Tutorial by Examples: e

Macros return code. Since code in Lisp consists of lists, one can use the regular list manipulation functions to generate it. ;; A pointless macro (defmacro echo (form) (list 'progn (list 'format t "Form: ~a~%" (list 'quote form)) form)) This is often very hard to...

The expansion of a macro often needs to use symbols that weren't passed as arguments by the user (as names for local variables, for example). One must make sure that such symbols cannot conflict with a symbol that the user is using in the surrounding code. This is usually achieved by using GENSYM, ...

json.Marshal from the package "encoding/json" encodes a value to JSON. The parameter is the value to encode. The returned values are an array of bytes representing the JSON-encoded input (on success), and an error (on failure). decodedValue := []string{"foo", "bar"} ...

json.Unmarshal from the package "encoding/json" decodes a JSON value into the value pointed by the given variable. The parameters are the value to decode in []bytes and a variable to use as a storage for the de-serialized value. The returned value is an error (on failure). encodedValue :...

After following the instructions above and installing Leiningen, start a new project by running: lein new <project-name> This will setup a Clojure project with the default Leiningen template within the <project-name> folder. There are several templates for Leiningen, which affect the...

Given some default routing such as {controller=Home}/{action=Index}/{id?} if you had the url https://stackoverflow.com/questions/1558902 This would go to the QuestionsController and the value 1558902 would be mapped to an id parameter of an index action, i.e. public ActionResult Index(int? id){ ...

To extend on the route binding say you had a url like https://stackoverflow.com/questions/1558902?sort=desc and routing like {controller=Home}/{action=Index}/{id?} public ActionResult Index(int? id, string sort){ //sort would bind to the value in the query string, i.e. "desc" } ...

Often you'd be working with viewmodel classes in asp.net-mvc and would want to bind to properties on these. This works similar to mapping to individual parameters. Say you had a simple view model call PostViewModel like this public class PostViewModel{ public int Id {get;set;} public int Sn...

Functions in Common Lisp are first class values. An anonymous function can be created by using lambda. For example, here is a function of 3 arguments which we then call using funcall CL-USER> (lambda (a b c) (+ a (* b c))) #<FUNCTION (LAMBDA (A B C)) {10034F484B}> CL-USER> (defvar *fo...

Any symbol in Common Lisp has a slot for a variable to be bound and a separate slot for a function to be bound. Note that the naming in this example is only for illustration. Global variables should not be named foo, but *foo*. The latter notation is a convention to make it clear that the variable ...

Common Lisp contains many higher order functions which are passed functions for arguments and call them. Perhaps the most fundamental are funcall and apply: CL-USER> (list 1 2 3) (1 2 3) CL-USER> (funcall #'list 1 2 3) (1 2 3) CL-USER> (funcall #'list 1 2 3 4 5) (1 2 3 4 5) CL-USER&g...

Introduction In this minimalist example, using pytest we're going to test that indeed our Hello World app does return "Hello, World!" with an HTTP OK status code of 200, when hit with a GET request on the URL / First let's install pytest into our virtualenv pip install pytest And jus...

SELECT * FROM Employees This statement will return all the rows from the table Employees. Id FName LName PhoneNumber ManagerId DepartmentId Salary Hire_date CreatedDate ModifiedDate 1 James Smith 1234567890 NULL 1 1000 01-01-2002 0...

os.access is much better solution to check whether directory exists and it's accesable for reading and writing. import os path = "/home/myFiles/directory1" ## Check if path exists os.access(path, os.F_OK) ## Check if path is Readable os.access(path, os.R_OK) ## Check if path i...

Multiple transforms can be applied to an element in one property like this: transform: rotate(15deg) translateX(200px); This will rotate the element 15 degrees clockwise and then translate it 200px to the right. In chained transforms, the coordinate system moves with the element. This means tha...

The break statement ends a loop (like for, while) or the evaluation of a switch statement. Loop: while(true) { if(someCondition == 5) { break; } } The loop in the example would run forever. But when someCondition equals 5 at some point of execution, then the loop ends. If mult...

h2 { /* adds a 1px space horizontally between each letter; also known as tracking */ letter-spacing: 1px; } The letter-spacing property is used to specify the space between the characters in a text. ! letter-spacing also supports negative values: p { letter-spacing: -1px; }...

When reading multiple values from a channel, using range is a common pattern: func foo() chan int { ch := make(chan int) go func() { ch <- 1 ch <- 2 ch <- 3 close(ch) }() return ch } func main() { for n := r...

With Git, you can (almost) always turn the clock back Don't be afraid to experiment with commands that rewrite history*. Git doesn't delete your commits for 90 days by default, and during that time you can easily recover them from the reflog: $ git reset @~3 # go back 3 commits $ git reflog c4...

Elements can be selected by jQuery using jQuery Selectors. The function returns either an element or a list of elements. Basic selectors $("*") // All elements $("div") // All <div> elements $(".blue") ...