wolever · December 25, 2009 04:48 · Dec 26, 2009 · Dec 25, 2009
diff --git a/trie.erl b/trie.erl
@@ -44,3 +44,15 @@ at_word(Trie) ->
         { ok, _ } -> true;
         error -> false
     end.
+
+%
+% Example usage
+%
+word_in_trie([], Trie) -> at_word(Trie);
+word_in_trie([Ch|Rest], Trie) ->
+   case trie:step(Ch, Trie) of
+       { ok, NextTrie } ->
+           word_in_trie(Rest, NextTrie);
+       error ->
+           false
+   end.
diff --git a/trie.erl b/trie.erl
@@ -0,0 +1,46 @@
+-module(trie).
+-export([new/0, add/2, step/2, from_dict/0, at_word/1]).
+
+setdefault(Key, Default, Dict) ->
+    case dict:find(Key, Dict) of
+        { ok, Value } ->
+            { Dict, Value };
+        error ->
+            { dict:store(Key, Default, Dict), Default }
+    end.
+
+new() ->
+    dict:new().
+
+add([], Trie) ->
+    dict:store(stop, true, Trie);
+
+add([Ch|Rest], Trie) ->
+    { NewTrie, SubTrie } = setdefault(Ch, dict:new(), Trie),
+    NewSubTrie = add(Rest, SubTrie),
+    dict:store(Ch, NewSubTrie, NewTrie).
+
+step(Ch, Trie) ->
+    dict:find(Ch, Trie).
+
+from_dict() ->
+    { ok, File } = file:open("/usr/share/dict/words", [read]),
+    %{ ok, File } = file:open("/tmp/x", [read]),
+    from_dict(new(), File).
+
+from_dict(CurTrie, File) ->
+    case io:get_line(File, "") of
+        eof ->
+            file:close(File),
+            CurTrie;
+        UnfixedLine ->
+            Line = string:strip(string:to_lower(UnfixedLine), both, $\n),
+            NewTrie = add(Line, CurTrie),
+            from_dict(NewTrie, File)
+    end.
+
+at_word(Trie) ->
+    case dict:find(stop, Trie) of
+        { ok, _ } -> true;
+        error -> false
+    end.