0
@@ -1,24 +1,26 @@
0
 %%% @doc Additional list functions, inspired by Haskell's Data.List.
0
-%%% @author Hasan Veldstra <hasan@12monkeys.co.uk>
0
+%%% @author Hasan Veldstra <hasan@12monkeys.co.uk> [http://12monkeys.co.uk]
0
 %%% Distributed under the same license as Erlang.
0
 
0
 -module(hslists).
0
--import(lists, [all/2, append/1, foreach/2, reverse/1]).
0
+-import(lists, [all/2, append/1, duplicate/2, foldl/3, foreach/2, map/2, reverse/1, seq/2]).
0
 
0
 %% Basic functions.
0
 -export([init/1]).
0
 %% List transformations.
0
--export([intersperse/2, intercalate/2]).
0
+-export([intersperse/2, intercalate/2, transpose/1]).
0
+%% Folds.
0
+-export([product/1]).
0
 
0
+-compile(export_all).
0
 
0
 %% @doc Returns all the elements of a list except the last one.
0
-%% The list must be finite and non-empty.
0
-init(L) when is_list(L) andalso L =/= [] ->
0
+init(L) when is_list(L) ->
0
     reverse(tl(reverse(L))).
0
 
0
 %% @doc Takes an element and a list and 'intersperses' that element between
0
 %% the elements of the list.
0
-intersperse(Elt, L) when is_list(L) ->
0
+intersperse(Elt, L) when is_list(L) andalso L =/= [] ->
0
     tl(intersperse1(Elt, L, [])).
0
 
0
 intersperse1(Elt, [Hd | Tl], Acc) ->
0
@@ -30,3 +32,32 @@ intersperse1(_Elt, [], Acc) ->
0
 %% result.
0
 intercalate(Xs, Xss) ->
0
     append(intersperse(Xs, Xss)).
0
+
0
+%% @doc Transposes the rows and columns of its argument. For example:<br />
0
+%% <code>transpose([[1, 2, 3], [a, b, c]]) = [[1, a], [2, b], [3, c]]</code> <br />
0
+%% All sub-lists must be of the same length.
0
+transpose(L = [Row | _Restrows]) ->
0
+    Len = length(Row),
0
+    lists:foreach(fun(X) ->
0
+                          Len = length(X)
0
+                  end,
0
+                  L),
0
+    Acc = duplicate(Len, []),
0
+    transpose1(L, Acc).
0
+
0
+transpose1([Row | Restrows], Acc) ->
0
+    Newacc = lists:zipwith(fun(X, Y) ->
0
+                                   Y ++ [X]
0
+                           end,
0
+                           Row, Acc),
0
+    transpose1(Restrows, Newacc);
0
+transpose1([], Acc) ->
0
+    Acc.
0
+
0
+%% @doc Computes the product of a list of numbers.
0
+product([Hd | Tl]) ->
0
+    foldl(fun(X, Acc) ->
0
+                  X * Acc
0
+          end,
0
+          Hd,
0
+          Tl).