Try this: def recursive_generator(lis): yield lis[0] yield from recursive_generator(lis[1:]) for k in recursive_generator([6,3,9,1]): print(k) I should point out this doesn’t work because of a bug in your function. It should probably include a check that lis isn’t empty, as shown below: def recursive_generator(lis): if lis: yield lis[0] yield from recursive_generator(lis[1:]) In case you are on … Read more
This requires a very basic recursive function to parse the child/parent pairs to a tree structure and another recursive function to print it out. Only one function would suffice but here’s two for clarity (a combined function can be found at the end of this answer). First initialize the array of child/parent pairs: $tree = … Read more
There’s code in one reply that spells it out, but you might find it easier to start from the bottom up, by asking and answering tiny questions (this is the approach in The Little Lisper): What is the reverse of null (the empty list)? null. What is the reverse of a one element list? the … Read more
Dir.glob(“**/*/”) # for directories Dir.glob(“**/*”) # for all files Instead of Dir.glob(foo) you can also write Dir[foo] (however Dir.glob can also take a block, in which case it will yield each path instead of creating an array). Ruby Glob Docs
The French and British descendants of the original ML made different choices and their choices have been inherited through the decades to the modern variants. So this is just legacy but it does affect idioms in these languages. Functions are not recursive by default in the French CAML family of languages (including OCaml). This choice … Read more
A real world example of recursion
I found this Q/A very interesting, since it provides several different solutions for the same problem. I took all these functions and tested them with a complex dictionary object. I had to take two functions out of the test, because they had to many fail results and they did not support returning lists or dicts … Read more
Get all the files and folders in a directory, don’t call function when you have . or … Your code : <?php function getDirContents($dir, &$results = array()) { $files = scandir($dir); foreach ($files as $key => $value) { $path = realpath($dir . DIRECTORY_SEPARATOR . $value); if (!is_dir($path)) { $results[] = $path; } else if ($value … Read more
To answer your specific question: No, from the standpoint of learning a language, recursion isn’t a feature. If your professor really docked you marks for using a “feature” he hadn’t taught yet, that was wrong. Reading between the lines, one possibility is that by using recursion, you avoided ever using a feature that was supposed … Read more
WITH q AS ( SELECT * FROM mytable WHERE ParentID IS NULL — this condition defines the ultimate ancestors in your chain, change it as appropriate UNION ALL SELECT m.* FROM mytable m JOIN q ON m.parentID = q.PersonID ) SELECT * FROM q By adding the ordering condition, you can preserve the tree order: … Read more