File 2175-Implement-lists-join-2.patch of Package erlang
From c660e30a7dd781f71bed050b20c3e2d0b069e063 Mon Sep 17 00:00:00 2001
From: Jesper Louis Andersen <jesper.louis.andersen@gmail.com>
Date: Sat, 9 Apr 2016 17:17:59 +0200
Subject: [PATCH] Implement lists:join/2
Add a call which works much like string:join/2 but for arbitrary lists. Provide
the function itself, lifted from Haskells Data.List standard library, provide
documentation and provide tests for the function.
---
lib/stdlib/doc/src/lists.xml | 15 +++++++++++++++
lib/stdlib/src/lists.erl | 15 ++++++++++++++-
lib/stdlib/test/lists_SUITE.erl | 16 +++++++++++++++-
3 files changed, 44 insertions(+), 2 deletions(-)
diff --git a/lib/stdlib/doc/src/lists.xml b/lib/stdlib/doc/src/lists.xml
index 89ba523..84e9615 100644
--- a/lib/stdlib/doc/src/lists.xml
+++ b/lib/stdlib/doc/src/lists.xml
@@ -262,6 +262,21 @@ flatmap(Fun, List1) ->
</desc>
</func>
<func>
+ <name name="join" arity="2"/>
+ <fsummary>Insert an element between elements in a list</fsummary>
+ <desc>
+ <p>Inserts <c><anno>Sep</anno></c> between each element in <c><anno>List1</anno></c>. Has no
+ effect on the empty list and on a singleton list. For example:</p>
+ <pre>
+> <input>lists:join(x, [a,b,c]).</input>
+[a,x,b,x,c]
+> <input>lists:join(x, [a]).</input>
+[a]
+> <input>lists:join(x, []).</input>
+[]</pre>
+ </desc>
+ </func>
+ <func>
<name name="foreach" arity="2"/>
<fsummary>Apply a function to each element of a list</fsummary>
<desc>
diff --git a/lib/stdlib/src/lists.erl b/lib/stdlib/src/lists.erl
index 2b4472c..af9d63d 100644
--- a/lib/stdlib/src/lists.erl
+++ b/lib/stdlib/src/lists.erl
@@ -39,7 +39,8 @@
-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]).
+ split/2,
+ join/2]).
%%% BIFs
-export([keyfind/3, keymember/3, keysearch/3, member/2, reverse/2]).
@@ -1439,6 +1440,18 @@ split(N, [H|T], R) ->
split(_, [], _) ->
badarg.
+-spec join(Sep, List1) -> List2 when
+ Sep :: T,
+ List1 :: [T],
+ List2 :: [T],
+ T :: term().
+
+join(_Sep, []) -> [];
+join(Sep, [H|T]) -> [H|join_prepend(Sep, T)].
+
+join_prepend(_Sep, []) -> [];
+join_prepend(Sep, [H|T]) -> [Sep,H|join_prepend(Sep,T)].
+
%%% =================================================================
%%% Here follows the implementation of the sort functions.
%%%
diff --git a/lib/stdlib/test/lists_SUITE.erl b/lib/stdlib/test/lists_SUITE.erl
index b21eb37..f3711c5 100644
--- a/lib/stdlib/test/lists_SUITE.erl
+++ b/lib/stdlib/test/lists_SUITE.erl
@@ -55,6 +55,7 @@
ufunsort_error/1,
zip_unzip/1, zip_unzip3/1, zipwith/1, zipwith3/1,
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]).
@@ -119,7 +120,7 @@ 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, join,
hof]}
].
@@ -2413,6 +2414,19 @@ zipwith3(Config) when is_list(Config) ->
ok.
+%% Test lists:join/2
+join(Config) when is_list(Config) ->
+ A = [a,b,c],
+ Sep = x,
+ [a,x,b,x,c] = lists:join(Sep, A),
+
+ B = [b],
+ [b] = lists:join(Sep, B),
+
+ C = [],
+ [] = lists:join(Sep, C),
+ ok.
+
%% Test lists:filter/2, lists:partition/2.
filter_partition(Config) when is_list(Config) ->
F = fun(I) -> I rem 2 =:= 0 end,
--
2.1.4
