PicoML

A toy programming language which is a subset of OCaml.

let rec fact n = if n < 2 then 1 else n * fact(n - 1) in
let rec range s e = if s >= e then [] else s::(range (s + 1) e) in
let rec map f list = match list with [] -> [] | x::y -> (f x)::(map f y) in
map fact (range 1 7) (* ==> int list: [ 1, 2, 6, 24, 120, 720 ] *)

Features

• Interpreter
• Type inference
• Compile to WASM

Web Playground

You can try PicoML here.

How to use

Install

$ npm i -g pico-ml

REPL

You can REPL with ipml command.

$ ipml

# Input ML expression to evaluate
> let add = fun a -> fun b -> a + b in add 1 2;;

The REPL allows multiple line input. Enter ;; to evaluate the input expression.

Compiler

(* example.ml *)

let add = fun a -> fun b -> a + b in add 1 2

To compile Web Assembly module, use pmlc command.

$ pmlc example.ml

The generated module exports main function to evaluate the input expression.

// Execute in browser

const instance = await WebAssembly.instatiateStreaming(fetch("example.wasm"), {});
const result = instance.exports["main"]();
console.log(result);

// Execute in Node.js

const fs = require("fs/promises");

(async () => {
  const source = await fs.readFile("example.wasm");
  const { instance } = await WebAssembly.instantiate(source, {});
  const result = instance.exports["main"]();
  console.log(result);
})();

And pmlc can also outputs WAT file with -t option.

$ pmlc example.ml -t

Language

BNF

expr    ::= id |
            int |
            decimal |
            bool |
            "[]" |
            expr expr |
            unop expr |
            expr binop expr |
            expr "::" expr |
            "if" expr "then" expr "else" expr |
            "match" expr "with" clause |
            "fun" id "->" expr |
            "let" id id* "=" expr "in" expr |
            "let" "rec" id "=" "fun" id "->" expr "in" expr |
            "let" "rec" id id+ "=" expr "in" expr

clause  ::= pat "->" expr | pat "->" expr "|" clause

pat     ::= id | "[]" | "_" | pat "::" pat

id      ::= (letter | "_"){ letter | digit | "_" | "'" }

unop    ::= "-" | "-."

binop   ::= "+" | "-" | "*" | "/" | +." | "-." | "*." |"/." | "<" | ">" | "<=" | ">=" | "=" | "<>" | "==" | "!=" | "&&" | "||"

bool    ::= "true" | "false"

int     ::= (digit)+

decimal ::= digit+"."digit*

letter  ::= "a" | ... | "z" | "A" | ... | "Z"

digit   ::= "0" | ... | "9"

License

MIT