From 54ab0c82897759fb29293b9b872f444dc1408dab Mon Sep 17 00:00:00 2001
From: Siraaj Khandkar <siraaj@khandkar.net>
Date: Thu, 30 Jul 2015 00:35:31 -0400
Subject: [PATCH] Add hope_list:map_result/2

---
 src/hope.app.src         |  2 +-
 src/hope_list.erl        | 18 +++++++++++++++++-
 test/hope_list_SUITE.erl | 12 ++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/hope.app.src b/src/hope.app.src
index d2b376c..c5c860f 100644
--- a/src/hope.app.src
+++ b/src/hope.app.src
@@ -1,7 +1,7 @@
 {application, hope,
  [
   {description, "Higher Order Programming in Erlang"},
-  {vsn, "3.6.0"},
+  {vsn, "3.7.0"},
   {registered, []},
   {applications, [
                   kernel,
diff --git a/src/hope_list.erl b/src/hope_list.erl
index f179d1a..63d9c99 100644
--- a/src/hope_list.erl
+++ b/src/hope_list.erl
@@ -10,6 +10,7 @@
     , map/3  % Tunable recursion limit
     , map_rev/2
     , map_slow/2
+    , map_result/2  % Not tail-recursive
     , first_match/2
     ]).
 
@@ -66,7 +67,6 @@ map([X1, X2, X3, X4, X5 | Xs], F, RecursionLimit, RecursionCount) ->
         end,
     [Y1, Y2, Y3, Y4, Y5 | Ys].
 
-
 %% @doc lists:reverse(map_rev(L, F))
 %% @end
 -spec map_slow([A], fun((A) -> (B))) ->
@@ -91,6 +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).
diff --git a/test/hope_list_SUITE.erl b/test/hope_list_SUITE.erl
index 9557aab..7152503 100644
--- a/test/hope_list_SUITE.erl
+++ b/test/hope_list_SUITE.erl
@@ -16,6 +16,7 @@
     , t_map_slow/1
     , t_map/1
     , t_map_3/1
+    , t_map_result/1
     ]).
 
 
@@ -39,6 +40,7 @@ groups() ->
         , t_map_slow
         , t_map
         , t_map_3
+        , t_map_result
         ],
     Properties = [parallel],
     [{?GROUP, Properties, Tests}].
@@ -89,3 +91,13 @@ prop_unique_preserve_order() ->
 
 t_hope_list_specs(_) ->
     [] = proper:check_specs(hope_list).
+
+t_map_result(_Cfg) ->
+    AssertPositive =
+        fun (I) when I > 0 -> {ok, I}; (_) -> {error, negative} end,
+    AllPositives = lists:seq(1, 5),
+    AllNegatives = lists:seq(-5, -1),
+    Mixed = lists:seq(-5, 5),
+    {ok, AllPositives} = hope_list:map_result(AllPositives, AssertPositive),
+    {error, negative}  = hope_list:map_result(AllNegatives, AssertPositive),
+    {error, negative}  = hope_list:map_result(Mixed, AssertPositive).
-- 
2.20.1