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This story is a part of — My CS Notebook

Functional Programming

Pure Functions

o   Given the same input will always return the same output

Recursion

o   Must have a base criterion – a condition in which when met, closes the recursion and returns a result
o   Must actively move toward the base criterion
o   Often a function will call itself carrying the latest value to the next call via method signature or parameters until the base criterion is met

Referential Transparency (Substitution Principle)

o   States that you can replace a value in an expression without changing its behavior
o   Templating Syntax or Interpolation would fall under this category

Functions are First Class & Can Be Higher Order

This means that functions come first over other structure principles, for example in Java classes come first and methods / functions are encapsulated by classes.

Higher Order Function is defined as meeting one of the following
- Takes in functions as arguments
- Returns a function

CS Stuff

Model View Controller (MVC)

o   Model: Structures data in a reliable way
o   View: Displays data in an easy to understand format
o   Controller: Takes in commands to the model for data updates and send instructions to the view to update
o   Support modularity and reusability

Namespaces

o   “named” program regions used to limit the scope of variable, functions, or classes within a program
o   Help avoid conflict with existing definitions
o   Help support encapsulation

Interpreter

o   Translate program one line at a time
o   Increased analysis efficiency
o   Decreased execution efficiency
o   Require less Space Complexity
o   JavaScript, Python, and Ruby use interpreters

Compiler

o   Translate Entire Program
o   Decreased analysis efficiency
o   Increased execution efficiency
o   Require more Space Complexity
o   C, C++, and Java use compilers
o   Umbrella term to describe when the code of one program is processes into another language
o   Example: In C using gcc “compiles” C source code into machine language

Transpiler

o   Translate Entire Program
o   Similar to a compiler in that it takes one source code and processes it into another
o   Almost a subset of a compiler
o   The output of a transpiler still has to go through a Compiler or Interpreter
o   Example:
- Babel: Transpiles ES6 JavaScript to ES5 JavaScript
- Emscripten: Transpiles C/C++ to JavaScript

Runtime Environment

o   When a program is executed it is in a “runtime state”
o   In this state, the program communicates with the hardware and accomplishes tasks

Call Stack

o   Mechanism for an interpreter to keep track of its place within a script that call multiple functions
o   FILO, stack implemented in a runtime environment
o   Data structure that records place of current execution
o   Similar to Heap but varies:
- Stack data structure (linear)
- Fast access
- Only supports local variable
- Limit on memory allocation
- Immutable
- Memory allocated contiguously

Assembly Language

o   Low-level programming language
o   Indented to directly communicate with computer hardware
o   Differs from machine language in that it is designed to be human readable
o   In general, assembly languages acts as a bridge between software and hardware

Machine Language

o   Low-level programming language
o   Indented to directly communicate with computer hardware
o   Consists of binary and hexadecimal character

Runtimes

o   Synchronous--Blocks next operation until current operation is complete
o   Asynchronous--Can execute another task before the current task is complete

Scoping

Dynamic Scope
§  Not very common: Mathematica, Lisp, Lua
Lexical / Static Scope
§  Common to most programming languages
§  Set the range of functionality of a variable to that it can only be referenced from within the block of code in which it is defined
§  Scope can be broken into Built-in, Global, Enclosed, and Local
§  Closure is when a block or function closes it attributes to only to modifiers that are within the block of code itself
§  Pretty much every modern language uses Lexical Scoping

Memory Heap

o   Can be used in parity with a Call Stack in a runtime environment
o   Similar to a Call Stack but varies:
- Heap data structure (hierarchical)
- Slower access
- Often supports global variables whereas a call stack only holds the local scope of the current executions
- No limit on memory allocations
- Mutable
- Memory allocated randomly

Concurrency & Parallelism

o   Concurrency is executing multiple tasks at the same time, but not simultaneously.
- Two or more tasks work in overlapping time periods

Threading & Processes

o   Threads -> sequence of code execution which are independent of one another
o   Process -> the instance of a running program. A program can be multiprocessor
o   If you want to use more than more than one core in a CPU you will want to use multiprocessing
- By default Java and C do this
- Python has a Global Interpreter Lock (GIL) built in to prevent more than one thread from interpreting Python. This however can be overridden with Python’s built-in multiprocessing module
o    Single Threaded Language
Limits runtime environment to 1 call stack and 1 memory heap

Big Data

Systems

• Centralized — Old school UPS logistics but with computers
• Decentralized — Two or more centralized systems that can communicate
• Distributed — Web of systems, think current Amazon.com logistics

MapReduce

• A big part of how queries work on scaled data infrastructure that lives on distributed systems.

o   Processing large data sets in a distributed fashion over several machines
o   Mapping dataset into a collection of <key, value> pairs, and then reducing over all pairs with the same key
o   A map reduce is split into two scripts
- A mapping script
- A reduce script
o   A map reduce execution utilize the divide and conquer methodology over a distributed computing structure.

Hadoop (Popular Data Platform)

Framework for Big Data
§  Contains two modules
- MapReduce
- Hadoop Distributed File System (HDFS)
Uses Sub-Projects
§  Hive -- SQL like scripts to preform MapReduce Functions
§  Sqoop -- Import Export data to and from HDFS and (Relational Database Management System) RDBMS
§  Pig -- procedural language to develop scripts for MapReduce Operations

Hadoop Structure

What is it that makes Hadoop so valuable for Big Data?

• A traditional database like MySQL has similar components to Hadoop. There is a query language, that query language directs the database architecture to find the data (I/O) and the metadata (Model) attached to it.

• Hadoop is special because it separates the metadata layer from the data (increasing the abstraction of the design) and utilizes AWS S3’s existing distributed computing structure.

Languages / Tools

GoLang

Aim to replace C++ and Java by:
§  Increasing compilation efficiency
§  Increasing execution efficiency
§  Increase / Support readability
§  Increasing consistency
§  Allow development in multiple languages
§  Allowing easier maintenance of dependencies
Special Sauce:
§  Multithreading & Concurrency
·      GoLang aims to keep pace with hardware changes that allow for more threading and concurrent efficiency
§  Compilation Efficiency
- Go is a compiled language like C/C++
- It also does garbage collection and object removal like Java
§  Unmatched Simplicity
- No Templates
- Single Executable – No Runtime Engine Needed
- No Built in Libraries
§  Built-in Testing Framework and Profiling
§  Easy Learning Curve

Scala

o   Mis of OOP and Functional Programming
o   Can be used for Machine Learning to Web Apps

C/C++

• Synchronous / Multithreaded / Semi-OOP
• Low-level, used everywhere:

Linux, Mac, Word, Everything, PHP, Perl, Video Games, BLoomber, MySQL, Microsoft OS

.NET / C# / F# / Visual Basic

• Video that explains it all: https://www.youtube.com/watch?v=bEfBfBQq7EE&t=624s

Java

• Synchronous / Multithreaded / OOP

Use cases: Applets, Applications, Server Suites, Open Source, Apache, Mobile apps, etc.

JavaScript

• single-threaded, non-blocking, and concurrent

o   Async is possible because under the hood, JavaScript engines use multithreaded languages like C++ (Chrome) & Rust (Firefox)
o   JavaScript is a interpreted language and requires an engine to convert it into machine code.
o   V8 and engine / interpreter (used in Node and Chrome) does this.
Contains: a memory heap, Call Stack, Event loop, Callback queue

PHP

o   Hypertext Preprocessor
o   Useful for web development
o   WordPress
o   Lamp Stack (Linux, Apache, MySQL, PHP)
o   Laravel is a PHP framework (for Web Artisans!)

HTML/CSS (Web-centric)

Hypertext Markup Language
Cascading Style Sheets

Python

• Synchronous / Single-Threaded / Semi-OOP

Elm

o   Language designed to transpiled into JavaScript
o   It is impossible to leave a problem unhandled
o   Immutable
o   Maintainable
o   Highly readable

Ruby On Rails

• MVC framework
• Used by Twitter
• Check out: https://www.netguru.com/blog/what-is-ruby-on-rails-used-for

XML / JSON

Same
§  Self-Describing
§  Hierarchical
§  Can be used by a large amount of languages
§  Can be fetched with an HttpRequest
Different
§  JSON doesn’t use tags
§  JSON is shorter
§  JSON is quicker to read and write
§  JSON can use arrays

This story is a part of — My CS Notebook

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