Inspired by what Smalltalk and Ruby have to give, I started designing my own language, heavily influenced by those two great, very dynamic, truly object-oriented programming languages and came up with a quite simple language named blockd.

The name is based upon the main principle of the language: Everything is an object, and in the end, all code is defined within blocks – that are ruby / smalltalk like blocks. Naming these blocks is done via simple assignment. So instead of having a huge amount of keywords, the language itself is pretty simple, because all we really need is a way to describe assignments, instantiate objects and easily create blocks to pass to methods or use in an assignment.

So in contrast to Ruby, where there are procs, lambdas and blocks, blockd only knows blocks, which basically behave like Smalltalk like blocks – they simply are anonymous procedures / blocks of code (or functions, if you want to call them that – although not pure as in Haskell).

The syntax is a mix of Ruby’s and Smalltalk’s with some minor tweaks I thought would be cool (or not? I don’t know ).
To give you an example of how the language looks, here is a small snippet of some sample code, that actually doesn’t work yet but might do so in the future

# this is just for demonstration
# there probably won't be the need to require the console module from the
# standard library every time you want to print something to the screen ;)
System require: "console"
 
# we support ruby-style blocks with do ... end and curly braces { ... }
File open: "test.txt" mode: "w" do |f|
  f puts: "what's up, dog?!"
  f puts: "crazy shit, yo!"
  f puts: "hahaha!!"
end
 
10 to: 0 do |i|
  Console puts: i
end
 
i = 0
(i < 10) while_true: do |i|
  Console puts: i
  i incr
end
 
numbers = [1,2,3,4,5] select: {|i| i < 3}
numbers each: do |i|
  puts i
end
 
(1 .. 100) each: {|i| Console puts: i}
 
squares = (1 .. 100) collect: {|i| i * i}
 
# define a square method
square = { |x|
  x * x
}
 
# or like this:
abs = { |num|
  (num > 0) if_true {
    return num
  }
 
  num * -1
}

I’m still tweaking the syntax and haven’t decided upon all things completely yet, but I guess I’ve found the pretty basic “feel” of it.

While I haven’t shown you any code that defines a class or modules, it still does show a little of the languages syntax. I’ve started the parser today and it successfully parses the code above, meaning, that since the syntax isn’t too complicated, I expect to be able to parse all the remaining stuff (classes & modules and some minor other things) pretty soon. I then intend to start writing the actual implementation – an interpreter written in Ruby. While I could come up with my own runtime, class library etc, I want to make use of the Ruby infrastructure as much as possible. For one reason, it makes it easier to actually implement something useful, on the other hand, since the language is very close to Ruby’s object model and semantics, I hope I can use most of Ruby’s code directly. This also would mean, that the interpreter could also run on other Ruby implementations like JRuby, IronRuby etc. And maybe, some day, it could also run natively compiled with the Ruby compiler I’ve been working on recently as well – but that’s still far into the future, since the compiler isn’t finished yet.

I guess that’s it for now. More to come soon

I’ve been trying out Clojure lately. Clojure is a new lisp dialect, that is hosted on the JVM and interoperates nicely with it. You can easily use Java methods, classes and libraries. I’ve been using it a little bit, watching some videos about it on blip.tv by it’s author, Rich Hickey, which really is a brilliant guy. You should check them out as well, they give you a pretty good introduction to the language.

Compared to Common Lisp, which I really like allot as well, Clojure does feel a little bit more modern. For example, being not limited to reader support for lists, but also having maps and vectors (like arrays) as first class citizens, is really nice. And then theres the huge emphasis on multithreading support in a really nice way without locks and condition variables but with a stm (software transactional memory). Clojure is a functional language and focuses on immutability of data structures compared to Common Lisp, which also allows a more imperative style, if you want to. In Clojure, you’re forced to a functional style, which might seem like a downside at first, but which makes it possible to have some pretty neat features concerning multithreaded programming support. Since all the datastructures are immutable, there’s no need do use locks when having multiple threads sharing them. I suggest checking out the videos and to give Clojure a try. It seems very promising and it’s having quite a publicity boost right now. Just google for it, take a look on some mailinglists or checkout reddit etc. You’ll find plenty comments, links and blogposts about it (like this one ).

So since I thought it’s always nice to try to port an existing little application from a language I already know to a new one I want to learn, I tried to port a very small programm CallToPower, a collegue from university, wrote and posted on his website. I pretty much copied it straightly to Clojure, changing some parts.

Now I know this might not be the best way to write it in Clojure. But it was my real first (although very small) programm in Clojure and I wanted to make it as close to the original, as possible. Basically, what it does is display some values of some system properties you can choose by pressing the appropriate. Nothing fancy, but it shows some Clojure related stuff pretty well.

So here’s the code, use it as you like:

(ns sysinfo
  (:gen-class)
  (:import (java.awt BorderLayout
		     GridLayout)
	   (java.awt.event ActionEvent
			   ActionListener)
	   (javax.swing JFrame
			JPanel
			JLabel
			JButton)))
 
(def *x-coord* 30)
(def *y-coord* 30)
(def *width* 800)
(def *height* 230)
(def *prog-name* "SysInfo 1.0 [Clojure]")
(def *visible* true)
(def *resizable* true)
(def *frame* nil)
 
(def *label-property-mappings*
     { "OS Name" "os.name",
       "OS Architecture" "os.arch",
       "Java Classpath" "java.class.path",
       "Java Version" "java.version",
       "Current working directory" "user.dir",
       "Resize to default" "Resize to default",
       "Clear" " "})
 
(defn resize-frame
  [frame a b awidth bheight]
  (doto frame
    (.setBounds a b awidth bheight)))
 
 
(defn set-label-text [label text]
  (doto label
    (.setText text)))
 
(defn button-listener
  "Returns a ActionListener, which sets the text of the content label (label-content)
  to the appropriate system property (System.getProperty)."
  [property label frame]
  (proxy [ActionListener] []
    (actionPerformed [evt]
		     (let [system-property-value (. System getProperty property)]
		       (if (not (.equalsIgnoreCase property "Resize to default"))
			 (if (not (.equalsIgnoreCase property " "))
			   (set-label-text label (str (.getActionCommand evt) ": \n" system-property-value))
			   (set-label-text label property))
			 (resize-frame frame *x-coord* *y-coord* *width* *height*))))))
 
 
(defmacro doto-each
  "Macro, that works like doto-macro, only that it does it for each object in objects.
  varname is bound to each object in turn inside of the body (forms) and can be used to access the current
  object, if needed."
  [[varname [& objects]] & forms]
  `(do
     ~@(map (fn [f] `(let [~varname ~f]
		       (doto ~f
			 ~@forms)))
	    objects)))
 
(defmacro add-each
  "Macro, that calls .add on to-object with each object in objects."
  [to-object [& objects]]
  `(do
     ~@(map (fn [o] `(.add ~to-object ~o))
	    objects)))
 
(defn create-new-sysinfo-window
  "Creates the main form and returns it. Mainly GUI-related stuff (javax.swing)."
  []
  (let [frame (JFrame. "Adztec-Independent.de: SysInfo Clojure-style!")
	panel-header (JPanel.)
	panel-main (JPanel. (BorderLayout.))
	panel-left (JPanel. (GridLayout. 6 1))
	panel-south (JPanel. (GridLayout. 1 1))
	;; labels
	label-header (JLabel. "System Information")
	label-blank (JLabel. " ")
	label-content (JLabel. " ")
	label-adztec-indep (JLabel. "by www.adztec-independent.de")]
 
    (.setHorizontalAlignment label-blank (JLabel/CENTER))
    (.setHorizontalAlignment label-adztec-indep (JLabel/CENTER))
 
    ;; buttons
    (let [btn-java-cp (JButton. "Java Classpath")
	  btn-java-version (JButton. "Java Version")
	  btn-os-name (JButton. "OS Name")
	  btn-os-arch (JButton. "OS Architecture")
	  btn-current-working-dir (JButton. "Current working directory")
	  btn-resize-to-default (JButton. "Resize to default")
	  btn-clear-all (JButton. "Clear")]
      (do
	;; add button-listener to all buttons
	(doto-each  [btn [btn-java-cp
			  btn-java-version
			  btn-os-name
			  btn-os-arch
			  btn-current-working-dir
			  btn-resize-to-default
			  btn-clear-all]]
 
		      ;; add listener to button
		    (.addActionListener
		     (button-listener (get *label-property-mappings* (.getText btn)) label-content frame))))
 
	;; add buttons to panel
	(add-each panel-left
		  [btn-java-cp
		   btn-java-version
		   btn-os-name
		   btn-os-arch
		   btn-current-working-dir])
	(add-each panel-south
		  [btn-resize-to-default
		   btn-clear-all])
 
	;; add labels to panel
	(add-each panel-header
		  [label-header
		   label-blank])
	(.add panel-south label-adztec-indep)
 
	;; pack on frame
	(let [content-pane (.getContentPane frame)]
	  (add-each content-pane
		    [panel-main
		     label-content])
	  (doto content-pane
	    (.add BorderLayout/NORTH panel-header)
	    (.add BorderLayout/WEST panel-left)
	    (.add BorderLayout/SOUTH panel-south)))
	(doto frame
	  (.pack)
	  (.setTitle *prog-name*)
	  (resize-frame *x-coord* *y-coord* *width* *height*)
	  (.setVisible *visible*)
	  (.setResizable *resizable*)
	  (.setDefaultCloseOperation JFrame/HIDE_ON_CLOSE)))
    frame)) ;; return frame
 
 
(defn -main
  "Main function. Gets called by the system, if used as an executable .jar file."
  []
  (let [*frame* (create-new-sysinfo-window)]
       (. Thread (sleep 100))))

The problem with anonymous lambda functions is, that they can’t call themselves recursively, since – well they’re anonymous and hence don’t have a name. To get passed this problem, you can let it have an additional function parameter which it will call in place where the recursion would normally take place.

An example for a reverse function, which reverses the elements of its argument (a list) with the help of an accumulator list (which holds the reversed list) could be written like this, without using an additional function:

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(defun myreverse (list &optional (acc nil))
  (let ((head (car list)) (rest (cdr list)))
    (cond
      (head
       (cond
	 ((atom head)
	  (myreverse rest (cons head acc)))
	 (t
	  (myreverse rest (cons (myreverse head) acc)))))
      (t
       acc))))

But, as you can see, the accumulator list is part of the function’s argument list, although optional. To make this function a little bit ’safer’, it shouldn’t be part of the ‘public interface’ of the function. So you’d probably come up with something like this, where you’d use an anonymous helper function, which takes the additional accumulator list and returns it when it’s done reversing the original list:

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(defun myreverse (list)
  (let ((reverse-acc #'(lambda (func list acc)
			(let ((head (car list)) (rest (cdr list)))
			  (cond (head
				 (cond ((atom head)
					(funcall func func rest (cons head acc)))
				       (t
					(funcall func func rest (cons (funcall func func head nil) acc)))))
				(t
				 acc))))))
    (funcall reverse-acc reverse-acc list nil)))

But, as you can see, since anonymous functions can’t call themselves recursively, you need to give it another extra parameter, a function object, which actually gets filled with the anonymous function itself, so it can call itself inside its body. But, fortunately, theres an even better version how to do exactly this in lisp: With the labels special operator, which defines local functions with a given name (like normal functions) which can then get called inside the function body itself and in the body-form of the macro:

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(defun myreverse (list)
  (labels ((myreverse-acc (list acc)
	     (let ((head (car list)) (rest (cdr list)))
	       (cond (head
		      (cond ((atom head)
			     (myreverse-acc rest (cons head acc)))
			    (t
			     (myreverse-acc rest (cons (myreverse-acc head nil) acc)))))
		     (t
		      acc)))))
    (myreverse-acc list nil)))

As you can see, this version is nicer than the first or the second, since it hides the fact, that the reverse function uses an accumulator list and that it is also easier to understand, since you can use an actual name for the function instead of passing the function as an argument to itself, in ordner to make a recursive call. So basically, you can think of a function defined with the labels special operator as a local defun, which I think is really nice.