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Coalton is an efficient, statically typed functional programming language that supercharges Common Lisp.

Coalton can be written in files:

(in-package #:coalton-user)

(coalton-toplevel
  (define-type Symbol
    (Symbol String))

  (define (symbol-name sym)
    (match sym
      ((Symbol s) s)))

  (define-instance (Eq Symbol)
    (define (== a b)
      (== (symbol-name a) (symbol-name b)))
    (define (/= a b)
      (not (== a b))))

  (define-type Expr
    "A symbolic expression of basic arithmetic."
    (EConst Integer)
    (EVar   Symbol)
    (E+     Expr Expr)
    (E*     Expr Expr))

  (declare diff (Symbol -> Expr -> Expr))
  (define (diff x f)
    "Compute the derivative of F with respect to X."
    (match f
      ((EConst _)   ; c' = 0
       (EConst 0))
      ((EVar s)     ; x' = 1
       (if (== s x) (EConst 1) (EConst 0)))
      ((E+ a b)     ; (a+b)' = a' + b'
       (E+ (diff x a) (diff x b)))
      ((E* a b)     ; (ab)' = a'b + ab'
       (E+ (E* (diff x a) b)
           (E* a          (diff x b))))))

 (declare dt (Expr -> Expr))
 (define dt
   "The time derivative operator."
   (diff (Symbol "t"))))

And at the REPL:

CL-USER> (in-package #:coalton-user)
COALTON-USER> (coalton (dt (E+ (EVar (Symbol "t"))
                               (EConst 1))))
#.(E+ #.(ECONST 1) #.(ECONST 0))

Coalton has not reached "1.0" yet. This means that, from time to time, you may have a substandard user experience. While we try to be ANSI-conforming, Coalton may only work on SBCL 2.1.x.

What's Here?

This repository contains the source code to the Coalton compiler, and the standard library.

It also contains a few example programs, such as:

• Some simple pedagogical programs,
• A JSON parser piggybacking on a native Common Lisp library.
• An implementation of Jones's Typing Haskell in Haskell, and
• An implementation of a simple Quil parser.

Lastly and importantly, we maintain a collection of documentation about Coalton in the docs directory, including a standard library reference guide.

Getting Started

Install: Clone this repository into a place your Lisp can see. (Coalton is not yet on Quicklisp.)

Use: Either run (ql:quickload :coalton), or add #:coalton to your ASD's :depends-on list.

Test: Run (asdf:test-system :coalton).

Learn: We recommend starting with the Intro to Coalton document, and then taking a peek in the examples directory. It may also be helpful to check out the introductory blog post.

Get Involved

Want to ask a question about Coalton, propose a feature, or share a cool program you wrote? Try posting in the GitHub Discussions page!

We welcome contributions of all forms, especially as we stabilize toward a 1.0 release. We would be grateful to receive:

• bug reports (filed as issues),
• bug fixes and typo corrections (filed as pull requests),
• small example programs, and
• user experience troubles.