llrl: Lisp-like programming language powered by Rust + LLVM

llrl is an experimental Lisp-like programming language powered by Rust and LLVM.

Implementation notes (Japanese)

Features

llrl is not a highly carefully designed programming language, but it mainly borrows its design from OCaml, Rust, Haskell, and Scheme.

Self-hosting compiler implementation
Statically-typed
- Hindley-Milner based type system
- Supports type classes
Lisp-like syntax + macros
- Uses S-expressions to write programs
- Macros are compiled and executed by LLVM JIT
Modules
Closures
Algebraic data types
Pattern matching
...

Goals and Non-goals

llrl was originally started by learning LLVM Kaleidoscope Tutorial in Rust. This tutorial is great for learning LLVM frontend basics, but as the tutorial conclusion suggests, there are a lot of things to do to make our compiler more practical.

The goal of llrl is not to create a modern, practical programming language. Instead, llrl focuses to make a compiler self-hosted. To achieve this with LLVM-C API, we need to implement more language features like strings, pointers, etc. On the other hand, Implementing self-hosting compiler does not require a rich runtime system including garbage collections, exception handling, etc.

This goal has been achieved and can be tested by make self-hosting in llrl1/.

Roadmap

Usage

Since llrl0 is a standalone executable, you can simply run it with cargo run or cargo build.

cargo install --path llrl0
llrl0 --help
llrl0 -O examples/fibonacci-numbers

# or

cargo run -- -O examples/fibonacci-numbers

Requirements

Linux x64
- llrl does not take into account support for other platforms
glibc
- Not tested other C libraries but llrl depends a few implementation-details of glibc (plase see rt/rt.c)
clang
LLVM 11.0
- I use llvmenv for building LLVM
Boehm GC 8.0
- On Arch Linux, you can install Boehm GC by simply running pacman -S gc

Editor support

VSCode language support is available at yubrot/llrl-vscode.

Language Overview

Packages and Modules

Modules are identified by a string in the form of a path separated by a slash /. The first part of the path points to the name of the package, and the rest of the parts correspond to the file path on the package. If the file path on the package is omitted, it is treated as equivalent to <package-name>/prelude.

There are several predefined package names:

~: The special pakcage name that refers to the current package.
builtin: a set of language built-in definitions used directly by numeric literals, etc.
std: the llrl language standard library. std/prelude is implicitly imported in all modules (this behavior can be disabled with (no-implicit-std) declaration)

(import "std/hash-map" HashMap)

; Import all matching definitions by using `_` as a prefix or postfix
(import "std/hash-map" HashMap hash-map/_)

; Import everything
(import "std/hash-map" _)

; Export works as well
(export HashMap)

Functions

(function pi
  3.1415)

(function (square x)
  (* x x))

(function (squared-length a b)
  (+ (* a a) (* b b)))

pi                   ; => 3.1415
(square 10)          ; => 100
(squared-length 3 4) ; => 25

; With type signatures
(function pi {F64}
  3.1415)

(function (square x) {(-> I32 I32)}
  (* x x))

; Generalization
(function (identity x) {(forall A) (-> A A)}
  x)

; Generalization with constraints
(function (generic-square x) {(forall A) (-> A A) (where (Mul A))}
  (* x x))

Types

Primitive types are defined in builtin.llrl.

unit      ; Synonym for empty tuple (:)
Bool
I8
I16
I32
I64
U8
U16
U32
U64
F32
F64
String
Char

; Tuples
(: I32 I32)
(: String Char I32)

; Functions
(-> I32)
(-> I32 I32 I32)

; Option/Result
(Option I32)
(Result (Option I32) String)

Expressions

llrl does not have a main function, and the expressions written at the top level are executed in order.

; Literals
123
3.14
"Hello, World!\n"
#\a
#t
#f

; Function/macro application
(sqrt 2)
(+ 12 (* 34 56) 78)

; Conditional branching
(if #f
  (println! "then")
  (println! "else))

; Sequencing
(begin
  (println! "a")
  (println! "b")
  (println! "c"))

; Local variable binding
(let ([a 12]
      [b 34])
  (+ a b))

; Local function binding
(let ([(square x) (* x x)])
  (square 3))

; Loop
(let1 i (ref 0)
  (while (< ~i 5)
    (println! "Hello")
    (set! i (+ ~i 1))))

; Tuple creation
(: 12 "hello" #\x)

; Early return
(when (< x y) (return))

std/control contains general purpose macros that may be frequently used in expressions.

Data types

(data Answer
  answer:yes
  answer:no)

; Construction
answer:yes
answer:no

; Deconstruction
(match ans
  [answer:yes "yes"]
  [answer:no "no"])

; Constructors can have fields
(data Vec2
  (vec2: F32 F32))

(function (vec2/new x y)
  (vec2: x y))

(function (vec2/squared-length vec) {(-> Vec2 F32)}
  (match vec
    [(vec2: (let x) (let y))
      (+ (* x x) (* y y))]))

; Data types can be parameterized
(data (MyOption A)
  myopt:none
  (myopt:some A))

(function (myopt/or a b) ; inferred as {(forall A) (-> (MyOption A) (MyOption A) (MyOption A))}
  (match a
    [(myopt:some (let x))
      (myopt:some x)]
    [myopt:none
      b]))

builtin contains Option and Result declaration. These types are re-exported by std/option and std/result with utility functions and common type class instances.

Type classes

llrl type classes are almost same as Haskell 2010 type classes + MultiParamTypeClasses + FlexibleContexts FlexibleInstances + UndecidableInstances. Orphan checks, fundeps, and associated types are not implemented.

(class (Semigroup A)
  (function (<> x y) {(-> A A A)}))

Each class instance has its own name. Instances are automatically resolved when using methods of classes, but instances that are resolved automatically must exist in the current scope by import/export.

(instance Semigroup.I32 (Semigroup I32)
  (function (<> x y)
    (+ x y)))

(instance Semigroup.String (Semigroup String)
  (function (<> x y)
    (string x y)))

(println! (<> 12 34))
(println! (<> "foo" "bar"))

std provides several type classes that express frequently appearing operations like Eq, Ord, Display, etc.

std also supports automatic derivation of frequently used instances via derive macro.

(derive (Default Eq Ord DebugDisplay Hash)
  value-data (Vec2 A)
    (vec2: A A))

Macros

The definition of macros have the same form as functions, but the types of macros are always (-> (Syntax Sexp) (Result (Syntax Sexp) String)). (Syntax A) is the internal representation type used for embedding context information, and Sexp is the structure of S-expressions itself. This means that macros take the S-expression of the macro application (with context information) as an argument and either return the result of the macro expansion or return an expansion error. Since it is hard to deconstruct and construct S-expressions manually, there is s/match to deconstruct S-expressions and quoting to construct S-expressions.

For example, lambda syntax is defined as a macro in std/boot/5-lambda:

; Example use: (lambda (x y) (+ x y))
(macro (lambda s)
  (s/match s                                ; Matching with (lambda (x y) (+ x y))
    [(_ ,args ,@body)                       ; args := (x y), body := ((+ x y))
      (ok
        (let ([tmp-f (gensym)])             ; Generate a non-overlapping symbol
          `(let ([(,tmp-f ,@args) ,@body])  ; Construct a S-expression:
            ,tmp-f)))]                      ; (let ([(<tmp-f> x y) (+ x y)]) <tmp-f>)
    [_
      (err "Expected (lambda (arg ...) body ...)")]))

s/match and quasiquote are defined as macros in std/boot/2-s-match, std/boot/3-quasiquote.

'(quote), ` (quasiquote), , (unquote), ,@ (unquote-splicing) work just like any other Lisp, but there is a llrl-specific quoting, \ (capture). This captures the "use" of the definition in the scope. For example, and macro (defined in std/bool) uses the function && in the result of the macro expansion. Thanks to the capture, this points to the intended && even if && does not exist in the scope of the macro caller.

(macro (and s)
  (s/match s
    [(_)
      (ok '#t)]
    [(_ ,a ,@bs)
      (s/foldr (lambda (a b) `(,\&& ,a ,b)) a bs)]
    [_
      (err "Expected (and cond ...)")]))

To simplify the compilation and the JIT execution order, macros are not usable in the defined module.

llrl does not support hygienic macros.

Standard library

Many functionalities are implemented and provided in the standard library.

TODO: std overview?

chin0 / llrl