Tutorial by Examples: i

The reduce function can be used to sum the elements in a list. (reduce '+ '(1 2 3 4)) ;;=> 10 By default, reduce performs a left-associative reduction, meaning that the sum 10 is computed as (+ (+ (+ 1 2) 3) 4) The first two elements are summed first, and then that result (3) is added to...

Common Lisp already has a reverse function, but if it didn't, then it could be implemented easily using reduce. Given a list like (1 2 3) === (cons 1 (cons 2 (cons 3 '()))) the reversed list is (cons 3 (cons 2 (cons 1 '()))) === (3 2 1) That may not be an obvious use of reduce, but if we ha...

You can use curl: curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.31.3/install.sh | bash Or you can use wget: wget -qO- https://raw.githubusercontent.com/creationix/nvm/v0.31.3/install.sh | bash

To verify that nvm has been installed, do: command -v nvm which should output 'nvm' if the installation was successful.

Listing available remote versions for installation nvm ls-remote Installing a remote version nvm install <version> For example nvm install 0.10.13

To list available local versions of node through NVM: nvm ls For example, if nvm ls returns: $ nvm ls v4.3.0 v5.5.0 You can switch to v5.5.0 with: nvm use v5.5.0

Three methods are provided that offer the ability to strip leading and trailing characters from a string: str.strip, str.rstrip and str.lstrip. All three methods have the same signature and all three return a new string object with unwanted characters removed. str.strip([chars]) str.strip acts o...

To connect using java.sql.DriverManager you need a JDBC url to connect to your database. JDBC urls are database specific, but they are all of the form jdbc:<subprotocol>:<subname> Where <subprotocol> identifies the driver or database (for example postgresql, mysql, firebirdsql,...

When you deploy your app to a (Node.js-specific) hosted environment, this environment usually offers a PORT-environment variable that you can use to run your server on. Changing the port number to process.env.PORT allows you to access the application. For example, http.createServer(function(reques...

You can use the node-inspector. Run this command to install it via npm: npm install -g node-inspector Then you can debug your application using node-debug app.js The Github repository can be found here: https://github.com/node-inspector/node-inspector Debugging natively You can also debu...

strpos can be understood as the number of bytes in the haystack before the first occurrence of the needle. var_dump(strpos("haystack", "hay")); // int(0) var_dump(strpos("haystack", "stack")); // int(3) var_dump(strpos("haystack", "stackoverf...

Tips & Tricks to avoid nasty situations EC2 Instances and EBS Set IAM Roles. Unlike tags, the IAM Role is set once and for all on EC2 instanciation (even after 4 years) ! Try to identify and categorize beforehand your instances so you can give an them appropriate IAM roles. IAM Roles are ...

The intrinsic pack function packs an array into a vector, selecting elements based on a given mask. The function has two forms PACK(array, mask) PACK(array, mask, vector) (that is, the vector argument is optional). In both cases array is an array, and mask of logical type and conformable with...

trait Hello { public function sayHello() { echo 'Hello '; } } trait World { public function sayWorld() { echo 'World'; } } class MyHelloWorld { use Hello, World; public function sayExclamationMark() { echo '!'; } } $o = new My...

trait HelloWorld { public function sayHello() { echo 'Hello World!'; } } // Change visibility of sayHello class MyClass1 { use HelloWorld { sayHello as protected; } } // Alias method with changed visibility // sayHello visibility not changed class MyClass2 { u...

Any array can be quickly decomposed by assigning its elements into multiple variables. A simple example: arr = [1, 2, 3] # --- a = arr[0] b = arr[1] c = arr[2] # --- or, the same a, b, c = arr Preceding a variable with the splat operator (*) puts into it an array of all the elements that h...

Variables don't necessarily have to expand to their values - substrings can be extracted during expansion, which can be useful for extracting file extensions or parts of paths. Globbing characters keep their usual meanings, so .* refers to a literal dot, followed by any sequence of characters; it's ...

Consider this broken snippet: def foo bar = [1, 2, 3, 4].map do |x| return 0 if x.even? x end puts 'baz' bar end foo # => 0 One might expect return to yield a value for map's array of block results. So the return value of foo would be [1, 0, 3, 0]. Instead, return retu...

The following compares two files with diff using process substitution instead of creating temporary files. diff <(curl http://www.example.com/page1) <(curl http://www.example.com/page2)

This feeds a while loop with the output of a grep command: while IFS=":" read -r user _ do # "$user" holds the username in /etc/passwd done < <(grep "hello" /etc/passwd)