File 3203-Add-a-filtermap-function-to-the-queue-module.patch of Package erlang
From 496e490de24cece137b9adb543c390f9e7703e45 Mon Sep 17 00:00:00 2001
From: Maria-12648430 <maria-12648430@gmx.net>
Date: Mon, 26 Oct 2020 09:53:04 +0100
Subject: [PATCH 3/3] Add a filtermap function to the queue module
---
lib/stdlib/doc/src/queue.xml | 16 ++++++++++++++
lib/stdlib/src/queue.erl | 38 ++++++++++++++++++++++++++++++++-
lib/stdlib/test/queue_SUITE.erl | 8 +++++++
3 files changed, 61 insertions(+), 1 deletion(-)
diff --git a/lib/stdlib/doc/src/queue.xml b/lib/stdlib/doc/src/queue.xml
index cd92547268..98971b1f4e 100644
--- a/lib/stdlib/doc/src/queue.xml
+++ b/lib/stdlib/doc/src/queue.xml
@@ -54,6 +54,7 @@
<p>All operations have an amortized O(1) running time, except
<seealso marker="#filter/2"><c>filter/2</c></seealso>,
+ <seealso marker="#filtermap/2"><c>filtermap/2</c></seealso>,
<seealso marker="#fold/3"><c>fold/3</c></seealso>,
<seealso marker="#join/2"><c>join/2</c></seealso>,
<seealso marker="#len/1"><c>len/1</c></seealso>,
@@ -135,6 +136,21 @@
</desc>
</func>
+ <func>
+ <name name="filtermap" arity="2"/>
+ <fsummary>Filter and map a queue.</fsummary>
+ <desc>
+ <p>Returns a queue <c><anno>Q2</anno></c> that is the result of calling
+ <c><anno>Fun</anno>(<anno>Item</anno>)</c> on all items in
+ <c><anno>Q1</anno></c>, in order from front to rear.</p>
+ <p>If <c><anno>Fun</anno>(<anno>Item</anno>)</c> returns <c>true</c>,
+ <c>Item</c> is copied to the result queue. If it returns <c>false</c>,
+ <c><anno>Item</anno></c> is not copied. If it returns
+ <c>{true, NewItem}</c>, the queue element at this position is replaced
+ with <c>NewItem</c> in the result queue.</p>
+ </desc>
+ </func>
+
<func>
<name name="fold" arity="3"/>
<fsummary>Fold a function over a queue.</fsummary>
diff --git a/lib/stdlib/src/queue.erl b/lib/stdlib/src/queue.erl
index 9a132f0330..06c8ae51df 100644
--- a/lib/stdlib/src/queue.erl
+++ b/lib/stdlib/src/queue.erl
@@ -27,7 +27,7 @@
-export([get/1,get_r/1,peek/1,peek_r/1,drop/1,drop_r/1]).
%% Higher level API
--export([reverse/1,join/2,split/2,filter/2,fold/3]).
+-export([reverse/1,join/2,split/2,filter/2,filtermap/2,fold/3]).
%% Okasaki API from klacke
-export([cons/2,head/1,tail/1,
@@ -402,6 +402,42 @@ filter_r(Fun, [X|R0]) ->
lists:reverse(L, R)
end.
+%% Filter and map a queue, traverses in queue order.
+%%
+%% O(len(Q1))
+-spec filtermap(Fun, Q1) -> Q2 when
+ Fun :: fun((Item) -> boolean() | {'true', Value}),
+ Q1 :: queue(Item),
+ Q2 :: queue(Item | Value),
+ Item :: term(),
+ Value :: term().
+filtermap(Fun, {R0, F0}) when is_function(Fun, 1), is_list(R0), is_list(F0) ->
+ F = lists:filtermap(Fun, F0),
+ R = filtermap_r(Fun, R0),
+ if R =:= [] ->
+ f2r(F);
+ F =:= [] ->
+ r2f(R);
+ true ->
+ {R,F}
+ end;
+filtermap(Fun, Q) ->
+ erlang:error(badarg, [Fun,Q]).
+
+%% Call Fun in reverse order, i.e tail to head
+filtermap_r(_, []) ->
+ [];
+filtermap_r(Fun, [X|R0]) ->
+ R = filtermap_r(Fun, R0),
+ case Fun(X) of
+ true ->
+ [X|R];
+ {true, Y} ->
+ [Y|R];
+ false ->
+ R
+ end.
+
%% Fold a function over a queue, in queue order.
%%
%% O(len(Q))
diff --git a/lib/stdlib/test/queue_SUITE.erl b/lib/stdlib/test/queue_SUITE.erl
index c85dd14278..f2bad3c3b8 100644
--- a/lib/stdlib/test/queue_SUITE.erl
+++ b/lib/stdlib/test/queue_SUITE.erl
@@ -373,6 +373,14 @@ do_op_test(F) ->
(_) -> [] end, MyQ4)),
[33,44] = queue:to_list(queue:filter(fun(X) when X < 27 -> false;
(X) -> [X] end, MyQ4)),
+ [11,22*22,33*33] = queue:to_list(queue:filtermap(fun(X) when X < 17 -> true;
+ (X) when X > 37 -> false;
+ (X) -> {true, X*X}
+ end, MyQ4)),
+ [22*22,33*33,44] = queue:to_list(queue:filtermap(fun(X) when X < 17 -> false;
+ (X) when X > 37 -> true;
+ (X) -> {true, X*X}
+ end, MyQ4)),
FoldQ = queue:from_list(L1),
FoldExp1 = lists:sum(L1),
FoldAct1 = queue:fold(fun(X,A) -> X+A end, 0, FoldQ),
--
2.26.2
