🤔

🤔 (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.

Usage

Run REPL:

$ cargo run

Features

• 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

Examples

See prelude for more examples.

Recursion and pattern matching

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

FizzBuzz

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))

Algebraic data types

data Maybe a = Just a | Nothing

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

Lists

let rec sum xs =
    match xs with
    | Nil -> 0
    | Cons x xs -> x + sum xs

let s = sum [1, 2, 3, 4, 5]

TODO

• 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
• ...