From 2ae8ec4507c090d51df41e21f7ad7786de040aad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 8 Sep 2015 10:25:55 +0200
Subject: lists_SUITE: Add hof/1 to test all high-order functions

---
 lib/stdlib/test/lists_SUITE.erl | 42 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/lib/stdlib/test/lists_SUITE.erl b/lib/stdlib/test/lists_SUITE.erl
index 6bed793028..a0f7fd2744 100644
--- a/lib/stdlib/test/lists_SUITE.erl
+++ b/lib/stdlib/test/lists_SUITE.erl
@@ -62,7 +62,7 @@
 	 zip_unzip/1, zip_unzip3/1, zipwith/1, zipwith3/1,
 	 filter_partition/1, 
 	 otp_5939/1, otp_6023/1, otp_6606/1, otp_7230/1,
-	 suffix/1, subtract/1, droplast/1]).
+	 suffix/1, subtract/1, droplast/1, hof/1]).
 
 %% Sort randomized lists until stopped.
 %%
@@ -123,7 +123,8 @@ groups() ->
      {tickets, [parallel], [otp_5939, otp_6023, otp_6606, otp_7230]},
      {zip, [parallel], [zip_unzip, zip_unzip3, zipwith, zipwith3]},
      {misc, [parallel], [reverse, member, dropwhile, takewhile,
-			 filter_partition, suffix, subtract]}
+			 filter_partition, suffix, subtract,
+			 hof]}
     ].
 
 init_per_suite(Config) ->
@@ -2708,3 +2709,40 @@ droplast(Config) when is_list(Config) ->
     ?line {'EXIT', {function_clause, _}} = (catch lists:droplast(x)),
 
     ok.
+
+%% Briefly test the common high-order functions to ensure they
+%% are covered.
+hof(Config) when is_list(Config) ->
+    L = [1,2,3],
+    [1,4,9] = lists:map(fun(N) -> N*N end, L),
+    [1,4,5,6] = lists:flatmap(fun(1) -> [1];
+				 (2) -> [];
+				 (3) -> [4,5,6]
+			      end, L),
+    [{1,[a]},{2,[b]},{3,[c]}] =
+	lists:keymap(fun(A) -> [A] end, 2, [{1,a},{2,b},{3,c}]),
+
+    [1,3] = lists:filter(fun(N) -> N rem 2 =:= 1 end, L),
+    FilterMapFun = fun(1) -> true;
+		      (2) -> {true,42};
+		      (3) -> false
+		   end,
+    [1,42] = lists:filtermap(FilterMapFun, L),
+    [1,42] = lists:zf(FilterMapFun, L),
+
+    [3,2,1] = lists:foldl(fun(E, A) -> [E|A] end, [], L),
+    [1,2,3] = lists:foldr(fun(E, A) -> [E|A] end, [], L),
+    {[1,4,9],[3,2,1]} = lists:mapfoldl(fun(E, A) ->
+					       {E*E,[E|A]}
+				       end, [], L),
+    {[1,4,9],[1,2,3]} = lists:mapfoldr(fun(E, A) ->
+					       {E*E,[E|A]}
+				       end, [], L),
+
+    true = lists:any(fun(N) -> N =:= 2 end, L),
+    false = lists:any(fun(N) -> N =:= 42 end, L),
+
+    true = lists:all(fun(N) -> is_integer(N) end, L),
+    false = lists:all(fun(N) -> N rem 2 =:= 0 end, L),
+
+    ok.
-- 
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