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=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 08C2F1F463 for ; Mon, 23 Sep 2019 21:16:53 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 7FD881209A1; Tue, 24 Sep 2019 06:16:40 +0900 (JST) Received: from xtrwkhkc.outbound-mail.sendgrid.net (xtrwkhkc.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id B149112092F for ; Tue, 24 Sep 2019 06:16:38 +0900 (JST) Received: by filter0100p3iad2.sendgrid.net with SMTP id filter0100p3iad2-12176-5D893636-3C 2019-09-23 21:16:38.460876756 +0000 UTC m=+3122.970853757 Received: from herokuapp.com (unknown [54.175.75.202]) by ismtpd0060p1mdw1.sendgrid.net (SG) with ESMTP id FKeQTm0qQoWXeUzAIQDe4g for ; Mon, 23 Sep 2019 21:16:38.313 +0000 (UTC) Date: Mon, 23 Sep 2019 21:16:38 +0000 (UTC) From: sammomichael@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 70602 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+KNBmasSPchpKs8OcbQ8x6i5J?= =?us-ascii?Q?R4qBRyEyHuohY6Az3uGXHtM1RVNGxhzwyvKDM3o?= =?us-ascii?Q?n=2FNYW2o0cj1Scjfo=2FCIW+rfp=2F6jyVsXq9Pggu7w?= =?us-ascii?Q?y6rqtArIp2gOrXrzp9KqQ460DoAiu9EontKoHlj?= =?us-ascii?Q?HcsEQKqVChS+YnbGPYyUJ80HEZTGz42GKfQ=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 95047 Subject: [ruby-core:95047] [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). nobu (Nobuyoshi Nakada) wrote: > sammomichael (Samuel Michael) wrote: > > ```ruby > > [for x in 1..10 do x**2 if x.even? end] #=> 1..10 (normal Ruby) > > ``` > > It is an `Array` from 0 to 10 now. Correct thanks I should have wrote [1..10] > > > below we propose a syntax in which we splat the for loop to return the stored result not the caller > > > > ```ruby > > [*for x in 1..10 do x**2 if x.even? end] #=> [4, 16, 36, 64, 100] > > ``` > > Obviously the latter result conflicts with the former. > Which result do you expect from the following code? Hi, I was suggesting a splat operator as one way to create a special syntax, under the hood instead of calling each method it would treat this as a filter map, map, or filter operation, and return the result in place. My intention is to create a flexible alternative syntax to enumerable syntax or using external iteration to do the same thing. Of course it doesn't have to be a splat, just some way to indicate you are invoking the shorthand for Ruby list comprehension, not using Ruby traditional for (.each) loop. Splat could be interpreted here as spreading the values from the block into a new array. > > ```ruby > a = for x in 1..10 do x**2 if x.even? end > [*a] #=> [4, 16, 36, 64, 100] a = 1..10 => [1,2,3,4,5,6,7,8,9,10] for loop results in 1..10 and spreads out to an array the new syntax will not work on ranges only can be declared within [] square brackets at the time of invocation > [*(for x in 1..10 do x**2 if x.even? end)] #=> [1,2,3,4,5,6,7,8,9,10] here the expression in parenthesis would resolve to range 1..10 and be splatted to an array I'm not sure if there is a reason to do this though, but I am open to other opinions if there is something better that should happen > ``` ---------------------------------------- Feature #16147: List Comprehensions in Ruby https://bugs.ruby-lang.org/issues/16147#change-81678 * 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/