A minimal, efficient and practical programming language that aims to rethink functional programming from the scratch, and make it right. Under the hoods, it is basically Haskell, except without historical mistakes, and with a modern, consistent design. On the surface, it aims to be more practical, and to look more like conventional languages. Kind is statically typed, and its types are so powerful that you can prove mathematical theorems on it. Compared to proof assistants, Kind has:
-
The smallest core. Check FormCore.js or Core.kind. Both are
< 1000-LOC
complete implementations! -
Novel type-level features. Check this article on super-inductive datatypes.
-
An accessible syntax that makes it less scary. Check SYNTAX.md.
-
A complete bootstrap: the language is implemented in itself. Check it here.
-
Efficient real-world compilers. Check http://old.kindelia.org/ for a list of apps. (WIP)
-
Choose a release. We'll use JavaScript here but ChezScheme is also available.
-
Install Kind using
npm
:
npm i -g kind-lang
- Save the file below as
Main.kind
:
Main: IO(Unit)
IO {
IO.print("Hello, world!")
}
- Type-check it:
kind Main
- Run it:
kind Main --run
- Have fun!
Kind has an universal compiler that targets several back-ends. Just find what you need on Kind, and compile it with kind Main --lang
. For example, to generate a QuickSort function in JavaScript, just type kind List.quicksort --js
. You may never write code in any other language! Available targets: --js
, --scm
. Several more will be available eventually.
Kind has an interconnected back-end that allows you to create rich, interactive applications without ever touching databases, TCP packets or messing with apis. Just add a file to base/App
and it will be available on http://old.kindelia.org/. You can fork entire applications - not just the front-end, but all of it, back-end, database, and networking - in seconds.
No, theorems are not scary things mathematicians do. For programmers, they're more like unit tests, except they can involve symbols, allowing you to cover infinitely many test cases. If you like unit tests, you'll love theorems. To learn more, check THEOREMS.md. You can also compile Kind programs and proofs to a minuscle core language with the --fmc
flag (example: kind Nat.add.assoc --fmc
). Try it!
(Soon.)
// A 'Hello, world!"
Main: IO(Unit)
IO {
IO.print("Hello, world!")
}
// Quicksort (using recursion)
quicksort(list: List<Nat>): List<Nat>
case list {
nil:
[]
cons:
fst = list.head
min = filter!((x) x <? list.head, list.tail)
max = filter!((x) x >=? list.head, list.tail)
quicksort(min) [fst] quicksort(max)
}
// List iteration (using folds)
some_text: String
List.foldl!!("",
(str, result)
str = String.to_upper(str)
str = String.reverse(str)
result | str,
["cba","fed","ihg"])
// List iteration (using fors)
some_text: String
result = ""
for str in ["cba","fed","ihg"] with result:
str = String.to_upper(str)
str = String.reverse(str)
result | str
result
// Map, Maybe, String and Nat sugars
sugars: Nat
key = "toe"
map = {"tic": 1, "tac": 2, key: 3} // Map.from_list!([{"tic",1}, ...])
map = map{"tic"} <- 100 // Map.set!("tic", 100, map)
map = map{"tac"} <- 200 // Map.set!("tac", 200, map)
map = map{ key } <- 300 // Map.set!(key, 300, map)
val0 = map{"tic"} <> 0 // Maybe.default!(Map.get!("tic",map), 0)
val1 = map{"tac"} <> 0 // Maybe.default!(Map.get!("tac",map), 0)
val2 = map{ key } <> 0 // Maybe.default!(Map.get!(key, map), 0)
val0 val1 val2 // Nat.add(val0, Nat.add(val1, val2))
// List monadic block: returns [{1,4},{1,5},{1,6},{2,4},...,{3,6}]
my_list: List<Pair<Nat,Nat>>
List {
get x = [1, 2, 3]
get y = [4, 5, 6]
return {x, y}
}
Check many List algorithms on base/List!
// A boolean
type Bool {
true
false
}
// A natural number
type Nat {
zero
succ(pred: Nat)
}
// A polymorphic list
type List <A: Type> {
nil
cons(head: A, tail: List<A>)
}
// A polymorphic pair
type Pair <A: Type, B: Type> {
new(fst: A, snd: B)
}
// A polymorphic dependent pair
type Sigma <A: Type, B: A -> Type> {
new(fst: A, snd: B(fst))
}
// A polymorphic list with a statically known size
type Vector <A: Type> ~ (size: Nat) {
nil ~ (size = 0)
cons(size: Nat, head: Nat, tail: Vector<A,size>) ~ (size = 1 size)
}
// A bounded natural number
type Fin ~ <lim: Nat> {
zero<N: Nat> ~ (lim = Nat.succ(N))
succ<N: Nat>(pred: Fin<N>) ~ (lim = Nat.succ(N))
}
// The type used in equality proofs
type Equal <A: Type, a: A> ~ (b: A) {
refl ~ (b = a)
}
// A burrito
type Monad <M: Type -> Type> {
new(
bind: <A: Type, B: Type> M<A> -> (A -> M<B>) -> M<B>
pure: <A: Type> A -> M<A>
)
}
// Some game entity
type Entity {
player(
name: String
pos: V3
health: Nat
items: List<Item>
sprite: Image
)
wall(
hitbox: Pair<V3, V3>
collision: Entity -> Entity
sprite: Image
)
}
Check all core types on base!
// Proof that `a == a 0`
Nat.add.zero(a: Nat): a == Nat.add(a, 0)
case a {
zero: refl
succ: apply(Nat.succ, Nat.add.zero(a.pred))
}!
// Proof that `1 (a b) == a (1 b)`
Nat.add.succ(a: Nat, b: Nat): Nat.succ(a b) == (a Nat.succ(b))
case a {
zero: refl
succ: apply(Nat.succ, Nat.add.succ(a.pred, b))
}!
// Proof that addition is commutative
Nat.add.comm(a: Nat, b: Nat): (a b) == (b a)
case a {
zero:
Nat.add.zero(b)
succ:
p0 = Nat.add.succ(b, a.pred)
p1 = Nat.add.comm(b, a.pred)
p0 :: rewrite X in Nat.succ(X) == _ with p1
}!
Check some Nat proofs on base/Nat/add!
// Render function
App.Hello.draw: App.Draw<App.Hello.State>
(state)
<div style={"border": "1px solid black"}>
<div style={"font-weight": "bold"}>"Hello, world!"</div>
<div>"Clicks: " | Nat.show(state@local)</div>
<div>"Visits: " | Nat.show(state@global)</div>
</div>
// Event handler
App.Hello.when: App.When<App.Hello.State>
(event, state)
case event {
init: IO {
App.watch!(App.room_zero)
App.new_post!(App.room_zero, App.empty_post)
}
mouse_down: IO {
App.set_local!(state@local 1)
}
} default App.pass!
Source: base/App/Hello.kind
Live: http://old.kindelia.org/App.Hello
In order to run this or any other app you should follow this steps:
- The app should be in
base/App
folder - Install necessary packages in web folder with
npm i --prefix web/
- Install
js-beautify
usingsudo npm i -g js-beautify
- Build the app you want with
node web/build [name of app]
(in this example would benode web/build Hello
) - Run a local server with
node web/server.js 8080
- Open http://localhost:8080 in your favorite browser and see your app working
There are so many things we want to do and improve. Would like to contribute? Check CONTRIBUTE.md. Also reach us on Telegram. We're friendly!