Literate WordPress May 6th, 2010
Patrick Stein

I use WordPress along with the CodeColor plugin. This works fairly well for me. I find myself, however, breaking code up into sometimes awkward chunks to describe the code here or leaving things in very long segments.

Further, I often leave them ordered in my post in an order where they would compile if you just copied them into a file in the order presented. That’s not always the most useful order to present the code.

Literate programming seeks to tackle exactly these problems. So, I got to thinking: Why don’t I write some filters for noweb to output into WordPress+CodeColorer.

My Solution

My solution is in two parts, one filter of general use to all noweb users which simply inserts @language tags into the noweb stream and a noweave backend that outputs something you can just paste into the WordPress (HTML) input box.

Here is an example of how I used this to process the post.nw file that I used to compose this post. 

# example.sh
noweave -n -filter langify-nw -backend wordpress-nw post.nw

  • langify-nw script
  • wordpress-nw script
  • tee-nw script useful for debugging noweb streams
  • post.nw literate source for this post (technically, I tweaked it a bit after proofreading without going back to the source combining the first two paragraphs and changing <h2>’s to <h3>’s and adding this parenthetical)

The langify-nw script guesses the language for each chunk based on the filename extension on the top-level chunk that incorporates that chunk. That’s why I used filename extensions on the top-level chunks in this post.

An Example

Several months back, I posted some code for rendering anti-aliased text in OpenGL. At the bottom of that post, I had an unwieldy 33-line function that you have to scroll to see with the way my blog is styled.

This would have been an excellent candidate for literate programming. Here is that same function broken up with noweb chunks with some descriptive text sprinkled between chunks.

At the heart of the algorithm, I need to take some point <px, py, pz>, run it backwards through all of the projection matrices so that I have it in pixel coordinates, and calculate the distance between that and the screen coordinates of the origin. So, I have this little function here to do that calculation given the object-local coordinates <px, py, pz> and the origin’s screen coordinates <ox, oy, oz>. 

;;; dist-to-point-from-origin labels decl
(dist-to-point-from-origin (px py pz ox oy oz)
   (multiple-value-bind (nx ny nz)
       (glu:un-project px py pz
                       :modelview modelview
                       :projection projection
                       :viewport viewport)
     (dist nx ny nz ox oy oz)))

That, of course, also needs to determine the distance between two three-dimensional points. For my purposes, I don’t need the straight-line distance. I just need the maximum delta along any coordinate axis. 

;;; dist labels decl
(dist (x1 y1 z1 x2 y2 z2)
   (max (abs (- x1 x2))
        (abs (- y1 y2))
        (abs (- z1 z2))))

Also, to do those reverse-projections, I need to retrieve the appropriate transformation matrices. 

;;; collect projection matrices
(modelview (gl:get-double :modelview-matrix))
(projection (gl:get-double :projection-matrix))
(viewport (gl:get-integer :viewport))

Once I have those pieces, I am just going to collect those matrices, unproject the origin, then find half of the minimum unprojected distance of the points <1, 0, 0> and <0, 1, 0> from the origin. 

;;; calculate-cutoff.lisp
(defun calculate-cutoff (font-loader size)
  (gl:with-pushed-matrix
    #<:use "scale based on font-size">
    (let (#<:use "collect projection matrices">)
      (labels (#<:use "dist labels decl">
               #<:use "dist-to-point-from-origin labels decl">)
        (multiple-value-bind (ox oy oz)
            (glu:un-project 0.0 0.0 0.0
                            :modelview modelview
                            :projection projection
                            :viewport viewport)
          (/ (min (dist-to-point-from-origin 1 0 0 ox oy oz)
                  (dist-to-point-from-origin 0 1 0 ox oy oz))
             2)))))))

Oh, and being the tricksy devil that I am, I scaled things based on my font size before doing any of that. 

;;; scale based on font-size
(let ((ss (/ size (zpb-ttf:units/em font-loader))))
  (gl:scale ss ss ss)

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.

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.

Burnt Paper plugin for GIMP February 16th, 2010
Patrick Stein

Yesterday, I decided to make the images in my article look like they were on old, burnt paper. I did this manually in the GIMP.

I liked the effect, but I didn’t want the tedium of having to do all n steps manually next time I go to use it. So, I wrote a GIMP plugin script to do it.

Here is an example of the plugin script in action. As you can see, I started with a text layer and a selection that was bigger than the text layer. The plugin uses the selection size as original edge of the paper (original, as in before the paper was burned).

And, here is the resulting image:

Here is the Burnt Paper plugin script. Plop this in a directory that’s in your script search path and refresh GIMP’s scripting and then you’ll find it in the Filters > Decor menu. [You can see the script search path by going to Edit > Preferences and selecting Scripts under Folders in the left sidebar. And, you can refresh the scripts by going to Filters > Script-Fu > Refresh Scripts.]

Speedy iPhone App Programming February 4th, 2010
Patrick Stein

Sunday, I decided that I needed a simpler statistics tracking program to keep track of stuff while I’m coaching volleyball. I started out keeping them on paper, but felt that I was staring at the page too often to find where to put a tick mark.

Next, I tried the iVolleyStats Match iPhone app. It is pretty reasonable to use, but it’s got too many controls on the user-interface. The only way that I could keep up with a match was to forgo half of the functionality… either ignoring who is getting credit for an act, ignoring passing stats altogether, and not recording attack or block attempts at all.

For the past few weeks, I have tried using the Voice Memos application on the iPhone. I narrate the game into my phone as the game goes on. This lets me get really fine resolution of statistics, but it doesn’t give me any information in real-time. When I call a time-out, I am going from memory to say how we’ve been passing or hitting. This takes away the lion’s share of the benefit one gets from gathering statistics at all.

So, my team has a tournament this Saturday. I decided Sunday night that I should try to get together an iPhone app that does what I want. I’ve long been thinking about what I want in a volleyball stat tracking iPhone app. What I want will be a big, big undertaking (read: longer than one week). So, I started studying Apple’s CoreData APIs on Sunday night and Monday morning. Then, I dove in.

Now, my previous application was based upon Cocos2D-iPhone. As such, it didn’t involve any of the Apple UIKit classes or any work with Interface Builder. This application is navigation based with table views and custom table view cells from separate NIB files.

Despite this being my first real foray into the UIKit and CoreData APIs, I’ve got an application that I can use on Saturday. There are two more bits that I will try to add tomorrow, but that I don’t need for Saturday. To package it up for sale, there’s more functionality that I’ll need to add in case you don’t like things in the order that I have them on the screen or in case you want to add your own categories of statistic. And, I need to make some specialized visualization screens for some of the stats.

The screenshot here is the main stat-tracking interface. The stats present are Penn State’s stats from my trial run watching game one of their NCAA semifinal against Hawaii from last December. In retrospect, I think I probably gave them credit for two neutral attacks that I should have called free balls. Other than that, I think it’s pretty good. It’s definitely information that will do me well during time-outs.

I fought for a long time this morning trying to get my UIBarButtonItem to show up in my UINavigationBar for one screen. It turns out that these two methods don’t quite do the same thing on iPhoneOS 3.1.2:

// working version that shows my UIBarButton in the UINavigationBar
- (void)showStatTrackingScreen {
    [navigationController setViewControllers:[NSArray arrayWithObject:homeViewController] animated:NO];
    [navigationController pushViewController:trackStatsController animated:YES];
}
 
// version made of fail that does NOT show my UIBarButton in the UINavigationBar
// until you go forward a screen and pop back to this one.
- (void)showStatTrackingScreenMadeOfFail {
    [navigationController setViewControllers:[NSArray arrayWithObjects:homeViewController,
                                                                       trackStatsController,
                                                                       nil]
                                    animated:YES];
}

Updates In Email

Email:

RSS Feeds

l