{"id":491,"date":"2010-05-31T15:50:42","date_gmt":"2010-05-31T14:50:42","guid":{"rendered":"http:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/"},"modified":"2010-05-31T15:50:42","modified_gmt":"2010-05-31T14:50:42","slug":"a-working-bogosort-in-perl6","status":"publish","type":"post","link":"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/","title":{"rendered":"A working bogosort in Perl6"},"content":{"rendered":"

It's not even mine actually. @moritz helped me with that. I couldn't remember the syntax for the reduce operator (and it's [<op>]<\/code>), so here it is, in its full wikipedia glory<\/a>.<\/p>\n

\r\n@list .= pick(*) until [<=] @list\r\n<\/pre>\n
Here's a somewhat more complete example, that you can actually run:<\/p>\n
\r\nmy @list = 1, 2, 7, 4, 3;\r\n@list .= pick(*) until [<=] @list;\r\nsay @list.perl;\r\n<\/pre>\n
This will bogosort the array (wikipedia)<\/a>, that is, shuffle it until it's ordered. Look at the Java version for a nice comparison.<\/p>\n
Here's the explanation:<\/p>\n
\r\nmy @list = 1, 2, 7, 4, 3;\r\n<\/pre>\n
Declares the list. You don't need parens around the elements. If that was a deck of cards, you could write it as:<\/p>\n
\r\nmy @list = <A 2 3 4 5 6 7 8 9 J Q K>\r\n<\/pre>\n
The angular brackets <><\/code> are the equivalent of qw()<\/code> in Perl 5. Following line is quite dense:<\/p>\n
\r\n@list .= pick(*) until [<=] @list;\r\n<\/pre>\n
This can be written also as:<\/p>\n
\r\nwhile not [<=] @list {\r\n  @list .= pick(*)\r\n}\r\n<\/pre>\n
As you can see, you don't need parens around the while<\/code> condition. The [<=] @list<\/code> bit is IINM a reduce operator for a list. For example, to sum all elements of a list, you'd use:<\/p>\n
\r\nmy @num = 1, 2, 3, 4;\r\nsay [+] @num;\r\n<\/pre>\n
So the [<=]<\/code> operator applied to a list compares each element with the next one, then the result with the next one. Assuming @list = 2, 4, 8, 5<\/code>, that is how I think it runs:<\/p>\n
\r\n2 <= 4 (true, go on, last evaluated value is 4)\r\n4 <= 8 (true, go on, last value is 8)\r\n8 <= 5 (false, stop here, return value is false)\r\n<\/pre>\n
So, if the array is ordered, the while\/until block is skipped. If the array is not ordered, execute the following:<\/p>\n
\r\n@list .= pick(*)\r\n<\/pre>\n
.=<\/code> is an operator for in-place method call<\/b>. Writing that is equivalent to:<\/p>\n
\r\n@list = @list.pick(*)\r\n<\/pre>\n
That in Perl 5 would be written as:<\/p>\n
\r\n$list = SomeListObject->new(1, 2, 3, 4, 5);\r\n$list->pick(???);\r\n<\/pre>\n
Actually, there wouldn't be any Perl 5 direct equivalent code, since the magic bit here (the *, aka "whatever")<\/b> it's not even there. "whatever" is magic for "anything that's applicable here, until there's an end to it"<\/i>, or at least this is my ignorant interpretation of it… :)<\/p>\n
So in this context, pick()<\/code> is a method that returns a random element from a list. Together with *<\/code>, it means pick a random element from any of the original @list<\/code>. Mmmh. But then it should be equivalent to:<\/p>\n
\r\n@list .= pick(@list)\r\n<\/pre>\n
But it's not, so pick(*)<\/code> knows<\/b> the right thing to do…
\nAnd it's clear that I don't know how pick() works :)
Anyway…<\/p>\n
BTW, this is runnable code<\/b>. If you want to try it, clone the rakudo<\/a> repository, and run perl Configure.pl --gen-parrot<\/code> to build it. Have fun!<\/p><\/p>\n","protected":false},"excerpt":{"rendered":"
It's not even mine actually. @moritz helped me with that. I couldn't remember the syntax for the reduce operator (and it's [<op>]), so here it is, in its full wikipedia glory. @list .= pick(*) until [<=] @list Here's a somewhat more complete example, that you can actually run: my @list = 1, 2, 7, 4, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[431,430,50,290,286,429,428],"yoast_head":"\nA working bogosort in Perl6 - Random hacking<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"A working bogosort in Perl6 - Random hacking\" \/>\n<meta property=\"og:description\" content=\"It's not even mine actually. @moritz helped me with that. I couldn't remember the syntax for the reduce operator (and it's [<op>]), so here it is, in its full wikipedia glory. @list .= pick(*) until [<=] @list Here's a somewhat more complete example, that you can actually run: my @list = 1, 2, 7, 4, […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/\" \/>\n<meta property=\"og:site_name\" content=\"Random hacking\" \/>\n<meta property=\"article:published_time\" content=\"2010-05-31T14:50:42+00:00\" \/>\n<meta name=\"author\" content=\"cosimo\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"cosimo\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/\"},\"author\":{\"name\":\"cosimo\",\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/#\/schema\/person\/c443bedbf6ecf99550d6395620801df1\"},\"headline\":\"A working bogosort in Perl6\",\"datePublished\":\"2010-05-31T14:50:42+00:00\",\"dateModified\":\"2010-05-31T14:50:42+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/\"},\"wordCount\":360,\"commentCount\":0,\"publisher\":{\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/#\/schema\/person\/c443bedbf6ecf99550d6395620801df1\"},\"keywords\":[\"array\",\"bogosort\",\"perl\",\"perl6\",\"rakudo\",\"sort\",\"wikipedia\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/\",\"url\":\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/\",\"name\":\"A working bogosort in Perl6 - Random hacking\",\"isPartOf\":{\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/#website\"},\"datePublished\":\"2010-05-31T14:50:42+00:00\",\"dateModified\":\"2010-05-31T14:50:42+00:00\",\"breadcrumb\":{\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/2010\/05\/a-working-bogosort-in-perl6\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/www.streppone.it\/cosimo\/blog\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"A working bogosort in Perl6\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/www.streppone.it\/cosimo\/blog\/#website\",\"url\":\"https:\/\/www.streppone.it\/cosimo\/blog\/\",\"name\":\"Random hacking\",\"description\":\"Assume nothing. 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