Getting started with Clojure/Emacs/Slime May 4th, 2010
Patrick Stein

I spent some considerable time yesterday poring over the shelves in the programmer’s section of a local bookstore yesterday. Based on the available jobs at the moment, I was trying to decide whether it would be less painful to learn C#/.NET/AFW/blurpz or Hibernate/Springs/Struts/glorpka. My lambda, those things are fugly. When I open a book to find that my simple database example takes eight XML configuration files and twenty-five lines of calls to the same function (with a 25-character identifier (which, technically, should be namespace qualified, too)), I just don’t want to go there.

So, I walked away with Programming Clojure and a determination to think really hard about how to get paid to do something that’s not intensely painful.

Well, yesterday afternoon and late-night were intensely painful trying to get Clojure/Emacs/Slime all working together. Today, magickly, I messed something up in my .emacs file that convinced swank-clojure to download its own copies of the three JAR files it needs and zoom… I’m out of the gate.

Someday, I’d still like to be able to use my own JAR files for all of this, but in the meantime, I’m up and running.

Here’s what works

This is the relevant configuration from my .emacs file. It draws partly from these instructions by I’m not sure who, partly from this message by Constantine Vetoshev, partly from how my .emacs file was previously arranged, partly from sources now lost in the browser history sea, and partly from sheer luck.

First, some generic stuff up at the beginning:

(defun add-subdirs-to-load-path (dir)
  (let ((default-directory (concat dir "/")))
    (normal-top-level-add-subdirs-to-load-path)))

(add-to-list 'load-path "~/.emacs.d/site-lisp")
(add-subdirs-to-load-path "~/.emacs.d/site-lisp")

Then, prepping slime a bit:

(require 'slime-autoloads)
(add-to-list 'load-path "~/.emacs.d/site-lisp/slime/contrib")

(add-hook 'lisp-mode-hook (lambda () (slime-mode t)))
(add-hook 'inferior-lisp-mode-hook (lambda () (inferior-slime-mode t)))
(setq common-lisp-hyperspec-root
      "file:///Developer/Documentation/Lisp/clhs/HyperSpec/")

(slime-setup '(slime-repl))

(setq slime-net-coding-system 'utf-8-unix)

Then, setting up some general stuff for easy lisp implementations. (The –sbcl-nolineedit is something I personally use in my .sbclrc to decide whether to load linedit.)

(setq slime-lisp-implementations
      '((sbcl ("sbcl" "--sbcl-nolineedit"))
        (ccl ("ccl"))
        (ccl64 ("ccl64"))))

Some commands to simplify things so I don’t have to remember to M–– M-x slime:

(defmacro defslime-start (name mapping)
  `(defun ,name ()
     (interactive)
     (let ((slime-default-lisp ,mapping))
       (slime))))

(defslime-start ccl 'ccl)
(defslime-start ccl64 'ccl64)
(defslime-start clojure 'clojure)
(defslime-start sbcl 'sbcl)

Then, Clojure-specific SLIME stuff

(autoload 'clojure-mode "clojure-mode" "A major mode for Clojure" t)
(add-to-list 'auto-mode-alist '("\\.clj$" . clojure-mode))
(require 'swank-clojure)

(setq slime-lisp-implementations
      (append slime-lisp-implementations
              `((clojure ,(swank-clojure-cmd) :init swank-clojure-init))))

And, a touch more slime stuff to make things a little happier.

(add-hook 'slime-mode-hook
          (lambda ()
            (setq slime-truncate-lines nil)
            (slime-redirect-inferior-output)))

In my .emacs.d/site-lisp, I did the following:

% rm -rf slime swank-clojure clojure-mode
% git clone git://git.boinkor.net/slime.git
% git clone http://github.com/technomancy/swank-clojure.git
% git clone http://github.com/jochu/clojure-mode.git

What didn’t work

Before accidentally triggering swank-clojure to download its own JARs, I tried installing what I could with ELPA. I tried installing clojure, clojure-contrib, and swank-clojure with Lein. I tried installing them with Maven. I tried various combinations of versions of clojure and swank-clojure.

I have no idea how the JARs that swank-clojure built itself got built. I cannot reproduce it.

Edit: Ah, it appears that the Subversion repository for Clojure that I found is deprecated. But, I don’t have the energy to try the git repository myself at this point. Maybe next week.

Weblocks Slides April 26th, 2010
Patrick Stein

At the TC Lispers meeting tonight, I will be giving a little presentation about weblocks. Here are slides for that presentation.

ps. if you’re in range, come to the meeting… Common Roots Cafe in Minneapolis.

CL-Growl Slides April 23rd, 2010
Patrick Stein

On Monday, I am giving a lightning talk at the TC Lispers meeting about my Common Lisp Growl client library.

Here are the slides with presenter notes and the accompanying sample code.

C++ Clifford Algebra library getting some use… April 13th, 2010
Patrick Stein

The C++ template classes that I wrote years ago have been one of the most consistent draws to my my website. Every time I check the search terms that brought someone to my site, there are always a few hits for Clifford algebras.

I just received some email today from Mijail Guillemard at the University of Hamburg saying that he extended my Clifford algebra classes and is using them to do feature separation and classification for signal processing.

XML Parser Generator March 16th, 2010
Patrick Stein

A few years back (for a very generous few), we needed to parse a wide variety of XML strings. It was quite tedious to go from the XML to the native-language representations of the data (even from a DOM version). Furthermore, we needed to parse this XML both in Java and in C++.

I wrote (in Java) an XML parser generator that took an XML description of how you’d like the native-language data structures to look and where in the XML it could find the values for those data structures. The Java code-base for this was ugly, ugly, ugly. I tried several times to clean it up into something publishable. I tried to clean it up several times so that it could actually generate the parser it used to read the XML description file. Alas, the meta-ness, combined with the clunky Java code, kept me from completing the circle.

Fast forward to last week. Suddenly, I have a reason to parse a wide variety of XML strings in Objective C. I certainly didn’t want to pull out the Java parser generator and try to beat it into generating Objective C, too. That’s fortunate, too, because I cannot find any of the copies (in various states of repair) that once lurked in ~/src.

What’s a man to do? Write it in Lisp, of course.

Example

Here’s an example to show how it works. Let’s take some simple XML that lists food items on a menu:

<menu>
        <food name="Belgian Waffles" price="$5.95" calories="650">
                <description>two of our famous Belgian Waffles with plenty of real maple syrup</description>
        </food>
        <!-- ... more food entries, omitted here for brevity ... -->
</menu>

We craft an XML description of how to go from the XML into a native representation:

<parser_generator root="menu" from="/menu">
  <struct name="food item">
    <field type="string" name="name" from="@name" />
    <field type="string" name="price" from="@price" />
    <field type="string" name="description" from="/description/." />
    <field type="integer" name="calories" from="@calories" />
  </struct>

  <struct name="menu">
    <field name="menu items">
      <array>
        <array_element type="food item" from="/food" />
      </array>
    </field>
  </struct>
</parser_generator>

Now, you run the parser generator on the above input file:

% sh parser-generator.sh --language=lisp \
                           --types-package menu \
                           --reader-package menu-reader \
                           --file menu.xml

This generates two files for you: types.lisp and reader.lisp. This is what types.lisp looks like:

(defpackage :menu
  (:use :common-lisp)
  (:export #:food-item
             #:name
             #:price
             #:description
             #:calories
           #:menu
             #:menu-items))

(in-package :menu)

(defclass food-item ()
  ((name :initarg :name :type string)
   (price :initarg :price :type string)
   (description :initarg :description :type string)
   (calories :initarg :calories :type integer)))

(defclass menu ()
  ((menu-items :initarg :menu-items :type list :initform nil)))

I will not bore you with all of reader.lisp as it’s 134 lines of code you never had to write. The only part you need to worry about is the parse function which takes a stream for or pathname to the XML and returns an instance of the menu class. Here is a small snippet though:

;;; =================================================================
;;; food-item struct
;;; =================================================================
(defmethod data progn ((handler sax-handler) (item food-item) path value)
  (with-slots (name price description calories) item
    (case path
      (:|@name| (setf name value))
      (:|@price| (setf price value))
      (:|/description/.| (setf description value))
      (:|@calories| (setf calories (parse-integer value))))))

Where it’s at

I currently have the parser generator generating its own parser (five times fast). I still have a little bit more that I’d like to add to include assertions for things like the minimum number of elements in an array or the minimum value of an integer. I also have a few kinks to work out so that you can return some type other than an instance of a class for cases like this where the menu class just wraps one item.

My next step though is to get it generating Objective C parsers.

Somewhere in there, I’ll post this to a public git repository.

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