What's in a language? How can it help us express our intent better? Based on his last talk, Cheng will explore some concrete, daily patterns in our codebase that Reason elegantly solves through a few simple yet rich concepts.

1. (Taming the Meta-Language, Part 2)
First-Class File

2. A long long time ago...

3. A long long time ago...
// this prints 5 times
print(1)
print(2)
print(3)
print(4)
print(5)

4. A long long time ago...
// this prints 11 times
print(1)
print(2)
print(3)
print(4)
print(5)
print(6)
print(7)
print(8)
print(9)
print(10)
print(11)

5. A long long time ago...
// @pragma 2-10
print(2)
print(3)
print(4)
print(5)
print(6)
print(7)
print(8)
print(9)
print(10)
// @end pragma 2-10

6. A long long time ago...
print(1)

7. A long long time ago...
for (i from 2 to 20) {
print(i)
}

8. Motivation
• Meta language, part 2 (concrete)
• Single Reason/OCaml feature

9. github.com/facebook/reason
github.com/reasonml/reason-react
discord.gg/reasonml

10. Ladder
• data
• function
• ...? React Component?
• ...??

11. require('myLibrary/myFile')

12. Ladder
• data
• function
• ...? React Component?
• ...??
• ...???

13. Module

14. Module

15. Module

16. • Module
• Module type
• Module function

17. type profession = ... /* type */
let person1 = ... /* binding */
let getProfession person => ... /* function */

18. type profession = ...
let person1 = ...
let getProfession person => ...

19. module School = { /* <-- module */
type profession = ...
let person1 = ...
let getProfession person => ...
};

20. module School = { /* <-- module */
type profession = ...
let person1 = ...
let getProfession person => ...
module GPA = {...} /* <-- nested module */
};

21. module School = { /* <-- module */
type profession = ...
let person1 = ...
let getProfession person => ...
module GPA = {...} /* <-- nested module */
};
let anotherPerson: School.profession = ...

22. module BaseComponent = {
let greeting = "Hello from base component";
let count = 10;
};
module ActualComponent = {
include BaseComponent; /* <-- JS object spread! */
let greeting = "Hello from actual component";
};

23. // Generated by BUCKLESCRIPT VERSION 1.2.1,
// PLEASE EDIT WITH CARE
var BaseComponent = /* module */[
/* greeting */"Hello from base component",
/* count */10
];
var ActualComponent = /* module */[
/* count */10,
/* greeting */"Hello from actual component"
];
module BaseComponent = {
let greeting = "Hello from base component";
let count = 10;
};
module ActualComponent = {
include BaseComponent; /* <-- JS object spread! */
let greeting = "Hello from actual component";
};

24. What Did We Push Down?
• Disciplined "mixins"

25. What Did We Push Down?
• Disciplined "mixins"
module BaseComponent = {
let greeting = "Hello from base component";
let count = 10;
};
module ActualComponent = {
include BaseComponent; /* <-- JS object spread! */
let greeting = "Hello from actual component";
};

26. What Did We Push Down?
• Disciplined "mixins"
module BaseComponent = {
let greeting = "Hello from base component";
let count = 10;
};
module ActualComponent = {
include BaseComponent; /* <-- JS object spread! */
let greeting = "Hello from actual component";
};

27. Surprise!

28. Every File Is a Module

29. Every File Is a Module
type profession = ... /* type */
let person1 = ... /* binding */
let getProfession person => ... /* function */

30. Every File Is a Module
module School = {
type profession = ...
let person1 = ...
let getProfession person => ...
};

31. Every File Is a Module
/* school.re */
module School = {
type profession = ...
let person1 = ...
let getProfession person => ...
};

32. Every File Is a Module
/* school.re */
type profession = ...
let person1 = ...
let getProfession person => ...

33. Every File Is a Module
/* school.re */
type profession = ...
let person1 = ...
let getProfession person => ...
/* agenda.re */
let p = School.person 1;

34. Every File Is a Module
/* school.re */
type profession = ...
let person1 = ...
let getProfession person => ...
module GPA = {...} /* <-- nested module */
/* agenda.re */
let p = School.person 1;

35. Every File Is a Module
/* school.re */
module GPA = {...};
module Records = {...};
module Rooms = {...};

36. Every File Is a Module
/* a.re */
let a = 1;
let b = 2;
let c = 3;
/* b.re */
include A;

37. What Did We Push Down?
• Code generation

38. Module Type (Signature)

39. Module Type (Signature)
module School = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};

40. Module Type (Signature)
module School = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};

41. Module Type (Signature)
module School = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};

42. Module Type (Signature)
module School = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};

43. Module Type (Signature)
module School = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};

44. module School = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};

45. module School = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};
{
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

46. module School: SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};
module type SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

47. • Module (Foo) -> normal file (foo.re)
• Module type (Foo) -> ???

48. • Module (Foo) -> normal file (foo.re)
• Module type (Foo) -> interface file (foo.rei)

49. What Did We Push Down?
• formalized documentation

55. module School: SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};
module type SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

56. module School: SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};
module type SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
/* let sortPeopleAlphabetically: people => people; */
};

57. module School: SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people = ["Mary", "John", "joe"];
let addPerson (p: person) (database: people) => [p, ...database];
let sortPeopleAlphabetically (database: people) => ...
};
module type SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
/* let sortPeopleAlphabetically: people => people; */
};

58. Last Trick: abstract type

59. Last Trick: abstract type
• "Lots of languages have facilities for encapsulation, but not
abstraction"

60. Last Trick: abstract type
module type SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

61. Last Trick: abstract type
module type SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
/* let sortPeopleAlphabetically: people => people; */
};

62. Last Trick: abstract type
module type SchoolType = {
type person = string;
type people = list person;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

63. Last Trick: abstract type
module type SchoolType = {
type person /* = string */;
type people /* = list person */;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

64. Last Trick: abstract type
module type SchoolType = {
type person;
type people;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

65. Last Trick: abstract type
module type SchoolType = {
type person;
type people;
let peopleDatabase: people;
let addPerson: person => people => people;
let sortPeopleAlphabetically: people => people;
};

68. What Did We Push Down?
• Encapsulation: The implementation details stay implementation
details
React.__SECRET_DOM_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
• Abstraction: nuance of breaking change migration paths

69. What Did We Push Down?
• Encapsulation: The implementation details stay implementation
details
React.__SECRET_DOM_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
• Abstraction: nuance of breaking change migration paths

70. Module Function (Functor)

71. Where Are We Going?

72. github.com/facebook/reason
github.com/reasonml/reason-react
discord.gg/reasonml