ADTs - Algebraic Data Types
Marius Jurgelenas
YGLF@Vilnius 2019
Corvid by Wix
What is the meaning of life types?
- Type inference?
- Static type checking?
- Autocomplete suggestions?
- Catching bugs?
Guess the type
Guess the type
Guess the type
Our brain is very good at inferring types
type OS = Linux or Windows or MacOS
type WorkPlace = Computer and Desk and Chair
type Computer = Hardware and OS
type Furniture = Desk or Chair
Composing types
Logic operations
AND
OR
Fruit Salad
type Fruit Salad = Apple AND Banana AND Cherry
How many different fruit salads can we make?
3 × 2 × 2 = 12
Product
Fruit Salad - a Product type
{
name: 'John', // string
age: 42, // number
ownsDog: true // boolean
}
Person - a Product type
type Fruit Snack = Apple OR Banana OR Cherry
Fruit Snack
How many different snacks can we have?
3 + 2 + 2 = 7
Sum
Fruit Snack - a Sum type
Algebraic Data Types
Product types
Sum types
langauge-agnostic
Are Sum types ok?
type snack = OR OR
type strangeThing = number OR boolean
const name = "Peter"
Guess the type
Uncought TypeError: Cannot read property 'toUpperCase' of undefined
name.toUpperCase()
if (name) {
return name.toUpperCase()
} else {
return "No name!"
}
Matching Types
type name = string OR undefined
The building blocks
- String
- Number
- Boolean
- Undefined/Null
Thinking in types makes the code better*
* - there is no scientific evidence to proove it
