Multi-Paradigm Programming and Scripting

Why Multi-Paradigm Programming and Scripting?
Universal programming constructs (invariant of language), their functions, uses and how different paradigms/languages employ them. Improved background for choosing appropriate languages:
Content of this course
Programming Constructs: The compilation process Data types (strongly-typed, weakly-typed) Pointers Variables and Invariants Conditionals (Selection) Sequence Repetition Routines Concurrency	Programming Paradigms & Languages: Abstraction (machine to very-high-level) Mark-up Imperative & Declarative Procedural Parallel & Concurrent Functional Event-Driven Multi-Paradigm Languages Interpreted Languages Comparison of all to Object Oriented Paradigm	Scripting: Interpreters and system commands Shell Scripting (Linux/UNIX) PowerShell Scripting (Windows) System Programming & Scripting	Applications of Shell Scripting: Job Control Glue Code / Wrappers Automating Tasks Data Processing / Transformation System uses I/O tasks and functions

Languages evaluation Criteria

https://www.cs.scranton.edu/~mccloske/courses/cmps344/sebesta_chap1.html

Readability	Writability	Reliability	Cost	Other criteria
This refers to the ease with which programs (in the language under consideration) can be understood. This is especially important for software maintenance. Simplicity: Orthogonality: Data Types: Syntax Design:	This is a measure of how easily a language can be used to develop programs for a chosen problem domain. Simplicity and Orthogonality: Support for Abstraction: Expressivity:	This is the property of performing to specifications under all conditions. Type Checking: Aliasing:	The following contribute to the cost of using a particular language: Training programmers: cost is a function of simplicity of language Writing and maintaining programs: cost is a function of readability and writability. Compiling programs: for very large systems, this can take a significant amount of time. Executing programs: Having to do type checking and/or index-boundary checking at run-time is expensive. There is a tradeoff between this item and the previous one (compilation cost), because optimizing compilers take more time to work but yield programs that run more quickly. Language Implementation System: e.g., Java is free, Ada not Lack of reliability: software failure could be expensive (e.g., loss of business, liability issues)	Portability: the ease with which programs that work on one platform can be modified to work on another. This is strongly influenced by to what degree a language is standardized. Generality: Applicability to a wide range of applications. Well-definedness: Completeness and precision of the language's official definition.

Imperative versus declarative code

https://medium.com/front-end-weekly/imperative-versus-declarative-code-whats-the-difference-adc7dd6c8380

Imperative paradigm

Procedural and object-oriented programming belong under imperative paradigm that you know from languages like C, C++, C#, PHP, Java and of course Assembly.

Your code focuses on creating statements that change program states by creating algorithms that tell the computer how to do things. It closely relates to how hardware works. Typically your code will make use of conditinal statements, loops and class inheritence.

Example of imperative code in JavaScript is:

class Number {

    constructor (number = 0) {
        this.number = number;
    }
  
    add (x) {
        this.number = this.number + x;
    }
    
}

const myNumber = new Number (5);
myNumber.add (3);
console.log (myNumber.number); // 8

Declarative paradigm

Logic, functional and domain-specific languages belong under declarative paradigms and they are not always Turing-complete (they are not always universal programming languages). Examples would be HTML, XML, CSS, SQL, Prolog, Haskell, F# and Lisp.

Declarative code focuses on building logic of software without actually describing its flow. You are saying what without adding how. For example with HTML you use to tell browser to display an image and you don’t care how it does that.

Example of declarative code in JavaScript is:

const sum = a => b => a + b;
console.log (sum (5) (3)); // 8

Compilation vs Interpretation

https://medium.com/@DHGorman/a-crash-course-in-interpreted-vs-compiled-languages-5531978930b6

https://guide.freecodecamp.org/computer-science/compiled-versus-interpreted-languages/

Speaking simplistically, compiled languages are those which are written in one language and, before being run, translated or "compiled" into another language, called the target language (typically in machine language that the processor can execute). Once the translation is complete, the executable code is either run or set aside to run later. Some common compiled languages include C, C++, Delphi and Rust.

The compiler translates the high-level source program into an equivalent target program (typically in machine language).

The alternative to using a compiler (for a compiled language) is using an interpreter (for interpreted languages). Interpreted languages are "interpreted" live in their original source code, although in reality they are merely compiled at runtime. What this allows for is a lot more flexibility, especially when it comes to a program adaptively modifying its structure. This flexibility does have a cost; interpreted languages are considered significantly slower.

Interpreters will run through a program line by line and execute each command.

Advantages and Disadvantages

Compiled Languages:

• Advantages:

• Programs compiled into native code at compile time usually tend to be faster than those translated at run time, due to the overhead of the translation process.

• Disadvantages:

• Additional time needed to complete the entire compilation step before testing, and Platform dependence of the generated binary code.

Interpreted Languages:

• Advantages:

• An Interpreted language gives implementations some additional flexibility over compiled implementations. Because interpreters execute the source program code themselves, the code itself is platform independent (Java’s byte code, for example). Other features include dynamic typing, and smaller executable program size.

• Disadvantages:

• The most notable disadvantage is typical execution speed compared to compiled languages.

Interpreted languages were once known to be significantly slower than compiled languages. But, with the development of just-in-time compilation, that gap is shrinking.

Phases of Compilation

Object-Oriented Paradigm

C++ Inheritance

https://www.w3schools.com/cpp/cpp_inheritance.asp

https://www.tutorialspoint.com/cplusplus/cpp_interfaces.htm

Difference Between Static and Dynamic Binding

https://techdifferences.com/difference-between-static-and-dynamic-binding.html

Reflection

A programming language that supports reflection allows its programs to have runtime access to their types and structure and to be able to dynamically modify their behavior

• The types and structure of a program are called metadata

• The process of a program examining its metadata is called introspection

• Interceding in the execution of a program is called intercession

Uses of reflection for software tools:

• Class browsers need to enumerate the classes of a program
• Visual IDEs use type information to assist the developer in building type correct code
• Debuggers need to examine private fields and methods of classes
• Test systems need to know all of the methods of a class

Downsides of Reflection:

• Performance costs
• Exposes private fields and methods
• Voids the advantages of early type checking
• Some reflection code may not run under a security manager, making code nonportable

Reflection in Java

• Limited support from java.lang.Class

• Java runtime instantiates an instance of Class for each object in the program

• The getClass method of Class returns the Class object of an object

float[] totals = new float[100];

Class fltlist = totals.getClass();

Class stg = "hello".getClass();

• If there is no object, use class field:

Class stg = String.class;

• Class has four useful methods:

getMethod searches for a specific public method of a class

getMethods returns an array of all public methods of a class

getDeclaredMethod searches for a specific method of a class

getDeclaredMethods returns an array of all methods of a class

The Method class defines the invoke method, which is used to execute the method found by getMethod

Some tutorials

Examples from Introduction to Programming Using Python 3

http://www.cs.armstrong.edu/liang/py/ExampleByChapters.html

C++ tutorial

http://www.cplusplus.com/doc/tutorial/program_structure/