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Postings from July 2002
(I don't have the original msg in my mbox, so I'm jumping in here...) The following is from the Tcl bytecode compiler [1] FAQ: Why doesn't Tcl use the Java bytecodes? I [2] had originally hoped to use Java bytecodes because they have a mature design and because Java is widely available. I chose to use my own Tcl-specific bytecodes because I was concerned that using the Java virtual machine would be too slow or take too much memory. The basic problem is the semantic mismatch between Java bytecodes and Tcl. Consider the Tcl set command. Tcl variables behave very differently than Java variables. I can't use a Java instruction like astore (store object reference in local variable) to store a Tcl value into a Tcl variable since it doesn't handle by itself such Tcl details as variable traces, unset, or global. The best I could do would be to translate a Tcl set command into a sequence of several Java instructions that did the appropriate checks. Unfortunately, the number of Java instructions to implement each Tcl command would make the compiled program too big. A more realistic scheme is to generate Java bytecodes that call one or more Java methods to do the actual work for each Tcl command. With this number of Java method calls, acceptable performance will depend on using a Java JIT (bytecode-to-machine code) compiler. With Java JIT compilers becoming more widely available this might be realistic. One possibility would be to translate the relatively high-level Tcl bytecodes into Java bytecodes. However, there is another problem with using Java bytecodes. Much of the interesting code in Tcl/Tk and its extensions is in C. Java code can call native methods implemented in C, and vice-versa, but this is awkward, not portable, and the capability is disabled in Netscape (and many other Java implementations) for safety reasons. [1] http://www.tcl.tk/doc/compiler.html [2] Author credit on the document is brian.lewis@eng.sun.com __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.comThread Previous | Thread Next