DECEMBER 29TH, 2012
By AMBS
In the last two days I engaged in developing Reversi, just to learn how the minimax algorithm works. To make it easier to share, and remove GUI toolkit dependencies, my approach was using HTML (a simple page with a 8×8 table), three images (empty cell, black or white cells), a CSS file that fills empty cells or used cells, and highlights movement possibilities, and a couple of JavaScript files (jquery, a reversi-board.js file to handle the board as an object, a reversi.js file to handle the interface between the board and the HTML file, and finally a minimax.js file to handle the minimax algorithm.
At the moment the game is playable, and not too slow. The code can be optimized to make it faster. In the next couple of days I might do that.
Also, regarding the AI code, it can be made better. In one side, the minimax algorithm can try to analyze more moves in advance (only three at the moment), in the other, the board evaluation function can be made better as well.
If you wish to play, go ahead: http://eremita.di.uminho.pt/~ambs/reversi
I can’t see how people say Java is an end-user language, whose applications are for general user usage…
SEVERE: Exception
javax.xml.transform.TransformerException: org.apache.fop.fo.ValidationException: "fo:inline" is not a valid child of "fo:block"! (See position 1870:716)
at org.apache.fop.cli.InputHandler.transformTo(InputHandler.java:302)
at org.apache.fop.cli.InputHandler.renderTo(InputHandler.java:130)
at org.apache.fop.cli.Main.startFOP(Main.java:174)
at org.apache.fop.cli.Main.main(Main.java:205)
Caused by: javax.xml.transform.TransformerException: org.apache.fop.fo.ValidationException: "fo:inline" is not a valid child of "fo:block"! (See position 1870:716)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(TransformerIdentityImpl.java:501)
at org.apache.fop.cli.InputHandler.transformTo(InputHandler.java:299)
... 3 more
Caused by: org.apache.fop.fo.ValidationException: "fo:inline" is not a valid child of "fo:block"! (See position 1870:716)
at org.apache.fop.events.ValidationExceptionFactory.createException(ValidationExceptionFactory.java:38)
at org.apache.fop.events.EventExceptionManager.throwException(EventExceptionManager.java:54)
at org.apache.fop.events.DefaultEventBroadcaster$1.invoke(DefaultEventBroadcaster.java:175)
at $Proxy1.invalidChild(Unknown Source)
at org.apache.fop.fo.FONode.invalidChildError(FONode.java:534)
at org.apache.fop.fo.flow.Inline.validateChildNode(Inline.java:123)
at org.apache.fop.fo.FOTreeBuilder$MainFOHandler.startElement(FOTreeBuilder.java:267)
at org.apache.fop.fo.FOTreeBuilder.startElement(FOTreeBuilder.java:171)
at org.apache.xalan.transformer.TransformerIdentityImpl.startElement(TransformerIdentityImpl.java:1072)
at org.apache.xerces.parsers.AbstractSAXParser.startElement(Unknown Source)
at org.apache.xerces.xinclude.XIncludeHandler.startElement(Unknown Source)
at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(TransformerIdentityImpl.java:484)
... 4 more
---------
javax.xml.transform.TransformerException: org.apache.fop.fo.ValidationException: "fo:inline" is not a valid child of "fo:block"! (See position 1870:716)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(TransformerIdentityImpl.java:501)
at org.apache.fop.cli.InputHandler.transformTo(InputHandler.java:299)
at org.apache.fop.cli.InputHandler.renderTo(InputHandler.java:130)
at org.apache.fop.cli.Main.startFOP(Main.java:174)
at org.apache.fop.cli.Main.main(Main.java:205)
Caused by: org.apache.fop.fo.ValidationException: "fo:inline" is not a valid child of "fo:block"! (See position 1870:716)
at org.apache.fop.events.ValidationExceptionFactory.createException(ValidationExceptionFactory.java:38)
at org.apache.fop.events.EventExceptionManager.throwException(EventExceptionManager.java:54)
at org.apache.fop.events.DefaultEventBroadcaster$1.invoke(DefaultEventBroadcaster.java:175)
at $Proxy1.invalidChild(Unknown Source)
at org.apache.fop.fo.FONode.invalidChildError(FONode.java:534)
at org.apache.fop.fo.flow.Inline.validateChildNode(Inline.java:123)
at org.apache.fop.fo.FOTreeBuilder$MainFOHandler.startElement(FOTreeBuilder.java:267)
at org.apache.fop.fo.FOTreeBuilder.startElement(FOTreeBuilder.java:171)
at org.apache.xalan.transformer.TransformerIdentityImpl.startElement(TransformerIdentityImpl.java:1072)
at org.apache.xerces.parsers.AbstractSAXParser.startElement(Unknown Source)
at org.apache.xerces.xinclude.XIncludeHandler.startElement(Unknown Source)
at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(TransformerIdentityImpl.java:484)
... 4 more
---------
org.apache.fop.fo.ValidationException: "fo:inline" is not a valid child of "fo:block"! (See position 1870:716)
at org.apache.fop.events.ValidationExceptionFactory.createException(ValidationExceptionFactory.java:38)
at org.apache.fop.events.EventExceptionManager.throwException(EventExceptionManager.java:54)
at org.apache.fop.events.DefaultEventBroadcaster$1.invoke(DefaultEventBroadcaster.java:175)
at $Proxy1.invalidChild(Unknown Source)
at org.apache.fop.fo.FONode.invalidChildError(FONode.java:534)
at org.apache.fop.fo.flow.Inline.validateChildNode(Inline.java:123)
at org.apache.fop.fo.FOTreeBuilder$MainFOHandler.startElement(FOTreeBuilder.java:267)
at org.apache.fop.fo.FOTreeBuilder.startElement(FOTreeBuilder.java:171)
at org.apache.xalan.transformer.TransformerIdentityImpl.startElement(TransformerIdentityImpl.java:1072)
at org.apache.xerces.parsers.AbstractSAXParser.startElement(Unknown Source)
at org.apache.xerces.xinclude.XIncludeHandler.startElement(Unknown Source)
at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
at org.apache.xalan.transformer.TransformerIdentityImpl.transform(TransformerIdentityImpl.java:484)
at org.apache.fop.cli.InputHandler.transformTo(InputHandler.java:299)
at org.apache.fop.cli.InputHandler.renderTo(InputHandler.java:130)
at org.apache.fop.cli.Main.startFOP(Main.java:174)
at org.apache.fop.cli.Main.main(Main.java:205)
Just great. Now I know exactly what to do. Cry!
DECEMBER 21ST, 2011
By AMBS
This year I am teaching Artificial Intelligence for Games. I grabbed some book PDFs from the Internet (yes, sorry, it would be impossible to buy all the books to choose one, and libraries around doesn’t have books in this thematic) and I chose a pair of books to buy. One of them is this Artificial Intelligence for Games
, by Ian Millington and John Funge.
The book is quite complete, the language very accessible, full of code, lots of insights about that developing AI for games means. I really like the book, and I will continue to use in future years if they let me continue teaching this course.
Unfortunately the book is full of small typos and problems. There is an official errata available but it is very incomplete. I started writing my own errata (I’m not repeating the items in the official errata, just adding new errors I find) with some fixes, and some insights on some interpretation problems. I warned Ian Millington about my errata, and he will, hopefully, go through my errata items and decide if they should be included in the official errata. While Ian doesn’t have the time for that, I am sharing my own errata page. Note that I am not professional on this area and I might have misunderstood something…
OCTOBER 11TH, 2010
By AMBS
Probably this is a stupid rant/question. If so, please clarify me. I can live without the insults. Really 
OK, on to the relevant stuff. Twitter has a new OAuth authentication mechanism. To write an application able to post on twitter your application need to be registered and have a consumer key. That key is used to identify your application to twitter when requesting permissions to a user to post using her credentials.
Now, the problem is when your application is written in a scripting language, like Perl, Python, Ruby or anything similar. Will you insert this key verbatim in the source code? Then, when shipping your app, others can grab that token and use it as if it were your app. You can encrypt it, but you need to ship the decryption algorithm as well, so, making the key verbatim.
One of two things can be happening: or twitter guys are not good on this API thing, or I am being totally stupid.
OCTOBER 2ND, 2010
By AMBS
If you know me, you know that I program mainly C and Perl, that my preferred editor is Emacs, and that I use mostly Mac OS X for that task.
But, I teach programming, and sometimes I teach programming to students that never heard of Linux or, worse, that never used the command line of Windows. Given this, I tend to search for simple solutions to help them do not deal with the command line so I can use more time for the task of learning how to program.
With that in mind, I decided to suggest a C IDE for windows. The main IDE (I think) is Visual Studio. Although it is paid, there are protocols between Microsoft and the universities to use their software for free for academic purposes. But the Visual Studio installation disc is some hundreds of megabytes. That is not very portable. Also, the application is quite heavy when running. I decided to search for an alternative, and found DevC++. It is just 10 megabytes of download, uses GCC (or MinGW), and works quite well.
It just have one big and stupid problem. Although DevC++ is being developed for more than a decade, their developers did not implement, yet, a pause mechanism for when you are running a console program. In their faq they suggest to add a ‘system(“PAUSE”)’ in the end of the code. That is just stupid! Why to have to add such a line in your code, just during development, and then remove it when you want to ship the application? It would be quite more interesting to have an option in the IDE to force that window not to close. Some other similar applications, like the Lazarus IDE for Pascal, include that option already.
Now I need to decide if I should go back to Visual Studio, if I should explain why DevC++ doesn’t work properly, and explain how to add a pause at the end of the application, of if I should go back and teach students how to test their applications right from the command line.
CSS Cheat Sheet
I teach XML, DTD and the like, and I teach (or show and make students use) CSS for XML. It doesn’t work properly on all browsers, it doesn’t work consistently on all browsers, it doesn’t do everything web publishing needs. But it is a good approach to add some style and usefulness to XML without teaching XSLT.
Normally I give my students a CSS Cheat Sheet. Usually it is the CSS Cheat Sheet v2 from Added Bytes. This time I googled some more time searching for a better one. Basically, Added Bytes cheat sheet present keywords for CSS properties, but doesn’t describe valid values.
In this quest, I found what I think it the best (ok, one of the best) CSS Cheat Sheet available in the Internet. It is from “A Coding Fool” webpage. It is two pages but I do not see that as a problem, given now most printers do duplex and, if it doesn’t, you can always do that manually. Is just one sheet of paper…
JANUARY 14TH, 2010
By AMBS
I posted some time ago about Pascal, and the nice (and worst) things that Pascal has in its language. I discovered yet another cool thing. Unlike C, where you can pass parameters to functions by value, or using a pointer (and therefore, as reference), in Pascal you can use a value, you can use a pointer, or declare a parameter as a variable. This is similar to passing by pointer, but with a cleaner syntax.
Note the difference between
-
procedure foo(bar: integer);
-
begin
-
bar := 10;
-
end;
and
-
procedure foo(var bar: integer);
-
begin
-
bar := 10;
-
end;
The first procedure does not change anything in the outside world, while the second changes the value of the variable passed as argument.
As expected, the compiler raises an error if you call this second procedure with a constant integer.
NOVEMBER 19TH, 2009
By AMBS
As I posted before, I am teaching Pascal. I could discuss the relevance on teaching this language in this decade, but that is not my concern. I would like just to point The Good, the Bad and the Ugly I find in Pascal.
The Good: Pascal evolved and is a high level language. You have auto-growing strings (ok, with a size limit), you have arrays indexed by characters, integers or enumerated data types. That is good!
The Bad: Pascal syntax continues to be a mess. Begin and End keywords make the code big, the attribution with ‘:=’ makes it easy to type errors, and the low precedence of logic operators make me angry.
The Ugly: I can’t find a clean way to try opening a file without crashing the application. The only method I found (check the bottom of http://www.learn-programming.za.net/programming_pascal_learn10.html needs you to turn on and off compiler flags. That is annoying, stupid and decidedly too low level…
OCTOBER 19TH, 2009
By AMBS
Probably you know that I was a teacher at the Computer Science Department at Universidade do Minho. There I was a C and Perl teacher, as well as other classes that are not relevant for this post. Now, I am working at Instituto Politécnico do Porto, in the Escola Superior de Estudos Industriais e de Gestão. I am not responsible for the class, so I teach what the responsible teacher says. I was quite surprised they still used Pascal.
But this was a stupid question. Now, after getting back to the Pascal world, I noticed Pascal is not dead, and it getting better, and quite far from C when regarding the abstraction layer. I will not discuss efficiency. It I would do that, I would not program Perl anymore.
Pascal is, like C, a compiled language. But it supports growing strings. Strings can be edited as if they were Perl strings. You can add substrings to the string, remove substrings by nothing or other smaller or bigger strings. But you can also use it as an array of characters and access to each character individually. I really miss this feature in Perl.
Pascal is now supporting units as classes. This means it can be programmed as if it were an Object Oriented language. I did not get to that point yet. But it is nice to know Pascal evolved.
Oh, there is a free compiler (free pascal compiler) and there is an IDE (lazarus) that enables GUI application development just like the old Delphi.
