Add hope_list:map_result/2

[hope.git] / src / hope_list.erl

diff --git a/src/hope_list.erl b/src/hope_list.erl
index aba9944..63d9c99 100644 (file)
--- a/src/hope_list.erl
+++ b/src/hope_list.erl
@@ -6,15 +6,67 @@
 
 -export(
     [ unique_preserve_order/1
+    , map/2
+    , map/3  % Tunable recursion limit
     , map_rev/2
     , map_slow/2
+    , map_result/2  % Not tail-recursive
+    , first_match/2
     ]).
 
 
+-define(DEFAULT_RECURSION_LIMIT, 1000).
+
+
 -type t(A) ::
     [A].
 
 
+%% @doc Tail-recursive equivalent of lists:map/2
+%% @end
+-spec map([A], fun((A) -> (B))) ->
+    [B].
+map(Xs, F) ->
+    map(Xs, F, ?DEFAULT_RECURSION_LIMIT).
+
+-spec map([A], fun((A) -> (B)), RecursionLimit :: non_neg_integer()) ->
+    [B].
+map(Xs, F, RecursionLimit) ->
+    map(Xs, F, RecursionLimit, 0).
+
+map([], _, _, _) ->
+    [];
+map([X1], F, _, _) ->
+    Y1 = F(X1),
+    [Y1];
+map([X1, X2], F, _, _) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    [Y1, Y2];
+map([X1, X2, X3], F, _, _) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    Y3 = F(X3),
+    [Y1, Y2, Y3];
+map([X1, X2, X3, X4], F, _, _) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    Y3 = F(X3),
+    Y4 = F(X4),
+    [Y1, Y2, Y3, Y4];
+map([X1, X2, X3, X4, X5 | Xs], F, RecursionLimit, RecursionCount) ->
+    Y1 = F(X1),
+    Y2 = F(X2),
+    Y3 = F(X3),
+    Y4 = F(X4),
+    Y5 = F(X5),
+    Ys =
+        case RecursionCount > RecursionLimit
+        of  true  -> map_slow(Xs, F)
+        ;   false -> map     (Xs, F, RecursionLimit, RecursionCount + 1)
+        end,
+    [Y1, Y2, Y3, Y4, Y5 | Ys].
+
 %% @doc lists:reverse(map_rev(L, F))
 %% @end
 -spec map_slow([A], fun((A) -> (B))) ->
@@ -23,7 +75,8 @@ map_slow(Xs, F) ->
     lists:reverse(map_rev(Xs, F)).
 
 
-%% @doc O(N), tail-recursive equivalent to lists:rev(lists:map(F, L))
+%% @doc Tail-recursive alternative to lists:map/2, which accumulates and
+%% returns list in reverse order.
 %% @end
 -spec map_rev([A], fun((A) -> (B))) ->
     [B].
@@ -38,6 +91,22 @@ map_rev_acc([X|Xs], F, Ys) ->
     Y = F(X),
     map_rev_acc(Xs, F, [Y|Ys]).
 
+-spec map_result([A], fun((A) -> (hope_result:t(B, C)))) ->
+    hope_result:t([B], C).
+map_result([], _) ->
+    {ok, []};
+map_result([X | Xs], F) ->
+    case F(X)
+    of  {ok, Y} ->
+            case map_result(Xs, F)
+            of  {ok, Ys} ->
+                    {ok, [Y | Ys]}
+            ;   {error, _}=Error ->
+                    Error
+            end
+    ;   {error, _}=Error ->
+            Error
+    end.
 
 -spec unique_preserve_order(t(A)) ->
     t(A).
@@ -50,3 +119,13 @@ unique_preserve_order(L) ->
             end
         end,
     lists:reverse(lists:foldl(PrependIfNew, [], L)).
+
+-spec first_match([{Tag, fun((A) -> boolean())}], A) ->
+    hope_option:t(Tag).
+first_match([], _) ->
+    none;
+first_match([{Tag, F} | Tests], X) ->
+    case F(X)
+    of  true  -> {some, Tag}
+    ;   false -> first_match(Tests, X)
+    end.