From: Siraaj Khandkar Date: Tue, 15 Sep 2015 20:49:27 +0000 (-0400) Subject: Implement (and test) hope_list:divide/2 X-Git-Tag: 3.8.0 X-Git-Url: https://git.xandkar.net/?a=commitdiff_plain;h=cb13c8270d8ff0a333e0a218804843e97bdaa32f;p=hope.git Implement (and test) hope_list:divide/2 Divides list into sublists of up to a requested size + a remainder. Order unspecified. Size < 1 raises an error: hope_list__divide__size_must_be_a_positive_integer. --- diff --git a/src/hope.app.src b/src/hope.app.src index c5c860f..91cd52f 100644 --- a/src/hope.app.src +++ b/src/hope.app.src @@ -1,7 +1,7 @@ {application, hope, [ {description, "Higher Order Programming in Erlang"}, - {vsn, "3.7.0"}, + {vsn, "3.8.0"}, {registered, []}, {applications, [ kernel, diff --git a/src/hope_list.erl b/src/hope_list.erl index 63d9c99..b5edf42 100644 --- a/src/hope_list.erl +++ b/src/hope_list.erl @@ -12,16 +12,14 @@ , map_slow/2 , map_result/2 % Not tail-recursive , first_match/2 + , divide/2 ]). - -define(DEFAULT_RECURSION_LIMIT, 1000). - -type t(A) :: [A]. - %% @doc Tail-recursive equivalent of lists:map/2 %% @end -spec map([A], fun((A) -> (B))) -> @@ -74,7 +72,6 @@ map([X1, X2, X3, X4, X5 | Xs], F, RecursionLimit, RecursionCount) -> map_slow(Xs, F) -> lists:reverse(map_rev(Xs, F)). - %% @doc Tail-recursive alternative to lists:map/2, which accumulates and %% returns list in reverse order. %% @end @@ -129,3 +126,28 @@ first_match([{Tag, F} | Tests], X) -> of true -> {some, Tag} ; false -> first_match(Tests, X) end. + +%% @doc Divide list into sublists of up to a requested size + a remainder. +%% Order unspecified. Size < 1 raises an error: +%% `hope_list__divide__size_must_be_a_positive_integer' +%% @end +-spec divide([A], pos_integer()) -> + [[A]]. +divide(_, Size) when Size < 1 orelse not is_integer(Size) -> + % Q: Why? + % A: For N < 0, what does it mean to have a negative-sized chunk? + % For N = 0, we can imagine that a single chunk is an empty list, but, + % how many such chunks should we produce? + % This is pretty-much equivalnet to the problem of deviding something by 0. + error(hope_list__divide__size_must_be_a_positive_integer); +divide([], _) -> + []; +divide([X1 | Xs], MaxChunkSize) -> + MoveIntoChunks = + fun (X2, {Chunk, Chunks, ChunkSize}) when ChunkSize >= MaxChunkSize -> + {[X2], [Chunk | Chunks], 1} + ; (X2, {Chunk, Chunks, ChunkSize}) -> + {[X2 | Chunk], Chunks, ChunkSize + 1} + end, + {Chunk, Chunks, _} = lists:foldl(MoveIntoChunks, {[X1], [], 1}, Xs), + [Chunk | Chunks]. diff --git a/test/hope_list_SUITE.erl b/test/hope_list_SUITE.erl index e1f8375..386cdc6 100644 --- a/test/hope_list_SUITE.erl +++ b/test/hope_list_SUITE.erl @@ -20,6 +20,7 @@ , t_manual_map_result/1 , t_manual_map_rev/1 , t_manual_map_slow/1 + , t_manual_divide/1 ]). @@ -49,6 +50,7 @@ groups() -> , t_manual_map_result , t_manual_map_rev , t_manual_map_slow + , t_manual_divide ], Properties = [parallel], [{?GROUP, Properties, Tests}]. @@ -84,6 +86,35 @@ t_manual_map_slow(_Cfg) -> [2, 3, 4] = hope_list:map_slow([1, 2, 3], F), [] = hope_list:map_slow([], F). +t_manual_divide(_Cfg) -> + try + hope_list:divide([a, b, c], -1) + catch + error:hope_list__divide__size_must_be_a_positive_integer -> ok + end, + try + hope_list:divide([a, b, c], 0) + catch + error:hope_list__divide__size_must_be_a_positive_integer -> ok + end, + [[c], [b], [a]] = hope_list:divide([a, b, c], 1), + [[c], [b, a]] = hope_list:divide([a, b, c], 2), + [[c, b, a]] = hope_list:divide([a, b, c], 3), + [[c, b, a]] = hope_list:divide([a, b, c], 4), + [[c, b, a]] = hope_list:divide([a, b, c], 5), + try + hope_list:divide([], 0) + catch + error:hope_list__divide__size_must_be_a_positive_integer -> ok + end, + try + hope_list:divide([], -1) + catch + error:hope_list__divide__size_must_be_a_positive_integer -> ok + end, + [[f, e], [d, c], [b, a]] = hope_list:divide([a, b, c, d, e, f], 2), + [[f, e, d], [c, b, a]] = hope_list:divide([a, b, c, d, e, f], 3). + %% ============================================================================= %% Generated test cases %% =============================================================================