From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS4713 221.184.0.0/13 X-Spam-Status: No, score=-2.8 required=3.0 tests=AWL,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS shortcircuit=no autolearn=no autolearn_force=no version=3.4.2 Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by dcvr.yhbt.net (Postfix) with ESMTP id C4FC91F461 for ; Fri, 6 Sep 2019 16:44:19 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 2D048120A6F; Sat, 7 Sep 2019 01:44:12 +0900 (JST) Received: from o1678916x28.outbound-mail.sendgrid.net (o1678916x28.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id 34194120A6F for ; Sat, 7 Sep 2019 01:44:10 +0900 (JST) Received: by filter0139p3mdw1.sendgrid.net with SMTP id filter0139p3mdw1-22241-5D728CD9-10 2019-09-06 16:44:09.256634765 +0000 UTC m=+258553.836221735 Received: from herokuapp.com (unknown [100.24.30.249]) by ismtpd0010p1iad1.sendgrid.net (SG) with ESMTP id LEAe6MOjS0uXbT4AHswkkg for ; Fri, 06 Sep 2019 16:44:09.215 +0000 (UTC) Date: Fri, 06 Sep 2019 16:44:09 +0000 (UTC) From: sammomichael@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 70360 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 16147 X-Redmine-Issue-Author: sammomichael X-Redmine-Sender: sammomichael X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-SG-EID: =?us-ascii?Q?slqsTT=2F+PuUcADLY9nggyMdJj+djGZd32YYUR+KNBmblbvMu9NJOSaFrqrrMke?= =?us-ascii?Q?2GCChxBrkS4B1ovJM2YgHjcHlYOsjvvbLa7RDSv?= =?us-ascii?Q?=2F6+Lec2cMuC7f7irc28ONNgdMYOcRiDGj409Y9B?= =?us-ascii?Q?zKRYqbBPcxNdqzg2krGuq7cB9+uAg8MCNdTnLY3?= =?us-ascii?Q?kAc6JPxRrCAVD+a1pjaHgHQs=2F5Klq4v30MQ=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 94805 Subject: [ruby-core:94805] [Ruby master Feature#16147] List Comprehensions in Ruby X-BeenThere: ruby-core@ruby-lang.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Ruby developers List-Id: Ruby developers List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #16147 has been updated by sammomichael (Samuel Michael). There is nothing wrong with the current ruby syntax of using enumerables such as map/select/filter_map to generate the same type of list. But as you said ruby is all about many ways of doing things. And as many languages offer some version of this feature (Julia, Python, CoffeeScript, etc.) it could be beneficial for ruby to incorporate its own variation. There is something natural and refreshing about using pure mathematical set builder notation with keywords for...in to generate an array. `[*1..10].filter_map{@1**2 if @1.even?}` vs `[x**2 for x in 1..10 if x.even?]` The second version has less symbols, less keystrokes and is more human readable for beginners imo. Also I didn't mean to suggest that we retire the normal for...in loop (which I use myself) to break older code or that nobody ever uses it, but I am suggesting that we extend it if possible, just as was done with making "in" the keyword for the new pattern matching system. ---------------------------------------- Feature #16147: List Comprehensions in Ruby https://bugs.ruby-lang.org/issues/16147#change-81427 * Author: sammomichael (Samuel Michael) * Status: Open * Priority: Normal * Assignee: * Target version: ---------------------------------------- ## List comprehensions are present in many languages and programmers are quite fond of their simplicity and power. Add to that the fact that Ruby has a for...in loop that is rarely used but could possibly be repurposed. ### Currently we can already do a hack like this to make Ruby support list comprehension syntax: ``` ruby S = [for x in 0...9 do $* << x*2 if x.even? end, $*][1] # [0, 4, 8, 12, 16] ``` Still, it would be far nicer if the for...in loop would return the desired array automatically, this is one way to approach that taking advantage of lambda bracket invocation syntax: ``` ruby c = -> x do $*.clear if x['if'] && x[0] != 'f' . y = x[0...x.index('for')] x = x[x.index('for')..-1] (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << #{y}") x.insert(x.length, "end; $*") eval(x) $*) elsif x['if'] && x[0] == 'f' (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << x") x.insert(x.length, "end; $*") eval(x) $*) elsif !x['if'] && x[0] != 'f' y = x[0...x.index('for')] x = x[x.index('for')..-1] (x.insert(x.index(x.split[3]) + x.split[3].length, " do $* << #{y}") x.insert(x.length, "end; $*") eval(x) $*) else eval(x.split[3]).to_a end end ``` so basically we are converting a string to proper ruby syntax for loop then we can use python syntax in a string to do: ``` ruby c['for x in 1..10'] c['for x in 1..10 if x.even?'] c['x**2 for x in 1..10 if x.even?'] c['x**2 for x in 1..10'] # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] # [2, 4, 6, 8, 10] # [4, 16, 36, 64, 100] # [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] ``` -- https://bugs.ruby-lang.org/