TC Lispers May Presentations online May 27th, 2010
Patrick Stein

The Twin Cities Lisp Users Group meeting for May was last Tuesday.

Teaching Introductory Programming Using Scheme

Daniel Feldman gave this presentation at the TC Lispers meeting in May 2010.

Teaching Introductory Programming Using Scheme on Vimeo.


Robert Goldman gave this lightning talk to the TC Lispers meeting in May 2010.

ASDF2 on Vimeo.

Programming Contest

Patrick Stein gave this lightning talk to the TC Lispers meeting in May 2010.

Programming Contest on Vimeo.

Lightning talk by Patrick Stein to the Twin Cities Lisp Users Group about hosting a Programming Contest. This presentation was recorded on 2010-05-25.

Org-Mode CSS May 13th, 2010
Patrick Stein

The color scheme here is a bit me-centric, but I am mostly posting it because I find the typography pleasing…. In my .emacs file, I have set up the org-export-headline-levels to two and the org-export-html-style to the following:

;;; .emacs.lisp
(setq org-export-html-style
      "<style type="text/css">#<:use "style.css"></style>")

# style.css
<<basic body style>>
<<header style>>
<<content style>>

The basic body has no margin and a pleasing (to me) khaki color.

# basic body style
body {
   background-color: #999966;
   margin: 0em;

The headers are carefully sized to try to take up a multiple of 1.4em with a consistent bottom margin.

# header style
h1 {
   font-size: 2.0em;
   margin-top: 1.9em;
   margin-bottom: 0.3em;
h2 {
   font-size: 1.5em;
   margin-top: 2.4em;
   margin-bottom: 0.3em;
h3 {
   font-size: 1.25em;
   margin-top: 1.25em;
   margin-bottom: 0.3em;

The main body is a pale yellow color with vertical borders. It’s got a decent font (the one that I have by default for my browser) with a slight tweak to the letter spacing and a big tweak to the leading. It keeps from getting too wide and stays centered. Oh, and I don’t skip space before lists.

# content style
div#content {
   background-color: #ffffcc;
   border-left: double #333300 3mm;
   border-right: double #333300 3mm;
   font-family: Times, serif;
   letter-spacing: 0.075em;
   line-height: 1.4;
   margin: 0em auto;
   padding: 2em;
   width: 45em;
ul {
   margin: 0;

Here is some sample output.

Meta News… May 12th, 2010
Patrick Stein

I have switched Web Hosts for my site. It went fairly smoothly (about three hours of moving things around, swapping in new nameservers for my domain, and huzzah). It would have gone even more smoothly if I had noticed the Archive Tool that the new host provides to unzip a whole hierarchy… or if the new host allowed ssh-access so that I could unzip it myself. *shrug* The ssh access would have also been nice for doing the database transfer because phpMyAdmin is subject to timeouts and file-size limits for imports so I had to split –l my way there.

In other news, in a few weeks, I won’t be a stay-at-home dad any longer…. I’ll be out in the workforce. This will probably seriously cramp my productivity here. *shrug*

SLIME/noweb-mode/Lisp tip May 7th, 2010
Patrick Stein

Just a quick tip here if you use SLIME for Lisp and use Lisp as a noweb-code-mode…. Either change slime-auto-connect to 'ask or 'always or just remember to start slime before you wander into a Lisp code chunk. If you don’t, noweb-mode gets all confused and won’t code-highlight your Lisp or switch back to doc-mode when you leave that chunk.

I spent a long time just thinking noweb-mode was entirely broken if there were single quotes or less-than signs in any document chunk. Alas, it just needed SLIME to stop chucking a Not connected error.

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.

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)
    #<: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))

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)