If Socrates met Linus Torvalds, what would they talk about? How much math should be bundled into a good programming language? Can compiler resolve an argument and prove, that someone is right? Trough semantics of code, that we write every day, when looking carefully, one can see foundations of logic and science, that has been build more than 2000 years ago. Why does it matter, and how can we leverage this enormous power to make our code safe and sound in languages with advanced type systems, like Typescript and Scala.

1. What can philosophy teach
us about programming
Mike Kotsur
Amsterdam | April 2-3,
2019

2. 👋 Mike Kotsur
• Father, blogger, climber, tech lead.
• https://github.com/mkotsur/
• Specialist degree in applied math;
• 10+ years coding;
• “Native” languages: PHP, Java, Javascript,Typescript, Scala.
• Work: Startups, Marktplaats/eBay, XebiaLabs, Elsevier.

3. Douglas R.
Hofstadter,
Gödel, Escher, Bach
James R. Newman,
The World of
Mathematics
Immanuel Kant,
Kritik der reinen
Vernunft

4. confidence

5. Alex Honold scaling El Capitan (914m) without safety rope

6. Program Project
Language Program
Knowledge Language
Standard way of thinking

7. Program Project
Language Program
Knowledge Language
Thinking from first principles
Painful Learning

9. Pythagoras (570 – 495 BC)
• Founder of Pythagoreanism;
• The first man to call himself a
philosopher ("lover of wisdom”);
• One of the earliest vegetarians.

11. Socrates (570 – 495 BC)
• Famous by Plato’s dialogues;
• One of the founders of Western
philosophy;
• Socratic method

12. - Teacher:What is happening to our global climate?
- Stan: It’s getting warmer.
- Teacher: How do you know it’s getting warmer? What evidence do
you have to support your answer?
- Stan: We have all of these record heat days.
- Teacher: How do you know this is true?
- Stan: Scientists are saying that
- Teacher: How would they know?
- Stan:They have special equipment.
Source: Intel Tech Program, Designing Effective Projects

13. Socratic method
• False ignorance
• Goading (provoking, often by questions)
• Exposing fundamental premises
• Showing contradictions

14. Aristotle (470 – 399 BC)
• Along with Plato, he is considered
the "Father of Western Philosophy”;
• Defined syllogisms and introduced
Aristotelian logic;

16. Syllogisms and term logic
- No reptiles have fur;
- All snakes are reptiles;
- Therefore, no snakes have fur.
- No R have F;
- All S are R;
- Therefore, no S have F.

17. P: No one is free who has not obtained the
empire of himself.
M: I started the site when I was 19. I
didn't know much about business back
then.
S: The unexamined life is not worth living
L: Talk is cheap. Show me the code.
A: Let’s use symbols! For instance:
Every C is B
Every C is A
So, some A is B
H: Program is a proof
Pythagoras M. Zuckerberg
L.Torwalds
H. CurryAristotle
Socrates

18. Hey, Haskell, tell me more.
What do you mean by a “program is a proof” ??? 🤔
A moment ago
Haskell is typing…

19. That language is an instrument of human
reason, and not merely a medium for the
expression of thought, is a truth
generally admitted.
George Boole (1815 - 1864)
It is unworthy of excellent men to lose
hours like slaves in the labour of
calculation which could safely be
relegated to anyone else if machines were
used.
Gottfried Wilhelm Leibniz (1646 - 1716)
Yo! Check out those dudes 👇
A moment ago

20. A moment ago

21. A moment ago

22. Impressive! So people don’t make those stupid logical
mistakes anymore? 😈
20 seconds ago
%They do, but we’ve learned a lot…
10 seconds ago

23. Argument validity
Impossible for the premises to be true and
the conclusion false at the same time
✤ Animals that fly can live in trees
✤ Cats can fly
✤ Therefore cats can live in trees

24. Argument soundness
Not only valid, but the premises
are actually true
✤ Animals that fly can live in trees
✤ Cats can not fly
✤ Therefore cats can not live in trees

25. After this, therefore because of this
(Post Hoc, Ergo Propter Hoc)
Right when I sneezed, the power went off.
I must’ve caused the outage.

26. Genetic Fallacy
✤ Ha! I’m not reading that book.
✤ It was published inTennessee, and we
know allTennessee folk are hillbillies and
rednecks!

27. Circular reasoning
You can’t get a job without experience, and
you can’t get experience without a job.

28. Argument from force
(Argumentum ad Baculum)
✤ You say there’s no way you can finish the
project next week?
✤ Bullshit! Find a way! Make it happen! Just
do it!
✤ This is a million dollar contract and we
need it done byTuesday.

29. Slippery slope

30. Yes, talk is cheap,
show me the code!
But what about
programming?

31. Curry-Howard
isomorphism
In order to prove any mathematical
theorem, all we have to do is construct a
certain type which reflects the nature of
that theorem, then find a value that has that
type.

32. Math Computer science
Proofs
Formulas
Programs
Types
A implies B
A and B
A or B
Function from A => B
Tuple of A and B
Union of A and B
falsity
truth
empty type
singleton type
Axiom
Soundness Theorem
Completeness Theorem
Incompleteness Theorem
System Primitive
Compiler
Debugger
Infinite loop

33. Math Computer science
Double negation First class callbacks
Friedman’s translation
Dynamic Exceptions
Cohen’s Forcing Global Variables
Dialectica Translation
Scoped goto’s (e.g. Python’s
yield)

34. So, we are using math to describe the world.What are
you using your software stuff for?
3 minutes ago
We kind of create a virtual world with our own
rules…
20 seconds ago
Wow, how far you have gone!
A moment ago

35. I bet your tools guarantee that errors like in those
arguments can never even happen in this new world.
A minute ago
I wish…
A moment ago

36. Paradigm Description
Imperative, Structured,
Procedural
Programs as statements that directly change
computed state (datafields). Also with procedure calls.
Functional
Treats computation as the evaluation of mathematical
functions avoiding state and mutable data
Event-driven
Control flow is determined mainly by events, such
as mouse clicks or interrupts including timer
Object-oriented
Treats datafields as objects manipulated through
predefined methods only
Declarative Defines program logic, but not detailed control flow
Automata-based
programming
Treats programs as a model of a finite state machine or
any other formal automata
PROGRAMMING PARADIGMS
Source:Wikipedia:Comparisonofprogrammingparadigms

37. Source: https://github.com/denysdovhan/wtfjs
[] == ![]; // -> true
true == []; // -> false
true == ![]; // -> false
false == []; // -> true
false == ![]; // -> true
NaN === NaN; // -> false
WTF JS

38. Source: https://github.com/denysdovhan/wtfjs
document.all instanceof Object; // -> true
typeof document.all; // -> 'undefined'
Number.MIN_VALUE > 0; // -> true
WTF JS

39. Source: https://github.com/satwikkansal/wtfpython
>>> a = "wtf"
>>> b = "wtf"
>>> a is b
True
>>> a = "wtf!"
>>> b = "wtf!"
>>> a is b
False
WTF Python

40. Source: https://github.com/satwikkansal/wtfpython
WTF Python
some_dict = {}
some_dict[5.5] = "Ruby"
some_dict[5.0] = "JavaScript"
some_dict[5] = "Python"
>>> some_dict[5.5]
"Ruby"
>>> some_dict[5.0]
"Python"
>>> some_dict[5]
"Python"

41. WTF JS 53
WTF Python 51
&

42. Uh…That hurts my ancient geek brain!
5 seconds ago
Why would people do this?

43. “When it gets hard, we build
more escape hatches and tell
users to be careful.”
Amal Ahmed,All The Languages Together.
Presented at Strange Loop 2018

44. “I made up the term object-
oriented, and I can tell you I
did not have C++ in mind.”
Alan Kay, has designed a few programming languages

45. difficult

46. different
difficult

47. A change of
perspective is
worth 80 IQ points
Alan Kay

48. All good counsel begins in the same way; a man should know
what he is advising about, or his counsel will all come to
nought. But people imagine that they know about the nature
of things, when they don't know about them, and, not having
come to an understanding at first because they think that
they know, they end, as might be expected, in
contradicting one another and themselves.
Just now
I would hang this into every meeting room on this
planet!
A moment ago

49. 6 traits of
math friendly
programming
language

50. #1
total functions

51. String => String

52. def toLowercase: String => String

53. def getUserById: String => String

54. // "3977e5a0-78..." -> "jay123"
// "ill-formatted" -> null | Exception
// "bc75ee93-bd..." -> null
def getUserById: String => String

55. // "3977e5a0-78..." -> “jay123"
// "ill-formatted" -> ~NOT POSSIBLE~
// "bc75ee93-bd..." -> null
def getUserById: UUID => Try[Option[User]]

56. #2
type safety

57. UUID => Try[Option[User]]

58. #3
no side effects

59. #3
no side effects*
*in 95% of your code

60. def setupSession(uuid: UUID): Unit

61. def makeSession(uuid: UUID): Try[Session]

62. #4
first class and
higher order
functions

63. // # 4.1 First class function
List(1, 2, 3).map(x => x * 2)
// List(2, 4, 6)

64. // # 4.2 Higher order functions
def plus(a: Int, b: Int): Int = a + b
def plus_(a: Int)(b: Int): Int = a + b
def plus5: Int => Int = plus_(5)
plus5(2) // = 7

65. #5
Parametric
polymorphism

66. // # 5.1 Parametric
polymorphism
def dropFirstString: List[String] => List[String]
def dropFirstInt: List[Int] => List[Int]

67. // # 5.1 Parametric
polymorphism
def dropFirst[S](items: List[S]) = items.tail

68. // # 5.1 Parametric
polymorphism
def min[S: Ordering](items: List[S]) = {
val ordering = implicitly[Ordering[S]]
items.min(ordering)
}

69. // # 5.1 Parametric
polymorphism
type Ordering[T] = scala.math.Ordering[T]

70. // # 5.1 Parametric
polymorphism
def min[S: Ordering](items: List[S]) = {
val ordering = implicitly[Ordering[S]]
items.min(ordering)
}

71. // # 5.1 Parametric
polymorphism
import cats.{Order, Reducible}
def min2[C[_]: Reducible, S: Order](items: C[S]) = {
val reducer = implicitly[Reducible[C]]
reducer.minimum(items)
}

72. // # 5.1 Parametric
polymorphism
import cats.implicits._
import cats.data._
min2(NonEmptyList.of(5, 2, 4)) // 2

73. #6
Type Inference

74. // Type inference
// Local variable
const x = 2 * 2 // number
// Best common type
const y = [0, 1, null]; // (number | null)[]
// Context based
window.onmousedown = mouseEvent => {
// mouseEvent: MouseEvent
console.log(mouseEvent.button);
};

75. • Math is the most precise and unambiguously language that describes
the world.
• It’s the most advanced and rich language as well.
• “Invest” in math friendly languages.
• For Math = Correctness.
• And that gives you confidence.

76. confidence
is
timeless

77. Inclusive and language-agnostic meetup
group for those who cares about
TypeSafety
~ welcomes new members and potential speakers ~
http://slack.typesafeutrecht.net
http://meetup.typesafeutrecht.net

78. Q&A

79. REFERENCES
• 1. «The Curry-Howard isomorphism for dummies» (INRIA Junior Seminar), 17/02/2015 https://
www.xn--pdrot-bsa.fr/publications.html
• 2. IntelTeach Program: Designing Effective Projects, https://www.intel.com/content/dam/www/program/
education/us/en/documents/project-design/strategies/dep-question-socratic.pdf
• 3.AllThe LanguagesTogether: https://thestrangeloop.com/2018/all-the-languages-together.html
• 4.Type Systems,Wikipedia: https://en.wikipedia.org/wiki/Type_system
• 5. How to implement type theory in an hour: http://math.andrej.com/2018/08/25/how-to-implement-
type-theory-in-an-hour/
• 6. Comparison of programming paradigms,Wikipedia: https://en.wikipedia.org/wiki/
Comparison_of_programming_paradigms