Tutorial by Examples: s

Sometimes you want to destructure key under a map which might not be present in the map, but you want a default value for the destructured value. You can do that this way: (def my-map {:a 3 :b 4}) (let [{a :a b :b :keys [c d] :or {a 1 c 2}} my-map] (println ...

Destructurling works in many places, as well as in the param list of an fn: (defn my-func [[_ a b]] (+ a b)) (my-func [1 2 3]) ;= 5 (my-func (range 5)) ;= 3 Destructuring also works for the & rest construct in the param list: (defn my-func2 [& [_ a b]] (+ a b)) (my-func2 1 ...

Destructuring also gives you the ability to interpret a sequence as a map: (def my-vec [:a 1 :b 2]) (def my-lst '("smthg else" :c 3 :d 4)) (let [[& {:keys [a b]}] my-vec [s & {:keys [c d]} my-lst] (+ a b c d)) ;= 10 It is useful for defining functions with named p...

Predicates that produce side effects leave the realm of pure logic. These are for example: writeq/1 read/1 format/2 Side effects are phenomena that cannot be reasoned about within the program. For example, deletion of a file or output on the system terminal.

Predicates that reason about instantiations are called meta-logical. Examples are: var/1 ground/1 integer/1 These predicates are outside the realm of pure monotonic logic programs, because they break properties like commutativity of conjunction. Other predicates that are meta-logical includ...

Predicates that reason about all solutions are extra-logical. These are for example: setof/3 findall/3 bagof/3

CLP(FD) constraints are completely pure relations. They can be used in all directions for declarative integer arithmetic: ?- X #= 1+2. X = 3. ?- 3 #= Y+2. Y = 1.

In oracle, the difference (in days and/or fractions thereof) between two DATEs can be found using subtraction: SELECT DATE '2016-03-23' - DATE '2015-12-25' AS difference FROM DUAL; Outputs the number of days between the two dates: DIFFERENCE ---------- 89 And: SELECT TO_DATE( '201...

The MEDIAN function since Oracle 10g is an easy to use aggregation function: SELECT MEDIAN(SAL) FROM EMP It returns the median of the values Works on DATETIME values too. The result of MEDIAN is computed by first ordering the rows. Using N as the number of rows in the group, Oracle calcula...

Following code will release the lock. There will be no problem. Behind the scenes lock statement works as try finally lock(locker) { throw new Exception(); } More can be seen in the C# 5.0 Specification: A lock statement of the form lock (x) ... where x is an expression of a referenc...

The function toupper will convert a string to upper case (capital letters). For example: BEGIN { greeting = "hello" loud_greeting = toupper(greeting) print loud_greeting } This code will output "HELLO" when run.

Given a C++ source file main.cpp defining a main() function, an accompanying CMakeLists.txt file (with the following content) will instruct CMake to generate the appropriate build instructions for the current system and default C++ compiler. main.cpp (C++ Hello World Example) #include <iostream...

We create a new concurrent process by calling the spawn function. The spawn function will get as parameter a function Fun that the process will evaluate. The return value of the spawn function is the created process identifier (pid). 1> Fun = fun() -> 2+2 end. #Fun<erl_eval.20.52032458&gt...

Enum classes can also declare members (i.e. properties and functions). A semicolon (;) must be placed between the last enum object and the first member declaration. If a member is abstract, the enum objects must implement it. enum class Color { RED { override val rgb: Int = 0xFF0000 ...

enum class Color { RED, GREEN, BLUE } Each enum constant is an object. Enum constants are separated with commas.

The routing configuration is included in your app/config/config.yml file, by default the app/config/routing.yml file. From there you can link to your own routing configuration in a bundle # app/config/routing.yml app: resource: "@AppBundle/Resources/config/routing.yml" It migh...

The routing configuration is included in your app/config/config.yml file, by default the app/config/routing.yml file. From there you can link to the controllers that have annotated routing configuration: # app/config/routing.yml app: resource: "@AppBundle/Controller" type: ...

A browser's debugging console can be used in order to print simple messages. This debugging or web console can be directly opened in the browser (F12 key in most browsers – see Remarks below for further information) and the log method of the console Javascript object can be invoked by typing the fol...

Sometimes, we may open a file which we do not have permission to write in Vim without using sudo. Use this command to save a read-only file edited in Vim. :w !sudo tee > /dev/null % Which you could map to :w!! in your .vimrc: cmap w!! w !sudo tee > /dev/null % You will be presented a ...

The size of a canvas is the area it occupies on the page and is defined by the CSS width and height properties. canvas { width : 1000px; height : 1000px; } The canvas resolution defines the number of pixels it contains. The resolution is set by setting the canvas element width and heigh...