Beyond Paradigms

Understand language features,
 use the right patterns.

Transcript

1. T h e o r y f o r p r a c t i c e 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. THE LANGUAGE LIST 18
19. LANGUAGES ARE MISSING… 19
20. LANGUAGE CATEGORIES 20
21. LANGUAGE CATEGORIES (2) 21
22. LANGUAGE CATEGORIES (3) 22
23. LANGUAGE CATEGORIES (4) 23
24. CATEGORIES? Ontologies are so 1900’s 24
25. A CLASSIFICATION BASED ON HARD FACTS 25
26. A CLASSIFICATION BASED ON HARD FACTS? 26 “Noble” gases!?
27. “Ontology is overrated.” Clay Shirky 27
28. A BETTER APPROACH Fundamental Features of Programming Languages 28
29. TEACHING PROGRAMMING LANGUAGE THEORY 29
30. A PAPER PRESENTING THE APPROACH 30
31. A PAPER PRESENTING THE APPROACH 31
32. A PAPER PRESENTING THE APPROACH 32
33. A PAPER PRESENTING THE APPROACH 33
34. THEORY IN PRACTICE WITH RACKET (A SCHEME DIALECT) 34
35. THEORY IN PRACTICE WITH PASCAL (1990) 35
36. DESIGN PATTERNS When languages fall short 36
37. 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 37
38. FAULTS IN THE SPREAD OF PATTERNS 38
39. 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. 39
40. 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. 40
41. 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. 41
46. FEATURES Core features, not mere syntax 46
47. SAMPLE FEATURES ✖ LANGUAGES 47 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
48. SAMPLE FEATURES ✖ LANGUAGES 48 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
49. SAMPLE FEATURES ✖ LANGUAGES 49 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
50. SAMPLE FEATURES ✖ LANGUAGES 50 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
51. SAMPLE FEATURES ✖ LANGUAGES 51 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
52. SAMPLE FEATURES ✖ LANGUAGES 52 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
53. STRATEGY IN PYTHON Leveraging Python’s fundamental features 53
54. CHOOSE AN ALGORITHM AT RUN TIME 54
55. 55 Context Strategy Concrete strategies CHOOSE AN ALGORITHM AT RUN TIME
56. DOCTESTS FOR CONTEXT AND ONE CONCRETE STRATEGY 56 Instance of Strategy
 is given to Order constructor
57. DOCTESTS FOR TWO ADDITIONAL CONCRETE STRATEGIES 57
58. VARIATIONS OF STRATEGY IN PYTHON Classic implementation using ABC First-class function implementation Parameterised closure implementation Parameterised callable implementation 58
59. CLASSIC STRATEGY: THE CONTEXT CLASS 59 Strategy is given to constructor Strategy is used here
60. STRATEGY ABC AND A CONCRETE STRATEGY 60
61. TWO CONCRETE STRATEGIES 61
62. FIRST-CLASS FUNCTION STRATEGY 62
63. CONTEXT: STRATEGY FUNCTION AS ARGUMENT 63 Strategy function is passed to Order constructor
64. CONTEXT: INVOKING THE STRATEGY FUNCTION 64
65. CONCRETE STRATEGIES AS FUNCTIONS 65
66. CONCRETE STRATEGIES AS FUNCTIONS (2) 66
67. PARAMETERISED STRATEGY
 WITH CLOSURE 67
68. PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 68 Promo is called with discount percent value
69. PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 69 Outer function gets percent argument Inner function carries percent binding
 in its closure
70. LAMBDA: SHORTCUT TO DECLARE INNER FUNCTION 70
71. PARAMETERISED STRATEGY
 WITH CALLABLE 71
72. PARAMETERISED STRATEGY IMPLEMENTED AS CLOSURE 72 Promo is instantiated with discount percent value
73. PROMOTION AS A CALLABLE CLASS 73
74. CONCRETE STRATEGIES AS CALLABLE CONCRETE CLASSES 74
75. WHICH IS MORE IDIOMATIC? Classes x functions 75
76. 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. 76 * Yes, this is subjective. I am talking about style!
77. 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 77
78. WRAPPING UP Learn the fundamentals 78
79. WHY LEARN THE FUNDAMENTALS* Learn new languages faster Leverage language features Choose among alternative implementations Make good use of design patterns Debug hard problems Emulate missing features when they are missing 79 Inspired by Programming Language Pragmatics Michael L. Scott *
80. Luciano Ramalho luciano.ramalho@thoughtworks.com
 Twitter: @standupdev Github: github.com/standupdev/paradigm-free Slides: speakerdeck.com/ramalho ¡GRACIAS!