title: First GNU Guile Patch and More Guix Packages
date: 2013-11-22 21:00
tags: gnu, guix, scheme, guile, wsu
summary: I added alist->hash-table procedures for Guile’s native hash table implementation and packaged SDL libraries for Guix.
---

I have spent some of the last month working on contributing to GNU
Guile and now I can finally say that I have contributed code to the
project. Guile has several hash table implementations: a Guile native
one, SRFI-69, and R6RS. SRFI-69 contains a handy procedure,
`alist->hash-table`, which allows for a sort of hash literal-like
syntax:

```scheme
(alist->hash-table
 '((foo . 1)
   (bar . 2)
   (baz . 3)))
```

However, I prefer to use Guile’s native hash implementation, and
SRFI-69 is incompatible with it, so I decided to port
`alist->hash-table`. Unfortunately, it was not as simple as writing
just one procedure. The native hash tables actually have 4 different
ways of doing key comparisons: Using `equal?`, `eq?`, `eqv?`, and
user-defined procedures. This is a design flaw because the user must
make sure to use the right procedures at all times rather than simply
set the `hash` and `assoc` procedures when creating the hash table
instance.

Below is the final implementation. Since 3 of the 4 variations were
essentially the same, I wrote a short macro to reduce code
duplication.

```scheme
;;;; Copyright (C) 2013 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;;;

(define-syntax-rule (define-alist-converter name hash-set-proc)
  (define (name alist)
    "Convert ALIST into a hash table."
    (let ((table (make-hash-table)))
      (for-each (lambda (pair)
                  (hash-set-proc table (car pair) (cdr pair)))
                (reverse alist))
      table)))

(define-alist-converter alist->hash-table hash-set!)
(define-alist-converter alist->hashq-table hashq-set!)
(define-alist-converter alist->hashv-table hashv-set!)

(define (alist->hashx-table hash assoc alist)
  "Convert ALIST into a hash table with custom HASH and ASSOC
procedures."
  (let ((table (make-hash-table)))
    (for-each (lambda (pair)
                (hashx-set! hash assoc table (car pair) (cdr pair)))
              (reverse alist))
    table))
```

Not only did I manage to get my code into Guile, I was given commit
access to GNU Guix by the lead developer, Ludovic Courtès. I have
never had commit access to any free software project repositories
besides my own. I feel quite honored, as cheesy as that may sound.

Packages for SDL and SDL2 have been merged into master, and packages
for SDL_gfx, SDL_image, SDL_mixer, SDL_net, and SDL_ttf for SDL 1.2
are pending review.

I like to show off the elegance of Guix package recipes, so here’s
some code:

```scheme
;;; Copyright © 2013 David Thompson <dthompson2@worcester.edu>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define sdl
  (package
    (name "sdl")
    (version "1.2.15")
    (source (origin
             (method url-fetch)
             (uri
              (string-append "http://libsdl.org/release/SDL-"
                             version ".tar.gz"))
             (sha256
              (base32
               "005d993xcac8236fpvd1iawkz4wqjybkpn8dbwaliqz5jfkidlyn"))))
    (build-system gnu-build-system)
    (arguments '(#:tests? #f)) ; no check target
    (inputs `(("libx11" ,libx11)
              ("libxrandr" ,libxrandr)
              ("mesa" ,mesa)
              ("alsa-lib" ,alsa-lib)
              ("pkg-config" ,pkg-config)
              ("pulseaudio" ,pulseaudio)))
    (synopsis "Cross platform game development library")
    (description "Simple DirectMedia Layer is a cross-platform development
library designed to provide low level access to audio, keyboard, mouse,
joystick, and graphics hardware.")
    (home-page "http://libsdl.org/")
    (license lgpl2.1)))

(define sdl2
  (package (inherit sdl)
    (name "sdl2")
    (version "2.0.0")
    (source (origin
             (method url-fetch)
             (uri
              (string-append "http://libsdl.org/release/SDL2-"
                             version ".tar.gz"))
             (sha256
              (base32
               "0y3in99brki7vc2mb4c0w39v70mf4h341mblhh8nmq4h7lawhskg"))))
    (license bsd-3)))
```

Much help is needed to package the GNU system for Guix. If you are
interested in helping, please drop by `#guix` on freenode, we are
friendly. :)