SOSML: The Online Interpreter for Standard ML

SOSML is the online interpreter for the functional programming language Standard ML (SML), written in TypeScript. SOSML is used in a freshman class at Saarland University; you can check it out at https://sosml.org.

Features

Correctly lexing, parsing, elaborating and interpreting any SML core language program, i.e. a program that may contain the following constructs:

• Supported declarations (partially supported declarations in italics)
  • [x] value declarations (val x = 42;)
  • [x] function declarations (fun f 0 = 42 | f x = f (x-1);)
  • [x] type alias declarations (type t = 'a -> (int * int))
  • [x] datatype declarations (datatype tree = T of tree list;)
    • withtype will not be supported.
  • [x] abstract datatype declarations (abstype tree = T of tree list with val empty = T [];) Note that abstype is implemented as a derived form as proposed by Successor ML.
    • withtype will not be supported.
  • [x] exception declarations (exception E of int;)
  • [x] local declarations (local val x = 42; in val y = x + 2; end;)
  • [x] declaring operators as infix, nonfix, left, and right associative via infix, infixr, and nonfix
  • [x] open declarations
  • [x] structure declarations (structure S = struct end;)
  • [x] signature declarations (signature S = sig end;)
  • [x] functor declarations (experimental, functor F = struct end;)
• Supported expressions (This list is non-exhaustive)
  • [x] tuple ((1, 2, 3)), records ({a = 1, b = 2}), and lists ([1, 2, 3])
  • [x] application expressions (f x)
  • [x] infix expressions (3 + 4 - 5 * 6)
  • [x] andalso and orelse expressions
  • [x] raise and handle expressions
  • [x] conditionals (if true then 2 else 3)
  • [x] case analyses (case x of 0 => 0 | _ => 1)
  • [x] abstractions (fn 0 => 0 | _ => 1)
  • [x] while loops
  • [x] print
  • [x] ref, !, and :=
  • [x] structures
  • [x] signatures
  • [x] functors (experimental)
• Supported standard library constructs (Note that all available libraries are loaded per default, currently SOSML has not implemented any user-space loading of modules.)
  • Math library
  • Char library ord, chr, Char.isLower, Char.isUpper, Char.isDigit, Char.isAlpha
  • Int library Int.minInt, Int.maxInt, and Int.compare
  • Real library Real.compare, Real.fromInt, Real.round, Real.floor, and Real.ceil
  • Option library
  • List and Listsort libraries
  • Vector library fromList, tabulate, length, sub, update, app, map, foldl, foldr
  • Array library fromList, tabulate, length, sub, update, vector, foldl, foldr
  • String library

Using SOSML as an Interpreter for Standard ML (SML)

If you just want to test SOSML, just head to https://sosml.org/editor and enter your code. Adding a ; will then start the evaluation.

If you don't like web browsers, but still want to test SOSML, you can install the experimental CLI via npm

npm install -g @sosml/[email protected]

This makes the command sosml available, which behaves like any other run-of-the-mill interpreter for SML. Note that due to its experimental state, the CLI currently does not take any options or parameters.

Using SOSML as a Component in Your Project

The node Way

You may use the interpreter bundled in SOSML or parts of it to build your own fancy SML interpreter: First, install SOSML via

npm install --save @sosml/[email protected]

Now, to get your SML code interpreted by SOSML, import interpret and getFirstState from the package you just installed and you are good to go:

import { interpret, getFirstState, State } from '@sosml/interpreter';

// Obtain an initial state for the interpretation
let initialState: State = getFirstState();

// Let's interpret some code
let interpretationResult = interpret('val x = "Hello World!";', initialState);
console.log(interpretationResult.state.toString({stopId: initialState.id + 1})); // Prints "val x = "Hello World!": string;"

// Let's interpret some more code; note how we use the state obtained from the last step
interpretationResult = interpret('fun f y = x | f 10 = "???";', interpretationResult.state);

// Note that the last code produced a warning:
console.log(interpretationResult.warnings); // Something like "Rules after "y" unused in pattern matching."

// Similarly, interpretationResult.evaluationErrored may contain an Error if the interpretation of your code failed
// Lastly, SML exceptions raised by your code that are not handled end up in interpretationResult.error.

Check out the src/cli.ts file for an example SML interpreter using SOSML.

The “But I Hate node.js” Way

Starting with version 1.5.0, you can directly run SOSML in a <script> tag in HTML:

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <script src="https://unpkg.com/@sosml/[email protected]^1.5.0/build/interpreter.min.js"></script>
    </head>
    <body>
        <script>
            let initialState = Interpreter.getFirstState();
            let interpretationResult = Interpreter.interpret('val x = "Hello World!";', initialState);
            console.log(interpretationResult.state.toString({stopId: initialState.id + 1}));
            interpretationResult = Interpreter.interpret('fun f y = x | f 10 = "???";', interpretationResult.state);
            console.log(interpretationResult.warnings);
        </script>
    </body>
</html>

Contributing to SOSML

We welcome you to open an Issue for any error or squid you may find, and we will try to fix it ASAP. Further, if you want additional parts of the Standard Library or other features in general implemented, feel free to open a new Issue.

If you want to contribute via writing code, you may check the Issues page for any unresolved problems or unimplemented features and then submit a pull request after solving that problem or implementing that feature.

Cloning and Building

To get started on writing code for SOSML, clone the repository and install the dependencies:

git clone https://github.com/SOSML/SOSML
npm install

To build the interpreter and pack it into one file using Webpack run:

npm run build

This will create a file in the directory build called interpreter.js.

To also minify the result run:

npm run dist

This will create a file in the directory build called interpreter.min.js.

To build the CLI, run

npm run cli
npm link

Testing Your Changes

SOSML comes with an extensive set of tests which can be run via

npm test

This runs all tests located in the test directory. When contributing new code, please make sure that you add the appropriate tests and that no old tests begin to fail.