thautwarm/ml-to-scheme

Allow using ML to teach courses that're usually given in LISPs

ml-to-scheme

A simple ML language, see grammar at https://github.com/thautwarm/ml-to-scheme/blob/master/yesml.rbnf .

Target racket.

In fact not very trivial due to the greatly reduced code, and more easy-to-write and powerful pattern matching.

Usage

After cloning this repo, how about installing dependencies and ml2scm executable in 10 seconds ?

You might have suffered a lot from npm or other slow package managers.

git clone https://github.com/thautwarm/ml-to-scheme &&
pip install rbnf-rts                                &&
python setup.py install

And the usage is easy,

ml2scm <xxx.ml> <xxx.rkt>
racket xxx.rkt

# `mlscm xxx.ml` will execute the file directly.

Grammar

Do

In top level, you can execute expressions via the do syntax.

do println 1

Let-Definition

In top level, you can define a variable in this way:

let x = 1
let add10 = fun x -> x `+` 10

Open

It'll get mapped to racket's require syntax.

open racket/match
open "./utils"

maps to

(require racket/match)
(require "./utils")

Block Expression

Concatenate a list of expressions, execute them in order and treat the last one as return.

let x = print 1;
        print 2;
        3

Let In Expression

let ... and ... in ... juxtaposes several independent local bindings, and return the expression held after the token in.

let rec ... and ... in makes this series of local bindings able to mutually reference each other.

let f = fun x ->
    let rec f = fun x -> g x
    and g = fun y -> y + 1
    in f 2

Bool Expression

true || false
a `equals?` b && c

If, Lambda, Match

If:

if cond then
    true_clause
else
    false_clause

Lambda:

fn x -> x
fn x -> x end
fun x -> x
fun x -> x end

When there're syntactic conflicts, feel free to use end to resolve.

Match:

match x with
| [3, 4.0, "str", :symbol, _] -> ...
| [hd#tl] -> ...
| pattern when predicate ->
| as-pattern -> dosomewith(as-pattern)
| pat1 & pat2 & pat3 -> ...
| pat1 | pat2 | pat3 -> ...

The precedence of & is higher than |.

Still, feel free to add an end in the end of a match expression, to resolve possible syntactic conflicts.

Application

Things are not curried in fact.

f 1 is a syntax sugar for f(1).

You can define functions in this way:

let f = fun x1 -> fun x2 -> ...

By this, you can then use the function in the currying way f 1 2 ....

List Expression

There's no Tuple, due to the target language is racket. Use lists as tuples will suffice you use cases.

Note that to construct a list with a head and a tail, you can use [hd1, hd2, hd3#tl] or cons(hd1, cons(hd2, cons(hd3, tl))).

Check test directory for more examples.