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authorHans Bolinder <[email protected]>2018-02-27 15:42:52 +0100
committerHans Bolinder <[email protected]>2018-03-09 14:45:42 +0100
commit5c7209c2874849a5a7339e23fdbd9aed1bb935b2 (patch)
tree66d3f1b29fb11f9db988b514800be926737a5641
parent13e83e2e11b3d211c17c53140249a235b4d7a436 (diff)
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stdlib: Add function lists:search/2
This is essentially PR 102, https://github.com/erlang/otp/pull/102. The OTP Technical Board decided to change the name of the function to search/2.
-rw-r--r--lib/stdlib/doc/src/lists.xml14
-rw-r--r--lib/stdlib/src/lists.erl19
-rw-r--r--lib/stdlib/test/lists_SUITE.erl20
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) ->