Beyond Paradigms (Go and Python examples)

Understand language features,
 use the right patterns. Presented at ThoughtWorks Chicago.

Transcript

1. 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
2. 2 Sometimes you need a blank template.
3. 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
4. PARADIGMS Programming language categories 4
5. CALCULATOR PROGRAMMING IS IMPERATIVE 5 HP-25 TI 58C
6. HP-25 CALCULATOR PROGRAMMING LANGUAGE 6
7. A SURVEY-STYLE PROGRAMMING LANGUAGES BOOK Programming Language Pragmatics,
 4th edition (2015) Michael L. Scott 7
8. GCD ASM X86 Greatest
 common divisor in x86 Assembly (Scott, 2015) 8
9. GCD IN C, OCAML AND PROLOG 9
10. GCD IN PYTHON Imperative style Functional style 10
11. GCD IN PYTHON Imperative style Functional style 11 Bad fit for Python: no tail-call optimisation
12. ONE CLASSIFICATION 12 Programming Language Pragmatics,
 4th edition (2015) Michael L. Scott
13. ONE CLASSIFICATION (ZOOM) 13
14. ONE CLASSIFICATION (ZOOM) 14 ???
15. ANOTHER BOOK Princípios de Linguagens de Programação
 (2003) Ana Cristina Vieira de Melo Flávio Soares Corrêa da Silva 15
17. 17 Lógicas
18. CATEGORIES? Ontologies are so 1900’s 18
19. A CLASSIFICATION BASED ON HARD FACTS 19
20. A CLASSIFICATION BASED ON HARD FACTS? 20 “Noble” gases!?
21. “Ontology is overrated.” Clay Shirky 21
22. A BETTER APPROACH Fundamental Features of Programming Languages 22
23. TEACHING PROGRAMMING LANGUAGE THEORY 23
24. A PAPER PRESENTING THE APPROACH 24
25. A PAPER PRESENTING THE APPROACH 25
26. A PAPER PRESENTING THE APPROACH 26
27. A PAPER PRESENTING THE APPROACH 27
28. THEORY IN PRACTICE WITH RACKET (A SCHEME DIALECT) 28
29. DESIGN PATTERNS When languages fall short 29
30. 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
31. 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
32. 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
33. 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
37. FEATURES Core features, not mere syntax 37
38. 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
39. 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
40. 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
41. 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
42. 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
43. 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
44. STRATEGY IN GO Leveraging Go’s fundamental features 44
45. CHOOSE AN ALGORITHM AT RUN TIME 45
46. 46 CHOOSE AN ALGORITHM AT RUN TIME Context Strategy Concrete strategies
47. STRATEGY IN GO “Classic” implementation using an interface Implementation using first class functions 47
48. TESTS 48 interface/strategy_test.go Repo: https://github.com/ramalho/go-paradigma/
49. TESTS 49 interface/strategy_test.go
50. CUSTOMER AND LINE ITEMS 50 interface/store.go
51. CONTEXT YAND STRATEGY 51 interface/strategy.go
52. ONE CONCRETE STRATEGY 52 interface/store.go
53. MORE CONCRETE STRATEGIES 53 interface/store.go
54. STRATEGY WITH FIRST CLASS FUNCTIONS 54
55. TESTS WITH FUNCTIONS 55
56. CONCRETE STRATEGIES WITH FUNCTIONS 56
57. WHICH IS MORE IDIOMATIC? Interfaces x functions 57
58. INTERFACE X FIRST CLASS FUNCTIONS In the Go standard library, interfaces with a single method are common. 58
59. 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
60. STRATEGY IN PYTHON Leveraging Python’s fundamental features 60
61. CHOOSE AN ALGORITHM AT RUN TIME 61
62. 62 Context Strategy Concrete strategies CHOOSE AN ALGORITHM AT RUN TIME
63. DOCTESTS FOR CONTEXT AND ONE CONCRETE STRATEGY 63 Instance of Strategy
 is given to Order constructor
64. DOCTESTS FOR TWO ADDITIONAL CONCRETE STRATEGIES 64
65. VARIATIONS OF STRATEGY IN PYTHON Classic implementation using ABC First-class function implementation Parameterised closure implementation Parameterised callable implementation 65
66. CLASSIC STRATEGY: THE CONTEXT CLASS 66 Strategy is given to constructor Strategy is used here
67. STRATEGY ABC AND A CONCRETE STRATEGY 67
68. TWO CONCRETE STRATEGIES 68
69. FIRST-CLASS FUNCTION STRATEGY 69
70. CONTEXT: STRATEGY FUNCTION AS ARGUMENT 70 Strategy function is passed to Order constructor
71. CONTEXT: INVOKING THE STRATEGY FUNCTION 71
72. CONCRETE STRATEGIES AS FUNCTIONS 72
73. CONCRETE STRATEGIES AS FUNCTIONS (2) 73
74. PARAMETERISED STRATEGY
 WITH CLOSURE 74
75. PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 75 Promo is called with discount percent value
76. PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 76 Outer function gets percent argument Inner function carries percent binding
 in its closure
77. LAMBDA: SHORTCUT TO DECLARE INNER FUNCTION 77
78. PARAMETERISED STRATEGY
 WITH CALLABLE 78
79. PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 79 Promo is instantiated with discount percent value
80. PROMOTION AS A CALLABLE CLASS 80
81. CONCRETE STRATEGIES AS CALLABLE CONCRETE CLASSES 81
82. WHICH IS MORE IDIOMATIC? Classes x functions 82
83. 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!
84. 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
85. WRAPPING UP Learn the fundamentals 85
86. INSTEAD OF PARADIGMS… 86 A B C D E F G
87. FOCUS ON FUNDAMENTAL FEATURES 87 A B C D E F G
88. …to decide whether a particular pattern or implementation makes sense. FEATURES ARE THE BEST GUIDE… A B C D E F G + ✔ ✔ ✔ ✔ + ✔ ✔ ✔ ✔ + ✔ ✔ ✔ ✔ ✔
89. 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 *
90. Luciano Ramalho luciano.ramalho@thoughtworks.com
 Twitter: @standupdev Github: github.com/standupdev/paradigm-free Slides: speakerdeck.com/ramalho THANK YOU!