From: daniel@dan42.com
To: ruby-core@ruby-lang.org
Subject: [ruby-core:94799] [Ruby master Bug#16147] List Comprehensions in Ruby
Date: Fri, 06 Sep 2019 13:18:50 +0000 (UTC) [thread overview]
Message-ID: <redmine.journal-81420.20190906131850.2b4126ddac05c58e@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-16147.20190906103822@ruby-lang.org
Issue #16147 has been updated by Dan0042 (Daniel DeLorme).
What's wrong with existing well-established ruby idioms?
```ruby
(1..0).to_a
(1..0).select(&:even?)
(1..0).select(&:even?).map{ |x| x**2 }
(1..0).map{ |x| x**2 }
```
or in ruby 2.7:
```ruby
(1..0).to_a
(1..0).select(&:even?)
(1..0).select(&:even?).map{ _0**2 }
(1..0).map{ _0**2 }
```
or if #16120 was accepted ;-D
```ruby
(1..0).to_a
(1..0).select{.even?}
(1..0).select{.even?}.map{.**2}
(1..0).map{.**2}
```
----------------------------------------
Bug #16147: List Comprehensions in Ruby
https://bugs.ruby-lang.org/issues/16147#change-81420
* Author: sammomichael (Samuel Michael)
* Status: Open
* Priority: Normal
* Assignee:
* Target version:
* ruby -v:
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
## 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/
next prev parent reply other threads:[~2019-09-06 13:18 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-16147.20190906103822@ruby-lang.org>
2019-09-06 10:38 ` [ruby-core:94796] [Ruby master Bug#16147] List Comprehensions in Ruby sammomichael
2019-09-06 13:18 ` daniel [this message]
2019-09-06 14:06 ` [ruby-core:94800] " shevegen
2019-09-06 16:41 ` [ruby-core:94804] [Ruby master Feature#16147] " sammomichael
2019-09-06 16:44 ` [ruby-core:94805] " sammomichael
2019-09-06 17:28 ` [ruby-core:94807] " sammomichael
2019-09-21 21:46 ` [ruby-core:95026] " sammomichael
2019-09-22 10:09 ` [ruby-core:95031] " nobu
2019-09-22 16:47 ` [ruby-core:95035] " eregontp
2019-09-23 21:16 ` [ruby-core:95047] " sammomichael
2019-09-23 22:06 ` [ruby-core:95049] " sammomichael
2019-09-29 2:26 ` [ruby-core:95144] " sammomichael
2019-10-03 17:57 ` [ruby-core:95200] " sammomichael
2019-10-04 0:41 ` [ruby-core:95213] " sammomichael
2019-10-07 13:01 ` [ruby-core:95259] " sammomichael
2019-10-07 18:35 ` [ruby-core:95262] " sammomichael
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