diff options
| -rw-r--r-- | lib/stdlib/doc/src/lists.xml | 15 | ||||
| -rw-r--r-- | lib/stdlib/src/lists.erl | 15 | ||||
| -rw-r--r-- | 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 89ba5238b5..84e9615e4f 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 2b4472cdf7..af9d63ddd6 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 b21eb37ee3..f3711c569e 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, |