minml

A programming language experiment, to explore the idea of a strong, statically-typed language, which does not require any explicit type annotations.

There is only a rudimentary scope-checker presently implemented, but the semantics are designed for simple ML-style HM, plus Polymorphic Variants, and Structural Types. Still undecided on many details of how this may work - e.g. how parametric polyphorism is inferred (I am interested in FreezeML's approach as it may provide some flexibility via syntax rather than explicit types).

The compiler supports a Javascript backend, and has been bootstrapped (e.g. the source code of the minml compiler is written in minml), but should be straightforward to re-implement for WASM if the type semantics have been formalized.

Tutorial

minml is syntactically from the SML/OCAML/Haskell/F# family, and supports simple let bindings, first-class functions, and a simple module/namespacing system, in a manner that should be familiar to functional programmers. It is white-space significant ala Haskell and F# #light syntax.

Variables are immutable and introduced via let

let x = 1

First-class functions simply use -> (no keyword), and traditional compound let/lambda shorthand syntax is supported.

let f = x -> x + 1
let g x y = (x + y) / 2

Basic primitive types (Int, Float, String, Bool), plus List (brackets) and Tuple (braces) types.

let animals = ["cat", "dog", "fox"]
let account = {"Liz's Account", 1234.56, true}

Polymorphic variants are constructed with Capitalized symbols, and are always single argument data constructors.

let animal2 = Cat "Garfield"
let animal1 = Dog "Odie"

let cons_list = Cons {1, Cons {2, Nil {}}}

Simple pattern matching is supported in all symbol binding positions.

let {x, y} = {1, 2}
let (Cat name) = Cat "Nermal"

.. but pattern matching is unified with function syntax using the | operator, like a match statement without the match keyword (though match! macro is a available in the default namespace).

let list_length =
    | Cons x -> 1 + list_length x
    | Nil {} -> 0

Code can be organized in logical, strucurally typed units with the module keyword, and imported from other files via use. They can also be nested!

module math =

    let add x y = x + y
    let div x y = x / y

let x = math.add 1 2

use map
let my_map = map.from_array [{"Key1", 1}, {"Key2", 2}]

Macros are just regular functions; modules are the smallest unit of code compiled incrementally, so any definition in a module can be used as a macro, as long as it is of type Statement -> Statement, the Polymorphic Variant data structure which represents minml's AST. Macros are invoked with !, and subsequent macro arguments are delimited with :.

Some other macros.

// `if!`
let is_it_four x =
    if! x == 4 then:
        sys.log "It's 4!"
    else:
        sys.log "It's not 4!"

// `match!`
let head x = match! x with:
    | Cons {x, xs} -> x
    | Nil -> sys.fail "Don't write unsafe functions!"

// `str.str!`
let msg x = str.str!
    "This is an interpolated string, for example " x 
    " is a variable and " (x + 4) " is four more than that!"

// `js!` 
js! "console.log(" (msg 4) ")"

// `array.matrix!`
let identity3 = array.matrix!
    1 0 0
    0 1 0
    0 0 1

// `call_later!`
call_later! sys.log "I am called second!"
sys.log "I am called first!"

The special macros quote! and unquote! can be used to create the AST datastructure inline, for easy macro definitions

let call_later f = quote! js! "setTimeout(() => " (unquote! f) ")"

The test module comes with a simple macro-based assertion suite which executes at compile time.

test.assert! list_length cons_list == 2
test.assert! head cons_list == 1 

IDE

This repo is also a VS Code plugin which enables minml syntax highlighting; it can either be installed as a standard plugin, or executed via the included launch.json.

Development

minml is bootstrapped, and requires a copy of a previous version of itself to compile itself; hence, minml is included in its own devDependencies. To build, just runt he yarn boot command (but remember to run it twice to check if the version you've just built can self-compile!)

Old Repo

This project re-uses a name from a different, Haskell-based toy language which varies considerably from present. I honestly just really liked the name and wanted to re-use it; the old repository has been moved to texodus/minml-old.