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Introduction to Clojure loop

Clojure has a special kind of loop, unlike other programming languages, which sets a recursion point by making use of recur, meaning recur is always associated with loop. A loop is said to be completed when the number of arguments passed to the recur is the same as the number of bindings for the loop, ensuring that the recur is in sync with the loop. There is a base case associated with every recursive function based on which the looping stops, and by making use of the loop, we are implying the compiler to try its best to optimize the code for recursion.

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loop [binding] (condition (statement) (recur (binding)))

Binding is the number of bindings for the loop, which is the same as the recur function arguments.

Flowchart

Flowchart for the working of the loop in Clojure is as follows:

Working of the loop in Clojure

The loop begins with the binding variable followed by the evaluation of the condition.

If the condition is true, the control goes to statements specified inside the condition and executes them.

If the condition is false, the loop stops.

After the execution of statements inside the condition, the control again goes to the binding variable passed as a parameter to the recur function, completing a loop and continues the execution of the loop again.

The same procedure continues until the condition is false and the loop stops.

Examples of Clojure loop

Given below are the examples of Clojure loop:

Example #1

Clojure program to demonstrate a loop using recur function to print the numbers starting from 20 decremented by 1 in every step and display it as the output on the screen.

Code:

;; defining a function called decrement to decrease the values by 1 starting from 20 (defn decrement [] (loop [y 20] (println y) (recur (- y 1))))) (decrement)

Output:

In the above program, we are defining a function called decrement to decrease the given value by one after each iteration. The binding value to the loop is 20, which is decremented by 1 in the recur function and continues till the condition that the value of the variable y is greater than 0.

Example #2

Clojure program to demonstrate a loop using recur function to print the numbers starting from 0 incremented by 1 in every step and display it as the output on the screen.

Code:

;; defining a function called increment to increase the values by 1 starting from 0 to 20 (defn increment [] (loop [y 0] (when (< y 21) (println y) (recur (+ y 1))))) (increment)

Output:

In the above program, we are defining a function called increment to increase the given value by one after each iteration. The binding value to the loop is 0, which is incremented by 1 in the recur function and continues till the condition that the value of the variable y is lesser than 21.

Example #3

Clojure program to demonstrate a loop using recur function to print the numbers starting from 2 multiplied by 2 in every step whose result continues till the value of the variable is less than 21 and displays it as the output on the screen.

Code:

;; defining a function called multiply to multiply the given value by 2 starting from 2 till the result value becomes less than 21 (defn multiply [] (loop [y 2] (when (< y 21) (println y) (recur (* y 2))))) (multiply)

Output:

In the above program, we are defining a function called multiply to multiply the given value by two after each iteration. The binding value to the loop is 2, which is multiplied by 2 in the recur function and continues until the condition that the variable y becomes lesser than 21.

Example #4

Clojure program to demonstrate a loop using recur function to print the numbers starting from 20 divided by 2 in every step whose result continues till the value of the variable is less than 1 and displays it as the output on the screen.

;; defining a function called divide to divide the given value by 2 starting from 20 till the result value becomes less than 1 (defn divide [] (loop [y 20] (println y) (recur (/ y 2))))) (divide)

Output:

In the above program, we are defining a function called divide to divide the given value by two after each iteration. The binding value to the loop is 20, which is divided by 2 in the recur function and continues till the condition that the value of the variable y becomes lesser than 1.

Example #5

Clojure program to demonstrate a loop using recur function to print the numbers starting from 20 decremented by 5 in every step and display it as the output on the screen.

Code:

;; defining a function called decrement to decrease the values by 5 starting from 20 (defn decrement [] (loop [y 20] (println y) (recur (- y 5))))) (decrement)

Output:

In the above program, we are defining a function called decrement to decrease the given value by five after each iteration. The binding value to the loop is 20, which is decremented by 5 in the recur function and continues till the condition that the value of the variable y is greater than 0.

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## Javascript Program For Finding The Length Of Loop In Linked List

In this program, we will be given a linked list that may consist of a loop and we have to find if the loop exists then what will be the size of the loop. Let’s a very famous approach to finding the length of a loop with the help of a code and discuss its time and space complexity.

Introduction to Problem

In this problem, as we have seen above we are given a linked list that may or may not contain a loop in it and we have to find the length of the loop if it exits otherwise we have to return zero as there is no loop present. We will use the Floyd loop method to find the loop and then check its size. For example, if we are given a linked list as −

And there is a loop from the node containing 8 to the node containing 4, which means 8 is connected to 4 making the loop of length 5 and we have to detect it.

Approach

In this problem, we will use the Floyd loop method to detect the loop and then we will use the concept of length finding to find the length of the loop. Let’s first see the basic steps of the problem then we will move to Floyd’s method and length method.

First, we will create the class to provide the basic structure of the nodes of the linked list and define constructors in it to initialize the node values.

Then we created a function to push the elements in the given linked list.

We have created a linked list using the above method and then we have linked the last node to another node to make a cycle in it.

Floyd’s Algorithm

In this algorithm, we traverse over the linked list and once we have entered the linked list then we cannot go out from any node. This means if we have two pointers in that linked list loop part and one pointer is moving forward with one node at a time and another is at the pace of two nodes at a time, they will meet at a certain point.

After implementing the algorithm, we will call that function and check if the loop is present or not

If the loop is present than we will call to the anther function to find the length of the loop.

Another wise we will return and print no loop is present.

Example

In the below example, we define a linked list and add 8 nodes to it. We make loop in a linked list by connecting node 8 to node 4. So it makes a loop of five nodes.

In the above code, we have traversed over the complete linked list only once and for the loop part maximum of three times which makes the time complexity linear. So the time complexity of the above code is linear that is O(N) where N is the size of the linked list.

As we are not using any extra space makes the time complexity of the program O(1).

Conclusion

In this tutorial, we have learned how to find the length of the loop present in the linked list by implementing the concepts in the JavaScript language. We have used Floyd’s loop-finding algorithm to find the loop in the given linked list and then we have just used the while loop to traverse over the loop and find its length. The time complexity of the above code is O(N) and the space complexity is O(1).

## Working Of Mixin In Typescript With Examples

Introduction to TypeScript Mixins

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Working of Mixin in Typescript with Examples

There is no particular syntax for writing mixin class as it is an extra class written to overcome the single inheritance problem, which means there is no restriction for extending a single class one at a time. Using mixin class is used in building simple partial classes, and this mixin class returns a new class. Therefore, the syntax of the mixin class cannot be defined exactly as it is a class that can take a constructor to create a class that has the functionalities of the constructor by extending the previous class and then returns a new class.

Suppose if we have two classes X and Y where class X wants to get the functionality of class Y, and this can be done using extending class X extends class Y, but in Typescript, mixins are used to extend the class Y, and therefore this function Y takes class X, and therefore it returns the new class with added functionality, and here the function Y is a mixin. In general, the mixin is a function that takes a constructor of the class to extend its functionality within the new class that is created, and this new class is returned.

The exact working of mixin can be demonstrated as a process of mixing multiple classes to a single target class, and this is done by using the “implement” keyword in Typescript for the target mixin class, which also uses some generic helper functions which helps to copy the properties of each mixin to the target mixin. But we cannot use interfaces as it can only extend the members of the class but not their implementations. Therefore, TypeScript provides mixins that help to inherit or extend from more than one class, and these mixins create partial classes and combine multiple classes to form a single class that inherits all the functionalities and properties from these partial classes.

Example of TypeScript Mixins

Different example are given below:

Example #1

Code:

console.log(" Demonstration of mixin using extends in Typescript") class Courses { name = ""; x = 0; y = 0; constructor(name: string) { this.name = name; } } return class Scaling extends Base { _scale = 1; setScale(scale: number) { this._scale = scale; } get scale(): number { return this._scale; } }; } const Institute = Scale(Courses); const numcourse = new Institute("Educba"); numcourse.setScale(3); console.log(numcourse.scale);

In the above program, we are first creating class “Courses” which we are trying to scale the number of courses in the institute but to extend this class property we are using mixin concept that is first take a constructor as to make mixin extend the class “Courses” with new functionalities and the constructor is defined using “constructor” keyword. Then to extend the class “Courses”, we need to use the keyword “extends”, which is done n the function Scale where we are extending the constructor of the class to create a new class and return that class. The output of the code can be seen in the screenshot, where we are inheriting the property setscale() by extending the constructor and creating a new class named “Institute”, which is extended by the “Course” class.

Now let us see another example where it will take multiple classes and how the mixin works.

Example #2 console.log(" Demonstration of mixin in Typescript ") class  Mathfunc{ calculate(): void { console.log("The math formula is getting executed"); } } class Variables { display(): void { console.log("The variables given are calculated and display the result"); } } class Add implements Mathfunc, Variables { a: number; b: number; constructor(a, b) { this.a = a; this.b = b; } res(): number { return this.a + this.b; } display(): void { } calculate(): void { } } function applyMixins(derivedCtor: any, baseCtors: any[]) { Object.defineProperty(derivedCtor.prototype, name, Object.getOwnPropertyDescriptor(baseCtor.prototype, name)); }); }); } applyMixins(Add, [Mathfunc, Variables]); let p: Add = new Add(9, 7); p.calculate(); p.display(); let r = p.res(); console.log("The Additin of two given numbers  is as follows:"); console.log(r);

Output:

In the above program, we can see we have classes “mathfunc”, “variables”, and “Add” where t display we are just providing “implements” keyword to extend the class properties. We are providing empty implementations which mixin helper functions will later replace. Therefore this mixin created iterate through properties of the base classes and then copy all these properties from these single classes into one single target class, and this done in the function apply mixin in the above program. Therefore we are trying to calculate the sum of two numbers where we have created a constructor with two different variables, and the result is displayed using the res() function, which returns the sum.

Conclusion

This article concludes with a demonstration of mixin in typescript where we saw how mixin works with keyword “extends” and “implements”. In this article, we saw an example of demonstrating the mixin which supports single inheritance by using these keywords in the program. We should also note that it may take much time in compiling the above approaches.

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## Learn Working Of Json In Swift With Examples

Introduction to Swift JSON

Swift JSON is used for communication of the IOS web application with the server by returning a series of formatted data or information. This formatted data organized in a proper hierarchical manner is called Swift JSON. Foundation framework that includes a class called JSONSerialization is exclusively used for converting any JSON involved within the web application into Swift data types like array, number, bool, String, and Dictionary. It is very difficult to predict the actual structure or the order in which values of JSON-based web applications will receive as part of returned data.

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There is no proper syntax for any Swift JSON it can be any resource file containing the data in an ordered manner as represented below but then indentation does matter while validating any JSON data as improper JSON input might vary and can behave differently while parsing and traversing as well.

{ "title": "some_data", "url": "any_url_can_be_included", "category": "Category_for_swift_language", "views": 25648 } How JSON works in Swift?

JSON parsing or manipulation with JSON in any programming language is a common functionality when any web application tries to communicate with the other server.

Any web application dealing with JSON data tries to decode the JSON data in an ordered manner. Swift JSON parsing is very important for any IOS developer as they will most often get acquainted with these kinds of data.

Decoding modules in swift are quite flexible and are very easy to understand without any indulgence of external API.

There are times when swift JSON containing JSONSerialization class method returns a value of any type and throws error in case the data cannot get parsed easily then a proper validation with error elicitation will be given to the user for identification of the actual exception.

Although the JSON data will get validated still there will be times when JSON may contain a single value, a response from a web application can encode an object or array as any top-level object for manipulation.

All the data types related to swift get used as per requirement and any optional value can be considered for it.

There is quite a need to create Model objects from the Model-view-controller design pattern that are often used to convert json data to objects which are specific to the application’s domain in a model view.

If the applications are related to one or more web services do not return a single, or consistent model for the representation of a model object, considering implementation of several initializers to handle all the possible representations.

JSON initializer helps a lot when it comes to extracting and getting the detailed implementation with errors and exceptions. Error Handling with error protocols helps in deserialization with the fail for protocol.

Many times, it happens that the application returns multiple endpoints for any resource that returns a single JSON response following any particular protocol.

A search endpoint may return zero or more endpoints then in that case the requested query may contain more or other metadata while presenting for the endpoint.

JSON parser plays a pivotal role in parsing as it helps in making the entire JSON data organized in a properly visualized format which gives an impression that the data can be organized in a proper manner.

Swift is the programming language that allows programmers to use and make the data ordered and visualized in a very easy and effective manner by giving an idea of proper idealization and organization for operations and manipulations.

Examples of Swift JSON

Here are the following examples mentioned below.

Example #1

This program demonstrates the JSON data where the input feed is represented as follows and the output feed after execution of the JSON parsing comes out to be shown as output. But it makes the Sample usage feed with the codeable mapping.

Code:

{ "title": "Usage of the optional Swift language.", "version": "4.0", "category": "Swift_version", "views": 25642 }

Output:

Example #2

This program demonstrates the JSON data where the input feed is represented with the same input as example 1 but with the mere difference of the fact that the JSON decoder will make use of the Object mapper for conversion of JSON String to model. This is shown in the output as shown:

Code:

{ "title": "Usage of the optional Swift language.", "version": "4.0", "category": "Swift_version", "views": 25642 }

Output:

Example #3

This program demonstrates the JSON data where the input feed is represented with the same input as example 1 but with the more difference of the fact that the JSON decoder will make use of the dictionary mapper for conversion of JSON String to model. This is shown in the output as shown:

{ "title": "Usage of the optional Swift language.", "version": "4.0", "category": "Swift_version", "views": 25642 }

Output:

Example #4

This program demonstrates the custom mapping for each defined key with the mapping of a blog and key and value pairs with the JSON and making the key encoding as the main conversion of the JSON to a blog.

Code:

{ "title": "Sat_Sun_Week:end_Comboff", "version": "swift_version_4.0", "visitors_way": 258965, "posts_for_members": 62542 }

Output:

Example #5

This program demonstrates the custom mapping for each defined key with the mapping of a blog and key and value pairs with the JSON and making the Object mapper in use for representation as shown in the output.

{ "title": "Sat_Sun_Week:end_Comboff", "version": "swift_version_4.0", "visitors_way": 258965, "posts_for_members": 62542 }

Output:

Example #6

This program demonstrates the custom mapping for each defined key with the mapping of a blog, key and value pairs with the JSON and making the Dictionary mapper in use for representation as shown in the output.

Code:

{ "title": "Sat_Sun_Week:end_Comboff", "version": "swift_version_4.0", "visitors_way": 258965, "posts_for_members": 62542 }

Output:

Conclusion

Swift JSON is the proper way of validating and making the entire data set and information organized in a visualized manner for the programmers. The successful communication between any web application and server helps a lot to analyze the entire application for product analysis and division of information uniformly among all applications efficiently.

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## Working Of Bless() Function In Perl With Examples

Introduction to Perl bless function

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Working of bless() function in Perl with examples

In this article, we will discuss a built-in function where to make the program understand that the variable can be made an object of a particular class in Perl, where this function is known as the bless() function. Unlike in other programming languages, Perl creates an object similar to creating or declaring variables. Therefore the Perl programming language provides a built-in function called bless() function, which makes the variable look like an object of the particular class that it belongs to.

Now let us see the syntax and examples of how the bless() function works in the below example.

Syntax:

bless var_ref, class_name;

Parameters:

var_ref: this parameter refers to the variable as an object of the class whose class name is specified.

class_name: This parameter specifies the class name to which the object is created by marking the variable reference as an object of this class specified in this parameter.

This function can take only var_ref as an argument also, and this function returns the reference of the marked variable as a reference to an object blessed into a particular or specified class name as specified in the arguments passed to the function.

Examples

Now let us see a simple example of demonstrating the bless() function in the below section.

Example #1 use strict; use warnings; print "Demonstration of bless() function in Perl."; print "n"; print "n"; package student_data; sub stud { my \$class_name = shift; my \$var_ref = { }; print "The bless() function is now implemented:"; print "n"; bless \$var_ref, \$class_name; return \$var_ref; } print "Object creation"; print "n"; print "n"; my \$info = stud student_data("Alen","Python",32); print "The student's name is :"; print "n"; print "n"; print "The course name student taken is:"; print "n"; print "n"; print "The student's age is :"; print "n"; print "n";

Output:

In the above program, we can see we have defined class “stud” using a keyword package in Perl. Then we created a subroutine to print the student’s details. In this variable, we are referring each variable to the class name using the variable reference to object creation and class name as arguments in the bless() function in the above program. Then we are printing each value of the objects created.

Now we will see bless function taking only one argument and two arguments in the example below.

Example #2 use strict; use warnings; print "Demonstration of bless() function in Perl."; print "n"; print "n"; package student_data; sub stud { my \$class_name = shift; my \$var_ref = { }; print "The bless() function is now implemented:"; print "n"; bless \$var_ref; return \$var_ref; } package Employee; sub emp { my \$class2 = shift; my \$var_ref2 = { }; bless \$var_ref2, \$class2; return \$var_ref2; } print "Object creation"; print "n"; print "n"; print "Bless function takes only one argument:"; print "n"; print "n"; my \$info = stud student_data("Alen","Python",32); print "The student's name is :"; print "n"; print "n"; print "The course name student taken is:"; print "n"; print "n"; print "The student's age is :"; print "n"; print "n"; print "Bless() function takes two argument:"; print "n"; print "n"; my \$per_info = emp Employee("Ram", "Shukla", 343); print "The employee's name is :"; print "n"; print "n"; print "The employee's second name student taken is:"; print "n"; print "n"; print "The employee's employee number is :"; print "n"; print "n";

Output:

In the above program, we can see we have declared two classes “student_data” and “Employee” wherein the class “Student_data” we have defined function bless() with the single argument so when the variables reference is only passed, it will by default, take only the values of its current class but not of the “employee” class.

Conclusion

In this article, we conclude that the bless() function is a built-in function in Perl for marking the variables reference to object creation which belongs to the particular class with its class name specified as an argument in the bless() function. In this article, we have seen examples of bless() function taking two arguments and what happens if there are two classes and the class name is not specified as an argument in the function, which will, by default, take the current class name.

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## Working Of The 8257 Dma Controller

Initially the processor programs 8257. Here the processor behaves as the master and 8257 here works in the slave mode. The channel of the program is obtained by writing to the Address Register from the starting address of memory for transferring Data, and writing to the Counter Register where the number of bytes to be transferred is by using the Direct Memory Access Scheme. The number of bytes of information which is specified by the Least Significant 14 bits. Whereas The Most Significant 2 bits indicate what type of data transfer is to occur. After that the processor writes to the control port which intel calls as special mode register. It specifies the DMA channels which are enabled, distinguished they are fixed or rotating. When an I/O port needs DMA service, activation of the DRQ input of a channel occurs, where in turns 8257 activates the HRQ. The output of HRQ is again connected to the HOLD input of 8085 where via DMA request the HOLD input of 8085 is activated. Then 8085 completes the current machine cycle which again goes to the HOLD state. Here the address pins HOLD state the address pins, RD*, WR*, and IO/M* pins are tristate. Here 8085 is disconnected from the rest of the system. It declares that HLDA output is activated by the HOLD state.

The 8057, which was previously a slave to the 8085, by receiving commands from 8085, it becomes the master of the computer.

DMA data transfers are classified as follows −

Single-byte transfer

Short-burst mode

Long burst mode

Single-byte transfer − A DMA request for each byte of DMA data transfer used to generate by some I/O ports like Intel 8272. The following steps are performed for each byte of data transfer.

Intel 8272 activates the DRQ input of 8257.

Intel 8257 activates the HOLD input of 8085, by activating HRQ output.

Intel 8085 enters the HOLD state, suspends program in execution, and activates the HLDA output.

Intel 8257 activates the DACK* output.

Intel 8257 generates the required control signals to perform data transfer of a byte. The AR is incremented and CR is decremented.

Intel 8272 deactivates the DRQ request.

Intel 8257 deactivates the HOLD input of 8085, by deactivating the HRQ output.

Intel 8085 comes out of the HOLD state and deactivates the HLDA output.

Intel 8085 resumes suspended program for some time.

Intel 8272 reactivates the DRQ and the sequence repeated till TC is reached.

Short-burst mode − Till several bytes are transferred, some I/O ports like Intel 8275 generate a DRQ and keep it active. Depending upon how 8275 is programmed, the DRQ input of the 8257 is kept active, for up to eight DACK* activations. This results in 8 bytes of DMA data transfer. For a quite some time, the DRQ output remains inactive. The HRQ output of 8257 becomes inactive resulting in 8085 coming out of HOLD state and getting into active state, during this period. Then according to the above mentioned sequence, it is repeated till all the bytes are transferred and the TC output is activated. This kind of a data transfer is known as Short-burst mode transfer, as the DRQ input remains active till a small block of data is transferred. This scheme is used with moderately fast peripherals.

Long-burst mode − Only after all the bytes are transferred, in this mode, the DRQ request is withdrawn by the I/O port and the TC output is activated. But the DACK* output is pulsed for each byte of data transfer. This scheme is used with fast peripherals like hard disk controller.

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