A gentle introduction to functional programming

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING ENGINEERING MEETUP - 20TH APRIL 2020 Luca Di Stefano, Luca Ruzzola, Stefano Armenes

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING WHY?

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Pillars - referential transparency - function composition - no side-eﬀects

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING No side-eﬀects, really? - any operation that interacts with an external system - out-of-scope resources mutations - exceptions

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING ANYTHING IS A FUNCTION …or better, an expression!

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Referential transparency is all about expression Is this function referential transparent?

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Referential transparency is all about expression and what about this?

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Referential transparency is all about expression and what about this?

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Pure function A pure function is a function that, given the same input, always returns the same output without producing any side-effect.

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Pure function A pure function is a function that, given the same input, always returns the same output without producing any side-effect. Beneﬁts - readability - parallelisation - memoization - more testable

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING We can compose two functions f and g when f domain is a subset of g domain. f ∘ g === f(g(x)) Composing functions

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Composing functions …but, we are missing somethings! We can compose two functions f and g when f domain is a subset of g domain. f ∘ g === f(g(x))

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Partial functions We want to live a world where every function is a total function Is this function total?

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Cool but, why my computation fails? Option[T]

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Either[L, R]

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A GENTLE INTRODUCTION TO FUNCTIONAL PROGRAMMING Monads are your functional design patterns! Choose what you need IO List Option Either Set Future … Try