New filter: index_of, which gives the index of an item in a list.

modules/mod_base/filters/filter_index_of.erl

@@ -0,0 +1,46 @@
+%% @author Arjan Scherpenisse <arjan@scherpenisse.net>
+%% @copyright 2011 Arjan Scherpenisse <arjan@scherpenisse.net>
+%% Date: 2011-09-29
+
+%% @doc Returns the index the given item is in the given list.
+
+%% Copyright 2011 Arjan Scherpenisse
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%% 
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%% 
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+
+-module(filter_index_of).
+-author("Arjan Scherpenisse <arjan@scherpenisse.net>").
+
+-include_lib("include/zotonic.hrl").
+
+-export([index_of/3]).
+
+
+index_of(undefined, _Value, _Context) ->
+    undefined;
+index_of(<<>>, _Value, _Context) -> 
+    undefined;
+index_of(Input, Value, _Context) when is_list(Input) ->
+    ?DEBUG(Input),
+    get_index_of(Value, Input, 1);
+index_of(Input, Value, Context) ->
+    ?DEBUG(Input),
+    index_of(erlydtl_runtime:to_list(Input, Context), Value, Context).
+
+get_index_of(_, [], _)  -> undefined;
+get_index_of(A, [B|Tail], Index) -> 
+    case z_utils:are_equal(A, B) of
+        true -> Index;
+        false ->
+            get_index_of(A, Tail, Index+1)
+    end.