LunarML

A Standard ML compiler that produces Lua/JavaScript.

Building

You need a recent version of MLton to build the executable, and Lua 5.3+ or recent Node.js to run the compiled script.

$ make
$ make test
$ make test-lua-continuations
$ make test-luajit
$ make test-nodejs
$ make test-nodejs-cps
$ bin/lunarml compile example/hello.sml
$ lua example/hello.lua
Hello world!

Usage

lunarml [subcommand] [options] input.(sml|mlb)

Subcommand:

• compile: Compile a program.
• help: Show help.
• version: Show version information.

Targets:

• Lua
  • --lua (default): Targets Lua 5.3+.
  • --lua-continuations: Targets Lua 5.3+. Supports one-shot delimited continuations. Also, supports deeply nested handle.
  • --luajit: Targets LuaJIT.
• JavaScript (ES2020+)
  • --js: Produces a JavaScript program.
  • --js-cps: Produces a JavaScript program (CPS mode; supports delimited continuations).

Output type:

• --exe (default): Produces Lua/JavaScript program.
• --lib: Produces a Lua module.

Features

• Most of SML '97 language, including signatures and functors
• A subset of SML Basis Library
• Interface to Lua
• Interface to JavaScript
• Delimited continuations (experimental)
• ML Basis system like MLton

Successor ML features:

• Monomorphic non-exhaustive bindings
• Simplified recursive value bindings
  • SML '97-compatible ordering for type variables is also supported: val <tyvarseq> rec <valbind>
• Abstype as derived form
• Fixed manifest type specifications
• Abolish sequenced type realizations
• Line comments
• Extended literal syntax
  • Underscores (e.g. 3.1415_9265, 0xffff_ffff)
  • Binary notation (0b, 0wb)
  • Eight hex digits in text (\Uxxxxxxxx)
• Record punning
• Record extension
• Record update
• Conjunctive patterns
• Disjunctive patterns
• Nested matches
• Pattern guards
• Optional bars and semicolons
• Optional else branch
• Do declarations
• Withtype in signatures

Other extensions planned:

• Vector expressions and patterns
• Packaged modules (like in Alice ML or HaMLet S)
• Hexadecimal floating-point constants (e.g. 0x1p1024, 0x1.ffff_ffff_ffff_f)
• Variably-encoded Unicode escape sequence in string literals (e.g. \u{3042})
• Unicode identifiers

The syntax of hexadecimal floating-point constants is:

<hexadecimal-integer-constant> ::= '~'? '0' 'w'? 'x' <hexadecimal-digit-sequence>
<hexadecimal-floating-point-constant> ::= '~'? '0x' <hexadecimal-digit-sequence> (<binary-exponent-part> | '.' <hexadecimal-digit-sequence> <binary-exponent-part>?)
<hexadecimal-digit-sequence> ::= <hexadecimal-digit> ('_'* <hexadecimal-digit>)*
<binary-exponent-part> ::= [pP] '~'? <digit> ('_'* <digit>)?

In short: the (binary) exponent part is optional and use tilde (~) for the negation symbol.

The \u{} escape sequence allows you to embed a Unicode scalar value in a string literal. The compiler encodes the character in UTF-(8|16|32), depending on the string type.