A functional language with invisible types, safe ownership, and algebraic effects.
Hindley-Milner inference eliminates type annotations. Ownership checking runs without lifetime syntax. Effects replace exceptions, async, and state.
curl -fsSL https://loonlang.com/install.sh | shEverything is an expression
No statements, no void returns. Every construct — if, match, let — produces a value. Square brackets replace parentheses for a clean, uniform syntax.
Guide: Basics →[let greeting
[if [> hour 17]
"Good evening"
"Hello"]]
[println greeting] ; "Good evening"Functions and pipes
First-class functions with implicit do blocks. Pipe chains thread data through transformations without nesting or temp variables.
Guide: Functions →[fn process [items]
[pipe items
[filter [fn [x] [> [get x :score 0] 0.5]]]
[map [fn [x] [update x :score [fn [s] [* s 2]]]]]
[sort-by [fn [x] [get x :score 0]]]]]Types without typing
Complete Hindley-Milner inference with let-polymorphism and row types for records. The compiler infers every type — you never write one.
Concepts: Invisible types →; The compiler infers:
; compose : (b -> c) -> (a -> b) -> (a -> c)
[fn compose [f g]
[fn [x] [f [g x]]]]
[let inc-dbl [compose [fn [n] [+ n 1]]
[fn [n] [* n 2]]]]
[inc-dbl 5] ; 11Ownership without lifetimes
Values move by default. The compiler tracks ownership through dataflow analysis and catches use-after-move, double-free, and aliasing errors — no annotations needed.
Concepts: Ownership →[let items #[1 2 3]]
[let sorted [sort items]]
; items has moved — using it here
; is a compile error:
; [println items] ; error: moved
[println sorted] ; #[1 2 3]Algebraic effects
Declare effects as interfaces, perform them in functions, handle them at call sites. Effects replace exceptions, async/await, and mutable state with a single composable mechanism.
Concepts: Effects →[effect Ask
[prompt [q]]]
[fn greet []
[let name [Ask.prompt "Name?"]]
[str "Hello, " name "!"]]
; The caller decides how to handle it
[handle [greet]
[Ask.prompt q] [resume "World"]] ; "Hello, World!"Pattern matching
Match on literals, ADT constructors, and wildcards. Destructure values directly in let bindings, function parameters, and match arms.
Guide: Pattern matching →[type Shape
[Circle Float]
[Rect Float Float]]
[fn area [s]
[match s
[Circle r] [* 3.14 r r]
[Rect w h] [* w h]]]
[area [Circle 5.0]] ; 78.5