🤔 (pronounced "hmm") is a simplistic functional programming language inspired by OCaml and Haskell.

Disclaimer: this is a toy project and not intended for production use.

Run REPL:

$ cargo run

• Hindley-Milner type inference
• Fixed-point combinator fix
• Pattern matching
• Algebraic data types
• Lists and tuples
• First-class functions
• Tail call optimization
• Whitespace insensitive
• REPL

See prelude for more examples.

let rec fib n =
 match n with
 | 0 -> 0
 | 1 -> 1
 | n -> fib (n - 1) + fib (n - 2)

putStrLn is a built-in impure function that prints a string to stdout.

let fizzbuzz n =
 let fz = "Fizz"
 in let bz = "Buzz"
 in let fzbz = "FizzBuzz"
 in let fb n =
 match (n % 3, n % 5) with
 | (0, 0) -> putStrLn fzbz
 | (0, _) -> putStrLn fz
 | (_, 0) -> putStrLn bz
 | _ -> putStrLn (intToString n)
 in
 discard (map (fun n -> fb (n + 1)) (range n))

data Maybe a = Just a | Nothing
let map f xs =
 match xs with
 | Just x -> Just (f x)
 | Nothing -> Nothing

let rec sum xs =
 match xs with
 | Nil -> 0
 | Cons x xs -> x + sum xs
let s = sum [1, 2, 3, 4, 5]

• Standalone scripts
• Proper prelude
• Explicit type annotations
• let rec .. in .. syntax sugar
• match guards
• Mutually recursive functions (currently supported with explicit fix)
• Multi-argument lambdas
• let bindings with arguments
• Better error messages
• Prettier pretty-printer
• Exhaustiveness checking for pattern matching
• String interning for identifiers
• Compilation (native and/or to JS)
• Typeclasses
• ...