Beyond Paradigms (Go and Python examples)

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E x a m p l e s i n P y t h o n a n d G o BEYOND PARADIGMS Understand language features,  use the right patterns. Luciano Ramalho @ramalhoorg

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2 Sometimes you need a blank template.

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FLUENT PYTHON, MY FIRST BOOK Fluent Python (O’Reilly, 2015) Python Fluente (Novatec, 2015) Python к вершинам  мастерства (DMK, 2015) 流暢的 Python (Gotop, 2016) also in Polish, Korean, etc… 3 4.7 stars at  Amazon.com

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PARADIGMS Programming language categories 4

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CALCULATOR PROGRAMMING IS IMPERATIVE 5 HP-25 TI 58C

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HP-25 CALCULATOR PROGRAMMING LANGUAGE 6

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A SURVEY-STYLE PROGRAMMING LANGUAGES BOOK Programming Language Pragmatics,  4th edition (2015) Michael L. Scott 7

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GCD ASM X86 Greatest  common divisor in x86 Assembly (Scott, 2015) 8

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GCD IN C, OCAML AND PROLOG 9

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GCD IN PYTHON Imperative style Functional style 10

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GCD IN PYTHON Imperative style Functional style 11 Bad ﬁt for Python: no tail-call optimisation

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ONE CLASSIFICATION 12 Programming Language Pragmatics,  4th edition (2015) Michael L. Scott

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ONE CLASSIFICATION (ZOOM) 13

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ONE CLASSIFICATION (ZOOM) 14 ???

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ANOTHER BOOK Princípios de Linguagens de Programação  (2003) Ana Cristina Vieira de Melo Flávio Soares Corrêa da Silva 15

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17 Lógicas

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CATEGORIES? Ontologies are so 1900’s 18

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A CLASSIFICATION BASED ON HARD FACTS 19

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A CLASSIFICATION BASED ON HARD FACTS? 20 “Noble” gases!?

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“Ontology is overrated.” Clay Shirky 21

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A BETTER APPROACH Fundamental Features of Programming Languages 22

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TEACHING PROGRAMMING LANGUAGE THEORY 23

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A PAPER PRESENTING THE APPROACH 24

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A PAPER PRESENTING THE APPROACH 25

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A PAPER PRESENTING THE APPROACH 26

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A PAPER PRESENTING THE APPROACH 27

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THEORY IN PRACTICE WITH RACKET (A SCHEME DIALECT) 28

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DESIGN PATTERNS When languages fall short 29

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GOF: CLASSIC BOOK BY THE “GANG OF FOUR” Design Patterns: Elements of Reusable Object-Oriented Software (1995) Erich Gamma  Richard Helm  Ralph Johnson  John Vlissides 30

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NOT EVERY PATTERN IS UNIVERSAL Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley, 1995), p. 4. 31

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NOT EVERY PATTERN IS UNIVERSAL Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley, 1995), p. 4. 32

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NOT EVERY PATTERN IS UNIVERSAL Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley, 1995), p. 4. 33

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FEATURES Core features, not mere syntax 37

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SAMPLE FEATURES ✖ LANGUAGES 38 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 39 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural Functions as objects Classes as objects

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SAMPLE FEATURES ✖ LANGUAGES 40 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 41 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 42 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 43 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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STRATEGY IN GO Leveraging Go’s fundamental features 44

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CHOOSE AN ALGORITHM AT RUN TIME 45

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46 CHOOSE AN ALGORITHM AT RUN TIME Context Strategy Concrete strategies

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STRATEGY IN GO “Classic” implementation using an interface Implementation using ﬁrst class functions 47

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TESTS 48 interface/strategy_test.go Repo: https://github.com/ramalho/go-paradigma/

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TESTS 49 interface/strategy_test.go

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CUSTOMER AND LINE ITEMS 50 interface/store.go

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CONTEXT YAND STRATEGY 51 interface/strategy.go

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ONE CONCRETE STRATEGY 52 interface/store.go

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MORE CONCRETE STRATEGIES 53 interface/store.go

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STRATEGY WITH FIRST CLASS FUNCTIONS 54

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TESTS WITH FUNCTIONS 55

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CONCRETE STRATEGIES WITH FUNCTIONS 56

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WHICH IS MORE IDIOMATIC? Interfaces x functions 57

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INTERFACE X FIRST CLASS FUNCTIONS In the Go standard library, interfaces with a single method are common. 58

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INTERFACE X FIRST CLASS FUNCTIONS But the http package supports both styles 59 *Kumar Iyer (ThoughtWorks): Higher-order functions vs interfaces in golang http://bit.ly/2j39uKh

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STRATEGY IN PYTHON Leveraging Python’s fundamental features 60

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CHOOSE AN ALGORITHM AT RUN TIME 61

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62 Context Strategy Concrete strategies CHOOSE AN ALGORITHM AT RUN TIME

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DOCTESTS FOR CONTEXT AND ONE CONCRETE STRATEGY 63 Instance of Strategy  is given to Order constructor

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DOCTESTS FOR TWO ADDITIONAL CONCRETE STRATEGIES 64

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VARIATIONS OF STRATEGY IN PYTHON Classic implementation using ABC First-class function implementation Parameterised closure implementation Parameterised callable implementation 65

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CLASSIC STRATEGY: THE CONTEXT CLASS 66 Strategy is given to constructor Strategy is used here

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STRATEGY ABC AND A CONCRETE STRATEGY 67

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TWO CONCRETE STRATEGIES 68

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FIRST-CLASS FUNCTION STRATEGY 69

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CONTEXT: STRATEGY FUNCTION AS ARGUMENT 70 Strategy function is passed to Order constructor

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CONTEXT: INVOKING THE STRATEGY FUNCTION 71

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CONCRETE STRATEGIES AS FUNCTIONS 72

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CONCRETE STRATEGIES AS FUNCTIONS (2) 73

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PARAMETERISED STRATEGY  WITH CLOSURE 74

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PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 75 Promo is called with discount percent value

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PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 76 Outer function gets percent argument Inner function carries percent binding  in its closure

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LAMBDA: SHORTCUT TO DECLARE INNER FUNCTION 77

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PARAMETERISED STRATEGY  WITH CALLABLE 78

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PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 79 Promo is instantiated with discount percent value

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PROMOTION AS A CALLABLE CLASS 80

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CONCRETE STRATEGIES AS CALLABLE CONCRETE CLASSES 81

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WHICH IS MORE IDIOMATIC? Classes x functions 82

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WHICH IS MORE IDIOMATIC? Classic strategy feels too verbose for Python* First-class functions are very common in the standard library •The sorted built-in key argument is one example. 83 * Yes, this is subjective. I am talking about style!

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WHICH IS MORE IDIOMATIC — WITH PARAMETER? Use of closure is common in Python •nonlocal was added in Python 3 to support it better Callable objects are uniquely Pythonic •Graham Dumpleton recommends callable classes as the best way to code decorators 84

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WRAPPING UP Learn the fundamentals 85

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INSTEAD OF PARADIGMS… 86 A B C D E F G

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FOCUS ON FUNDAMENTAL FEATURES 87 A B C D E F G

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…to decide whether a particular pattern or implementation makes sense. FEATURES ARE THE BEST GUIDE… A B C D E F G + ✔ ✔ ✔ ✔ + ✔ ✔ ✔ ✔ + ✔ ✔ ✔ ✔ ✔

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WHY LEARN THE FUNDAMENTALS* Learn new languages faster Leverage language features Choose among alternative implementations Make good use of design patterns Emulate missing features when they are missing 89 Inspired by Programming Language Pragmatics Michael L. Scott *

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Luciano Ramalho luciano.ramalho@thoughtworks.com  Twitter: @standupdev Github: github.com/standupdev/paradigm-free Slides: speakerdeck.com/ramalho THANK YOU!