diff options
| -rw-r--r-- | lib/stdlib/doc/src/lists.xml | 14 | ||||
| -rw-r--r-- | lib/stdlib/src/lists.erl | 19 | ||||
| -rw-r--r-- | lib/stdlib/test/lists_SUITE.erl | 20 |
3 files changed, 46 insertions, 7 deletions
diff --git a/lib/stdlib/doc/src/lists.xml b/lib/stdlib/doc/src/lists.xml index 7efafedc82..c3d5d7e07a 100644 --- a/lib/stdlib/doc/src/lists.xml +++ b/lib/stdlib/doc/src/lists.xml @@ -4,7 +4,7 @@ <erlref> <header> <copyright> - <year>1996</year><year>2017</year> + <year>1996</year><year>2018</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -771,6 +771,18 @@ length(lists:seq(From, To, Incr)) =:= (To - From + Incr) div Incr</code> </func> <func> + <name name="search" arity="2"/> + <fsummary>Find the first element that satisfies a predicate.</fsummary> + <desc> + <p>If there is a <c><anno>Value</anno></c> in <c><anno>List</anno></c> + such that <c><anno>Pred</anno>(<anno>Value</anno>)</c> returns + <c>true</c>, returns <c>{value, <anno>Value</anno>}</c> + for the first such <c><anno>Value</anno></c>, + otherwise returns <c>false</c>.</p> + </desc> + </func> + + <func> <name name="splitwith" arity="2"/> <fsummary>Split a list into two lists based on a predicate.</fsummary> <desc> diff --git a/lib/stdlib/src/lists.erl b/lib/stdlib/src/lists.erl index af9d63ddd6..06c90c0280 100644 --- a/lib/stdlib/src/lists.erl +++ b/lib/stdlib/src/lists.erl @@ -1,7 +1,7 @@ %% %% %CopyrightBegin% %% -%% Copyright Ericsson AB 1996-2016. All Rights Reserved. +%% Copyright Ericsson AB 1996-2018. All Rights Reserved. %% %% Licensed under the Apache License, Version 2.0 (the "License"); %% you may not use this file except in compliance with the License. @@ -38,8 +38,8 @@ -export([all/2,any/2,map/2,flatmap/2,foldl/3,foldr/3,filter/2, partition/2,zf/2,filtermap/2, - mapfoldl/3,mapfoldr/3,foreach/2,takewhile/2,dropwhile/2,splitwith/2, - split/2, + mapfoldl/3,mapfoldr/3,foreach/2,takewhile/2,dropwhile/2, + search/2, splitwith/2,split/2, join/2]). %%% BIFs @@ -1399,6 +1399,19 @@ dropwhile(Pred, [Hd|Tail]=Rest) -> end; dropwhile(Pred, []) when is_function(Pred, 1) -> []. +-spec search(Pred, List) -> {value, Value} | false when + Pred :: fun((T) -> boolean()), + List :: [T], + Value :: T. + +search(Pred, [Hd|Tail]) -> + case Pred(Hd) of + true -> {value, Hd}; + false -> search(Pred, Tail) + end; +search(Pred, []) when is_function(Pred, 1) -> + false. + -spec splitwith(Pred, List) -> {List1, List2} when Pred :: fun((T) -> boolean()), List :: [T], diff --git a/lib/stdlib/test/lists_SUITE.erl b/lib/stdlib/test/lists_SUITE.erl index 7c99244b36..837ab4e97e 100644 --- a/lib/stdlib/test/lists_SUITE.erl +++ b/lib/stdlib/test/lists_SUITE.erl @@ -1,7 +1,7 @@ %% %% %CopyrightBegin% %% -%% Copyright Ericsson AB 1997-2017. All Rights Reserved. +%% Copyright Ericsson AB 1997-2018. All Rights Reserved. %% %% Licensed under the Apache License, Version 2.0 (the "License"); %% you may not use this file except in compliance with the License. @@ -57,7 +57,7 @@ filter_partition/1, join/1, otp_5939/1, otp_6023/1, otp_6606/1, otp_7230/1, - suffix/1, subtract/1, droplast/1, hof/1]). + suffix/1, subtract/1, droplast/1, search/1, hof/1]). %% Sort randomized lists until stopped. %% @@ -121,7 +121,7 @@ groups() -> {zip, [parallel], [zip_unzip, zip_unzip3, zipwith, zipwith3]}, {misc, [parallel], [reverse, member, dropwhile, takewhile, filter_partition, suffix, subtract, join, - hof, droplast]} + hof, droplast, search]} ]. init_per_suite(Config) -> @@ -2615,6 +2615,20 @@ droplast(Config) when is_list(Config) -> ok. +%% Test lists:search/2 +search(Config) when is_list(Config) -> + F = fun(I) -> I rem 2 =:= 0 end, + F2 = fun(A, B) -> A > B end, + + {value, 2} = lists:search(F, [1,2,3,4]), + false = lists:search(F, [1,3,5,7]), + false = lists:search(F, []), + + %% Error cases. + {'EXIT',{function_clause,_}} = (catch lists:search(badfun, [])), + {'EXIT',{function_clause,_}} = (catch lists:search(F2, [])), + ok. + %% Briefly test the common high-order functions to ensure they %% are covered. hof(Config) when is_list(Config) -> |