You are the wolf

Setup mods (clojure)

2009-01-18T00:40:00.001-08:00

After much tearing of hair, many emacs restarts, many killings of *inferior-lisp*, I finally decided to give up on the pure-swank way of calling java. Up until yesterday I just had this:

  
(setq swank-clojure-jar-path "/home/joseph/src/clojure/clojure.jar")
(setq swank-clojure-extra-classpaths 
      (list "/home/joseph/clojure/clojure-contrib.jar" 
            "/home/joseph/lib/commons-httpclient-3.1.jar"))

Last night I reorganized everything basically following Bill Clementson's setup. Now all the classpath business goes into an environment variable and gets called by an almost empty shell script. For me, the main advantage of this setup is that it was easier to see how java was being called, so that it was easier to debug the rest of my setup.

To make a long story short, I was finally able to import org.apache.commons.httpclient this morning.

recur is a trip

2009-01-16T14:08:00.001-08:00

This is really just an update to my previous post, but I just added recur to my recursive function.

The Clojure documentation isn't that verbose, in general, and it took my n00b brain some time, and some luck, and some nasty messages from the compiler, to figure out how you actually use recur. Basically, it looks like that, just as you are about to have your function call itself, instead of using the name of your function, you call recur instead. Wow. Why does that seem cool?

Baby clojure step number two: my very first mind expansion

2009-01-16T09:18:00.001-08:00

So, today, after just a little bit more fiddling getting Clojure/swank/slime working on my desktop box, I was able to actually run into a more Clojurish obstacle. But first I had better explain my little project that I just mentioned yesterday.

I used to read RSS feeds with Gnus, but ever since I switched to using the Gmail IMAP interface with Gnus (rather than fetching mail to my local server and reading it from there), the extra time spent reloading all my feeds every time I wanted to check my mail started to discourage me. And that was the end of nnrss for me. At least for awhile.

The other day I started to think that nnrss might work for me again if I kept local copies of the feeds and used wget or something to keep them up to date. As I started putting a bash script together, I started to realize that my specs were quickly surpassing my bash skills: keeping track of the last time fetched (because wget won't do it if you change the name of the file you download, which you have to do because feeds often have the same filename...), conditionally running Atom feeds through an XSL stylesheet to make them readable for nnrss, and probably more as the list got longer. And I did look around for some kind of ready-made solution to all of this but everything I found was somehow too complete. So just as I was about to start writing some Perl, I thought: "you're in no hurry, do this in Clojure and learn a thing or two". So here I am.

Anyway, step one right now is to read a text file with a list of URLs and a feedname. Next I will add a "type" field or maybe an "atomp" field to pick out those that need furthing parsing. So then we end up looking at ideal material for a Perl one-liner but a metaphysical challenge for the Clojure 00ber-n00b that I am. Yesterday I mentioned my first flailings that got me as far as reading a file, splitting the lines and printing them back out. Heady stuff, I know.

Today's challenge was stuffing everything back into what was to become my feed "database". Using Stuart Halloway's rewrite of Peter Seibel's PCL, specifically the now-famous CD database, I had settled on using a set of structs to contain all my information.

Everything seemed very calm and smooth for awhile. I could write functions for making structs, adding them to the set (#{}). I could read my data file, I was using first and second and felt like I was back in Lisp.

And then suddenly I hit the wall of immutability.

Here is what I wanted to do:

  
(defn parse-rsslist-file [db feedlist-filename]
 (with-open [r (reader feedlist-filename)]
   (doseq [line (line-seq r)]
     (let [url (first (.split line " "))
           nam (second (.split line " "))]
       (add-feeds db (struct feed nam nil url nil)))))
       db)

I was stupidly trying to loop through the lines and accumulate the results in db. That is what I would have done in Common Lisp and just about anything else. When my function kept just returning an empty #{}, I finally realized that I was face to face with real functional programming and one of the aspects of Clojure that has been commented the most.

This led to a new exploration of the Clojure docs and a tentative understanding of the difference between a sequence and a collection and a list. I knew that I needed to write a recursive function but I was not sure exactly what (line-seq r) was spitting out. Happily for me, it turns out that everything does end up working more or less like a list, and so with very little fiddling I was able to get my magnificent file reading function to work.

Behold!

    
(defn parse-rsslist-file [db urlfile]
  (with-open [r (reader urlfile)]
    (parssrss db (line-seq r))))

(defn parssrss [db sq]
  (if (not sq)
    db
    (parssrss (db-add-line db (first sq)) (rest sq))))

(defn db-add-line [db line]
  (let [lspl (.split line " ")]
    (cons (struct-map feed 
                  :name (second lspl)
                  :title nil
                  :url (first lspl)) db)))

Tiny baby clojure steps

2009-01-15T10:36:00.001-08:00

Yesterday I started actually trying to do something with Clojure. Here are my very, very first impressions of what it is like to actually get your feet wet, or your fingers dirty or whatever. This can probably all be resumed with: everything is much more difficult if you don't have any experience with Java. Like me.

This is of course assuming that your system is working correctly. I only finally ended up getting slime, swank and clojure all working together correctly. It isn't that hard, or at least it doesn't seem like it once you see how things fit together. Just a couple of variables for swank, your .jars in a good spot and you are ready to go. It took me a while to realize that of course. And I made stupid mistakes like not compiling clojure-contrib yet expecting it to work. Stupid stupid mistakes.

My initial task was to try to read a file line-by-line. A very Perl-ish thing to do I guess, but it seemed to be a reasonable thing to do. Also, in the initial version of my little project (more about that later), everything started with a config file full of URLs that I was trying to read with bash.

So how do you read a file line by line in Clojure?

Well, here is what I have right now. It works.


(use '[clojure.contrib.duck-streams :only (reader)]) 
(with-open [r (reader "/home/joseph/localrss/rss_urls")]
        (doseq [line (line-seq r)]
          (println line)))

What is strange is that Java is always close by. Just for reading a file, you need Java objects. Here "duck-streams" are a wrapper around some Java stream things. And I had to bring the clojure-contrib .jar into my configuration for this to work. This is just something to get used to, I suppose, and probably feels perfectly natural for Java programmers.

The same seems to go for string functions. The official docs just say :

Clojure strings are Java Strings. See also Printing. user=> (map (fn [x] (.toUpperCase x)) (.split "Dasher Dancer Prancer" " ")) ("DASHER" "DANCER" "PRANCER")

Those

.toUpperCase

and

.split

s look suspiciously like macros calling Java functions, so it looks like I'll be getting chummy with those soon too.

Interestingly, I haven't seen anything about strings being vectors or sequences of some kind, as in Common Lisp. I guess all of that gets thrown away once you beat into your n00b brain that "Clojure strings are Java strings".

The pros from Dover

2008-05-05T12:51:00.001-07:00

Is this sounding like one long rant about php?

I wonder why...

Today's rant is about the quality of PHP documentation. I've taken to using the official PHP documentation on the official website. Fairly often I am disappointed because there are missing parts: the developers wrote some code quickly and didn't bother to document. Odd for an official site, but okay.

So right now I am looking for info on doing HTTP digest authentication in php. There is a page about it that provides some examples that simply don't work. The regex for parsing Authorization headers is defective and none of the solutions people have offered up in the comments have helped me at all...

Fine.

The funny thing is that everyone insists on using regexes. I like regexes just fine, and with Perl I used to consider myself reasonably good with them. Anyhow, the consensus seemed to be that you needed a good regex. After screwing around for awhile, I was about to write my own solution using explode and substr and a lot of strpos(). But it was getting late...

So, after wasting an evening thinking that there was something I wasn't getting, I decide to look around for a library. There isn't much that jumps out at me right away, but I end up finding Auth HTTP which extends the Auth class.

I don't want to install Auth (trying to go light) but I download Auth HTTP to look at how they parse the Authorization header. First of all, I am impressed by how clean the code is. Then I find my function, and guess what: explode, substr, strpos.

For instance (more about functions as arguments)

2008-04-27T13:03:00.001-07:00

So, passing functions as arguments by turning them into strings, that's fine I suppose for traditional functions. But what about object methods? How am I supposed to transform $obj->do_something() into a string that I can feed to another function? That is what I would like to know.

php5 makes php bearable

2008-04-27T07:22:00.001-07:00

Just to show what an amazingly open mind I have, I just wanted to add that after moving to php5 and trying to be as object-oriented as I can, I have started to find that programming in php can be less painful than I originally thought.

I am starting to get used to some of the overall quirkiness of the language. I even forgive it for having so ding many functions, since Common Lisp has quite a few as well.

Overall, I find that there is a lack of coherence in the way the function are implemented. I still have to look everything up all the time, but that is probably just me. However I expect a function to work, php usually does the opposite. But hey, they wrote the language, so they can do what they want. More substantially, I find completely counterintuitive and backwards the way that you pass functions as string arguments. At least in Perl, even though all arguments are passed as values, you are passing a reference, not just a string name. It just feels wrong, I'm telling you! I'd be willing to make function objects and pass them instead, but you still would have to feed those objects with strings naming functions... so back to square zero.

From 4 to 5

2008-04-13T06:22:00.001-07:00

Well, I get to play with php5 instead of php4. This is huge news for me, as I intend to use stored procedures in MySQL, which is all but impossible with php4.

I'm taking advantage of this change to really make this new project object-oriented. I'm not much of an OOP fanatic myself, but I do see some advantages here, especially since it is so ding hard to write anonymous functions and to pass them around. (At least that is my impression.) php5 seems set up in a way that encourages you to pass objects around instead, so I will adjust.

Testing... Testing...

2008-03-24T10:25:00.001-07:00

Now that I have started using a test suite -- this one, in fact -- my life has improved. At least I can see why PHP is not doing what I want it to.

There is something very satisfying about testing as you go. It definitely improves the modularity of your code.

strlen!

2008-03-24T09:02:00.001-07:00

So strlen is just way more intuitive than length()!

Obviously

2008-03-24T07:36:00.001-07:00

Obviously, I'm using php4. Because I have to.

If I could use php5, I would.

If I could use (almost) anything besides, php, four or five, I would. Including languages I don't even know but would love to learn. Python, for example. That would be fun.

PHP rant : anonymous functions

2008-03-24T07:27:00.001-07:00

Anonymous functions in PHP are a joke. Maybe not in their overall functionality but at least in their syntax, that is with create_function. I mean, really: the function is a string of code that somehow gets evaled into a function?

If you are going to have anonymous functions, it would be nice to be able to write them like functions.

Hey...

2008-03-24T07:21:00.001-07:00

This is obviously my first post here. This blog is going to be about programming. Right now it is going to be about why I hate the php programming language. That is why I decided to create this blog today. I would have eventually done it anyway, but it would have been later. So there you are. I'm going to publish this and then go see what this thing looks like. Back with some rants quickly.