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Michael Chen 的技術文件

程式設計、開放原始碼軟體、技術雜談

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In my previous post, I introduced AI::Prolog, a Prolog engine written in Perl. AI::Prolog is easy to use; however, the speed may be not satisfying. Language::Prolog::Yaswi refers to Yet Another interface to SWI-Prolog; the performance of Language::Prolog::Yaswi is better than that of AI::Prolog. Before using Yaswi, You need a SWI-Prolog complier in your system. You can get it from SWI-Prolog website. First, you need to write a Prolog knowledge base. 繼續閱讀

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Perl programming can be done in imperative, objective and functional styles. However, Perl lacks direct support in logic programming. Prolog is a logic programming language, popular in the fields of natural language processing and artificial intelligence. AI::Prolog is where Perl and Prolog cross. AI::Prolog is a Prolog compiler written purely in Perl and, optionally, comes with aiprolog, a interactive Prolog interface. The module is easy to use if you know 繼續閱讀

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In Perl, you do not need to declare the type of a variable in advance. Sometimes, it is confusing because you do not know the type of the variable and you do not know what method to use. By using ref with a object, you can know the class (or type) of the object. Say we want to extract some data from some xml files. XML::LibXML is Perl binding for 繼續閱讀

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Since hash is a one-way relation, you cannot directly sort by hash values and get hash keys in Perl. However, by customized sort subroutine, you can also sort by hash values. This post shows the trick. You still need hash keys for later use, so we sort hash keys here. The catch is in the by_value subroutine. Here we pass $a and $b to the subroutine and compare them by 繼續閱讀

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According to the official page, rJava is a Low-level interface to Java VM very much like .C/.Call and friends. A strange error occurs while I try to load rJava insido RStudio. Reason: image not found According to the thread, starting RStudio and setting LD_LIBRARY_PATH variable from terminal can solve the problem. $ LD_LIBRARY_PATH=/Library/Java/JavaVirtualMachines/jdk1.7.0_51.jdk/Contents/Home/jre/lib/server: open -a RStudio You may make an alias for the command in ~/.bashrc. 繼續閱讀

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When we want to search from a page, we open the search page and type keywords in the search bar. It is annoying to repeat the process multiple times. Is there faster way to reduce the repeat? Firefox bookmarks comes with a convienent function called keyword search. You can try a built-in keyword search now by typing google keyword in the location bar. ! To use keyword search in Firefox, 繼續閱讀

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Coherent PDF Tools is a command line PDF tool for Windows, Mac and Unix. It is free for non-commercial use. I wanted to remove all bookmarks in the PDF file and re-edit them and Coherent PDF Tools can remove all bookmarks in single command. After some try, it simply worked. Here I introduce how to edit bookmarks with Coherent PDF Tools. This tutorial was tested on OS X 10.9. Coherent 繼續閱讀

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JavaScript is a popular web language initially implemented on Netscape Navigator and later adapted on virtually all browsers. Since a JavaScript engine is a part of a browser, we had to embed JavaScript file in a HTML page, to load the script from the browser, and to use function like prompt() or alert() to receive from and response to developers. Nevertheless, with Node.js, we can program in JavaScript like in 繼續閱讀

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If we want to convert comma- or space-seperated text files to Excel ones, we have to open Excel and do manual conversion. Is there automatic way to do batch conversion? Of course, you can do batch conversion without opening Excel with Data::Table::Excel. Data::Table::Excel is a Perl module to convert between Data::Table objects and Excel (xls/xlsx) files. Data::Table reads CSV, SQL database and Excel files and converts them to CSV, HTML 繼續閱讀