Stop Coding Pascal

Languages vs. Compilers, Imperative vs. Declarative, Ideas vs. Implementation.

Transcript

1. Stop coding Pascal ...emotional sketch about past, present and future of programming languages, Python, compilers, developers, Life, Universe and Everything Saturday, April 6, 13
2. About me • Alexey Kachayev • CTO at KitApps Inc. • Open source activist • Functional programming advocate • Erlang, Python, Scala, Clojure, Go, Haskell • @kachayev • kachayev <$> gmail • github.com/kachayev/fn.py Saturday, April 6, 13
3. Einstein problem solving principle Saturday, April 6, 13
4. So, next 55 minutes we will talk about the core of the problems Saturday, April 6, 13
5. What are we going to talk about? • difference between syntax and semantic • imperative code: when and WHY? • machine VS language: problems and solutions • where did Python features come from • what is the current problem • why should I care? Saturday, April 6, 13
6. Simple task count of unique substring Saturday, April 6, 13
7. Pascal Saturday, April 6, 13
8. * just sample... it’s really hard to show Pascal version in slide Saturday, April 6, 13
9. Python v.1 Saturday, April 6, 13
10. Python v.2 Saturday, April 6, 13
11. Haskell Saturday, April 6, 13
12. What the difference is? • “pascal” VS “python.v1” - syntax (mostly) • “python.v1” VS “python.v2” - semantic • “python.v2” VS “haskell” - (mostly) syntax (*) * iterators VS. lazy-evaluation is a different story Saturday, April 6, 13
13. Let’s dig deeper Saturday, April 6, 13
14. Why is Haskell code so compact? • transformations • compositions • * unix way, BTW Saturday, April 6, 13
15. Where did all these i, j, k come from? Saturday, April 6, 13
16. Instructions Transformations VS. Saturday, April 6, 13
17. ... and deeper Saturday, April 6, 13
18. λ-calculus Turing machine VS. Saturday, April 6, 13
19. Turing machine • infinite memory • instructions (finite) Saturday, April 6, 13
20. λ - calculus • terms • abstraction • application • β-reduction Saturday, April 6, 13
21. (λx.2 * x + 1) 3 β-reduction abstraction application The are many application operators in Haskell, ML Saturday, April 6, 13
22. Q: “How it’s possible that everything is a transformation?” Saturday, April 6, 13
23. A: “Have you ever thought about how (4+5-2*9) works?” Saturday, April 6, 13
24. Programming language Hardware & compiler VS. Saturday, April 6, 13
25. What the problem is? “reusability” && “composability” ... oh, off course modularity matters, but we created many ways to split our programs since goto Saturday, April 6, 13
26. Imperative • hard to reuse/compose (context) • hard to test (context) • “interactive style” is hard • it’s not the language that I want to talk • parallelism is impossible • ... but it’s widespread • ... but it’s common • ... but it’s hard to see the root of the problems (“Vietnam”) Saturday, April 6, 13
27. Imperative advantages(?) • algorithms O(*) - the same • low level optimization? - oh, not in Python • manual memory control? - oh, not in Python Saturday, April 6, 13
28. Turing machine Assembly Algol 60/8 Fortran С Python Pascal Type theory Set theory λ-notation λ-calculus λ-calculus as PL Logic combinators ML (family) Haskell OCaml AST-base Lisp (family) ABC SETL Speedcoding Saturday, April 6, 13
29. When somebody tells you that each language is sugar over Turing machine... do not believe Saturday, April 6, 13
30. Python • mostly imperative, but... • higher-ordered functions (*) • lambdas (*) • no for(i=0;i<10;i++) (**) • iterators (**) • map/filter/zip/itertools (**) • generators (**) • futures (concurrency, tulip) * ast/abt ** sequence-based semantic Saturday, April 6, 13
31. Move on to more practical questions * starting from easiest: looking for high-level patterns Saturday, April 6, 13
32. http://wrongsideofmemphis.files.wordpress.com/2013/03/screen-shot-2013-03-23-at-12-32-17.png Saturday, April 6, 13
33. Do you see the patterns? Saturday, April 6, 13
34. Do you see the patterns? Saturday, April 6, 13
35. Do you see the patterns? Saturday, April 6, 13
36. Do you see the patterns? Saturday, April 6, 13
37. Saturday, April 6, 13
38. Saturday, April 6, 13
39. Saturday, April 6, 13
40. Saturday, April 6, 13
41. Do you see the patterns? * we already talked that loops do not compose Saturday, April 6, 13
42. Do you see the patterns? Saturday, April 6, 13
43. Saturday, April 6, 13
44. Not only syntax... • transformations instead of instructions • reduction declarations without dealing with application • reuse pure function in some context (functor) • high(er) level of composability Saturday, April 6, 13
45. When syntax sucks... Saturday, April 6, 13
46. Iterators is not only about lists ... this is the semantic way to think about possible solutions Saturday, April 6, 13
47. Saturday, April 6, 13
48. Only last function matters ... other functions are common and you can find them in Python documentation or implemented in Fn.py library Saturday, April 6, 13
49. More examples Lazy evaluation and declarative approach: http://kachayev.github.com/talks/ Saturday, April 6, 13
50. What stuff do you know about? • iterators • generators • lazy-evaluation • undelimited continuations • delimited continuations • coroutines • macros • monads • “staging” • “deref scope” Saturday, April 6, 13
51. What stuff do you use in code? • iterators • generators • lazy-evaluation • undelimited continuations • delimited continuations • coroutines • macros • monads • “staging” • “deref scope” Saturday, April 6, 13
52. What stuff do you want to use? • iterators • generators • lazy-evaluation • undelimited continuations • delimited continuations • coroutines • macros • monads • “staging” • “deref scope” Saturday, April 6, 13
53. I saw many coroutines during conference talks Saturday, April 6, 13
54. I never saw coroutines in real-life projects Saturday, April 6, 13
55. Can you describe* coroutine advantages? * using one word Saturday, April 6, 13
56. Can you describe coroutine disadvantages? Saturday, April 6, 13
57. What the problem is? • easy to start with simplest stuff (it’s cool, but don’t stop!) • habits, traditions (???) • mutable variables and assignments dictate (*) • syntax doesn’t support non-imperative semantic (“for” is only one good example of support, “yield from” is also cool) (**) • internal contradictions (***) Saturday, April 6, 13
58. Can you see semantic under the syntax? Saturday, April 6, 13
59. https://gist.github.com/e000/1023982 Saturday, April 6, 13
60. Are you getting on a bit? Saturday, April 6, 13
61. Can you see ABT under your AST? Saturday, April 6, 13
62. I don’t want you to write code this way I just want you to understand how it works and why it’s possible Saturday, April 6, 13
63. BTW, it’s common pattern in JS code... Saturday, April 6, 13
64. yield from is not only the new syntax! Saturday, April 6, 13
65. Saturday, April 6, 13
66. Saturday, April 6, 13
67. It’s all about composition. Saturday, April 6, 13
68. You can (*) write point- free (**) code * you just don’t have readable syntax to do this ** applyTwice is good example to show Saturday, April 6, 13
69. Isn’t this wonderful? Saturday, April 6, 13
70. Contra • no composition syntax!!! • okay... def new function (not readable enough) • no recursion!!! • okay... the list is...? iterators is...? • oh, I know! recursion = fold + unfold :) • no fold!!! we have list comprehensions • but... LC = map&filter... okay... Saturday, April 6, 13
71. Code vs. Ideas So now reduce(). This is actually the one I've always hated most, ... almost every time I see a reduce() call with a non-trivial function argument, I need to grab pen and paper to diagram... it's better to write out the accumulation loop explicitly. (c) Guido Van Rossum Saturday, April 6, 13
72. fold / unfold ... dig deeper Saturday, April 6, 13
73. Everybody knows this examples... Saturday, April 6, 13
74. Dig deeper. Saturday, April 6, 13
75. Saturday, April 6, 13
76. I want you to think about semantic Saturday, April 6, 13
77. In 5 years Python will solve other problems Saturday, April 6, 13
78. In 5 years Python should (*) solve other problems * technologies are changing very fast Saturday, April 6, 13
79. Is Python ready to be a cutting-edge language? Saturday, April 6, 13
80. Are you ready? Saturday, April 6, 13
81. Questions? * other talks: https://kachayev.github.com/talks ** fn.py: https://github.com/kachayev/fn.py Saturday, April 6, 13