Functional programming - part 1

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Functional programming James Su - 2022/04/15 Sur f ing in the changing world

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What is functional programming?

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Functional programming in Wikipedia • A programming paradigm characterized by mathematical functions and the avoidance of side e ff ects. • A programming style that uses only pure functions without side e ff ects.

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Side effects Anything a function does other than returning a value

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Pure functions Don't have any side e ff ects. Given the same arguments, return the same result.

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Bene f its of pure functions • Don't depend on how many times and when they are run. • Results are predictable, easier to understand and control. • Compilers can optimize for predictable things.

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But, we need side effects in real world • Send an email • Reading a f ile • Writing to database • Making a web request • Blinking a light

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Functional programming in real world • A set of skills, concepts and principles: • Distinguishing actions, calculations, and data • Staying immutable in a mutable language • ... and more • They are valuable and regardless of what language you use.

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Distinguishing Actions, Calculations and Data

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Actions • Depend on how many times or when it is run. • Also called: functions with side e ff ects. • Examples: • Send an email • Read from a database

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Calculations • Computations from input to output. • Also called: pure functions, mathematical functions. • Examples: • Find the users to send email • Calculate total price in shopping cart

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Data • Facts about events. • Their meanings are di ff erent according to situations. • Examples: • An email address • A user structure • A dinner receipt

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Bene f its of distinguishing actions, calculations and data • Thinking about a problem • Clarify parts that need special attention (actions) • What data we will need to capture (data) • What decisions we will need to make (calculations) • Coding a solution • Write code with immutable in mind: data > calculations > actions. • Reading code • Refactor the code to better separate from actions, calculations and data.

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Thinking a problem

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Thinking a problem

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Strati f ied design Organizing code by "rate of change"

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Why functional programming popular these days?

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Functional languages • Erlang • WhatsApp - Why WhatsApp Only Needs 50 Engineers for Its 900M Users • Elixir • Discord - How Discord Scaled Elixir to 5,000,000 Concurrent Users • Apple - Working on APIs towards carbon neutral by 2030 • Clojure • Roam Research - State of Clojure 2021 Results • Elm • https://github.com/jah2488/elm-companies • Blazing Fast HTML

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We are in a world programs run on multicores and distributed devices • Functional programs run in parallel. • Compilers optimize for functional programs.