to_list(Binary), " \v\t\r\n\'\"\\`1234567890-=!@#$%^&*()_+[]{};,./<>?:|"),
+  lists:usort(lists:map(fun(Word) -> string:to_lower(Word) end, Words)).
 
-letters() ->	"abcdefghijklmnopqrstuvwxyz".
+letters() ->	
+  "abcdefghijklmnopqrstuvwxyz".
 
 % Form list of words by deleting each letter from the word
 % eg. for "hello" -> ["hell","helo","helo","hllo","ello"]
-deletion_edits(Word) ->	deletion_edits([], Word, []).
+deletion_edits(Word) ->	
+  deletion_edits([], Word, []).
 
-deletion_edits(_, [], Edits) ->	Edits;
-deletion_edits(Before, [Current | After], Edits) ->	deletion_edits([Current | Before], After,[lists:reverse(Before) ++ After | Edits]).
+deletion_edits(_, [], Edits) ->
+	Edits;
+deletion_edits(Before, [Current | After], Edits) ->	
+  deletion_edits([Current | Before], After, [lists:reverse(Before) ++ After | Edits]).
 
 
 % Form list of words by interchanging two consecutive letters of the word
 % eg. for "hello" -> ["helol","hello","hlelo","ehllo"]
-transposition_edits(Word) -> transposition_edits([], Word, []).
+transposition_edits(Word) -> 
+  transposition_edits([], Word, []).
 
-transposition_edits(_, [], Edits) -> Edits;
-transposition_edits(_, [_], Edits) ->	Edits;
-transposition_edits(Before, [Current, Next | After], Edits) ->	transposition_edits([Current | Before], [Next | After],[ lists:reverse(Before) ++ [Next, Current] ++ After | Edits]).
+transposition_edits(_, [], Edits) -> 
+  Edits;
+transposition_edits(_, [_], Edits) ->	
+  Edits;
+transposition_edits(Before, [Current, Next | After], Edits) ->
+  transposition_edits([Current | Before], [Next | After], [ lists:reverse(Before) ++ [Next, Current] ++ After | Edits]).
 
 
 % Form list of words by changing one letter with each of the letters
 % eg. for "me" -> ["ma","mb","mc","..","..","ae","be","ce","..",".."]
-alteration_edits(Word) -> alteration_edits([], Word, []).
+alteration_edits(Word) -> 
+  alteration_edits([], Word, []).
 
-alteration_edits(_, [], Edits) ->  Edits;
-alteration_edits(Before, [Current | After], Edits) ->  BeforeR = lists:reverse(Before),
-                                                        alteration_edits([Current | Before], After, [BeforeR ++ [X] ++ After || X <- letters()] ++ Edits).
+alteration_edits(_, [], Edits) ->  
+  Edits;
+alteration_edits(Before, [Current | After], Edits) ->  
+  BeforeR = lists:reverse(Before),
+  alteration_edits([Current | Before], After, [BeforeR ++ [X] ++ After || X <- letters()] ++ Edits).
 
 
 % Form list of words by inserting each letters in the word at each possible position in the word
 % eg. for "me" -> ["mea","meb","mec","...","...","mae","mbe","mce","...","...","ame","bme","cme","...","..."]
-insertion_edits(Word) -> insertion_edits([], Word, [[X] ++ Word || X <- letters()]).
-
-insertion_edits(_, [], Edits) -> Edits;
-insertion_edits(Before, [Current | After], Edits) -> BeforeR = lists:reverse(Before),
-                                                      insertion_edits([Current | Before], After, [BeforeR ++ [Current, X] ++ After || X <- letters()] ++ Edits).
+insertion_edits(Word) -> 
+  insertion_edits([], Word, [[X] ++ Word || X <- letters()]).
 
+insertion_edits(_, [], Edits) -> 
+  Edits;
+insertion_edits(Before, [Current | After], Edits) -> 
+  BeforeR = lists:reverse(Before),
+  insertion_edits([Current | Before], After, [BeforeR ++ [Current, X] ++ After || X <- letters()] ++ Edits).
 
 % Forms list with all the edits which are possible and filters the elements repeating using "lists:usort"
-edits1(Word) -> lists:usort(deletion_edits(Word) ++ transposition_edits(Word) ++ alteration_edits(Word) ++ insertion_edits(Word)).
-
+edits1(Word) ->
+  Self = self(),
+
+  start_word_workers(Self, Word),
+  %% TODO: Can handle this more gracefully, throw an exception or handle an error tuple or something similar
+  collect(4, Self).
+
+start_word_workers(Collector, Word) ->
+  words_worker(Collector, fun() -> deletion_edits(Word) end),
+  words_worker(Collector, fun() -> transposition_edits(Word) end),
+  words_worker(Collector, fun() -> alteration_edits(Word) end),
+  words_worker(Collector, fun() -> insertion_edits(Word) end).
+
+words_worker(CollectorPid, Fun) ->
+  spawn(fun() ->
+    Words = Fun(),
+    CollectorPid ! {words, Words}
+  end),
+  ok.
+
+collect(N, Parent) ->
+  collect(N, Parent, []).
+
+collect(0, Parent, Acc) ->
+  lists:usort(Acc);
+collect(N, Parent, Acc) when N > 0 ->
+  receive
+    {words, Words} ->
+      collect(N - 1, Parent, Words ++ Acc)
+  end.
 
 % Forms list with 2 edits i.e adding/changing two letters in each word at each position
-edits2(Word) -> lists:usort(lists:foldr(fun(A, AccIn) -> AccIn ++ edits1(A) end, [], edits1(Word))).
+edits2(Word) ->
+  Folded = lists:foldr(fun(A, AccIn) -> [edits1(A) | AccIn] end, [], edits1(Word)),
+  lists:usort(Folded).
 
 
 % Compares all the elements of the words obtained from big.txt and the words formed by edits and returns the possible list of words
-known(Word) ->  
-    FinalDictionary = readfile(?FileName),
-    % Always compare lowercase words
-    LowerWord = string:to_lower(Word),
-    Error1_words = edits1(LowerWord),
-    SuggestedList = words_in_list(FinalDictionary, Error1_words),
-    case lists:member(LowerWord,SuggestedList) of
-        true -> Word;
+known(Word) ->
+  FinalDictionary = readfile(?FileName),
+  % Always compare lowercase words
+  LowerWord = string:to_lower(Word),
+  Error1_words = edits1(LowerWord),
+  SuggestedList = words_in_list(FinalDictionary, Error1_words),
+  case lists:member(LowerWord,SuggestedList) of
+    true -> 
+      Word;
+    false ->
+      case length(SuggestedList) /= 0 of
+        true ->
+          prompt(SuggestedList);
         false ->
-            case length(SuggestedList)=/=0 of
-                true ->
-                    prompt(SuggestedList);
-                false ->
-                    Error2_words = edits2(LowerWord),
-                    SuggestedList2 = words_in_list(FinalDictionary, Error2_words),
-                    case lists:member(LowerWord,SuggestedList2) of
-                      true ->
-                        Word;
-                      false ->
-                        case length(SuggestedList2)=:=0 of
-                          true -> Word;
-                          false -> prompt(SuggestedList2)
-                    end
-                end
-            end
-    end.
+          Error2_words = edits2(LowerWord),
+          SuggestedList2 = words_in_list(FinalDictionary, Error2_words),
+          case lists:member(LowerWord,SuggestedList2) of
+            true ->
+              Word;
+            false ->
+              case length(SuggestedList2)=:=0 of
+                true -> 
+                  Word;
+                false -> 
+                  prompt(SuggestedList2)
+              end
+          end
+      end
+  end.
 
 words_in_list(Words, List) ->
   lists:filter(fun(X) -> lists:member(X,List) end, Words).
@@ -90,11 +136,11 @@ prompt(SuggestedList) ->
 
 % Adds missing words to File "big.txt" only if it is not present in the file
 add(Word) ->
-    WordsInDictionary = readfile(?FileName),
-    case lists:member(Word,WordsInDictionary) of
-      true -> io:format("Word already present~n");
-      false ->  
-              {ok, File} = file:open(?FileName, [append]),
-              file:write(File," " ++ Word),
-              io:format("Thank You!~nWord added to dictionary~n")
-    end.
+  WordsInDictionary = readfile(?FileName),
+  case lists:member(Word,WordsInDictionary) of
+    true -> io:format("Word already present~n");
+    false ->
+      {ok, File} = file:open(?FileName, [append]),
+      file:write(File," " ++ Word),
+      io:format("Thank You!~nWord added to dictionary~n")
+  end.