Functional Programming

Models

Applications are stored as a data structure that stores the state. Every time an event happens(a function is called), a new state is generated, based upon the event, and the current state.

State

In Elm, your code cannot change state, which means that you cannot modify variables, and there are no loops, only recursion.

Syntax

Type Annotations

--Value
pi : Float
pi = 3.14

--Function
minus : Int -> Int -> Int
minus x y = x-y

add : Int -> Int -> Int -> Int
add a b c = a+b+c

sin : Float -> Float

Higher Order Functions

flip : (a -> b -> c) -> b -> a -> c
flip f x y = f y x

g : Int -> Int -> Int
g = flip minus

Union Types

Union types represent more than one possible value.

type Bool
	= True
	| False

type Thing
	= A
	| B
	| C
	| D

type Maybe

The maybe type represents a value that may or may not be there.

type Maybe a
	= Just a
	| Nothing

List.head : List a -> Maybe a

type Result

The result type represents either a success of a failure.

type Result err value
	= Ok value
	| Err err

toInt : string -> Result String Int