BODOL

This is my language experiment.

Preliminary goals which may or may not be possible to combine:

• Pure functional language.
• Homoiconic in the Lisp tradition.
• Built on the traditional Lisp primitives.
• Hindley-Milner flavoured type system.
• Currying function calls.
• Pattern matching.

This is a work in progress. Don't expect it to even run its own test suite.

Not Implemented Yet

The language, and the reference implementation (which, be warned, is just a dumb, slow interpreter), still misses these things:

• Type system.
• Macros.
• Module system.
• A decision on lazy vs strict evaluation.

Inspiration

Clojure is great, but sometimes I miss static typing. Haskell is great, but sometimes I miss Lisp's elegantly simple syntax. Shen is a splendid compromise, but I found myself wishing it came with Haskell's uncompromising purity and Standard ML's straightforward type system. BODOL is my attempt at crossbreeding the three, with Shen obviously the major influence.

A Taste of BODOL

Functional hello world:

(ƒ factorial
  0 → 1
  n → (* n (factorial (- n 1))))

(ƒ fibonacci
  0 → 0
  1 → 1
  n → (+ (fibonacci (- n 1)) (fibonacci (- n 2))))

More advanced pattern matching:

(ƒ map
   f () → ()
   f (head . tail) → (cons (f head) (map f tail)))

(= '(2 3 4) (map (λ a → (+ a 1)) '(1 2 3))))

Currying:

(ƒ triplet a b c → (list a b c))
(define one-and (triplet 1))
(define one-and-two-and (one-and 2))
(= '(1 2 3) (one-and-two-and 3))

Take a look at the theoretically comprehensive test suite for examples of all the currently defined language features.

Test Drive

The BODOL prototype interpreter is written in Clojure, so you'll need to install Leiningen in order to run it. Optionally, you may also want to install rlwrap for a better line editing experience. Once that's done, check out the BODOL repo, cd over there and type:

$ ./repl
BODOL version 0.0.0
You are in a maze of twisty little passages, all alike.
→→

What's with those non-ASCII characters?

If you're discouraged by the curious absence of λ, ƒ and → on your keyboard, you can substitute Clojure's fn and defn or Common Lisp's lambda and defun for λ and ƒ respectively, and -> for →.

I realise some people feel very strongly that using non-ASCII characters in a programming language syntax, even optionally, is reckless, irresponsible and heretical. BODOL is probably not a great fit for those people.

Emacs bindings

If you're using Emacs, I find it helps to bind ƒ, λ and → to M-f, M-l and M-- (Alt+F, Alt+L and Alt+Minus) respectively.

;; Keybindings for special symbols
(global-set-key (kbd "M-l") (lambda () (interactive) (insert "\u03bb"))) ;lambda
(global-set-key (kbd "M-f") (lambda () (interactive) (insert "\u0192"))) ;function
(global-set-key (kbd "M--") (lambda () (interactive) (insert "\u2192"))) ;right arrow

;; Launch the BODOL REPL in an inferior-lisp buffer
(defun bodol-repl ()
  (interactive)
  (run-lisp "<path to your BODOL repo>/repl"))

Vim bindings

Add this snippet to your .vimrc to enable the same keybindings for vim.

" Keybindings for λ and ƒ
:inoremap <A-l> <C-v>u3bb<Space>
:inoremap <A-f> <C-v>u192<Space>
:inoremap <A--> <C-v>u2192<Space>

Mac OS X keybindings

If you're using Mac OS X, you can enable these keybindings globally by adding the following snippet to ~/Library/KeyBindings/DefaultKeyBinding.dict.

{
"~f" = ("insertText:", "\U0192"); /* alt + f ~> florin */
"~l" = ("insertText:", "\U03BB"); /* alt + l ~> lambda */
"~-" = ("insertText:", "\U2192"); /* alt + - ~> right arrow */
}

License

Copyright 2013 Bodil Stokke

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0.

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.