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159 lines
5.1 KiB
Java
159 lines
5.1 KiB
Java
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INTRODUCTION
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This release of Mercury contains a port to Java,
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in particular to Sun Microsystems' Java 2 Platform, Standard Edition (J2SE).
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The Mercury compiler will generate Java source code that can be compiled into
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Java bytecode suitable for running in the J2SE runtime system.
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The port is mostly complete, but some parts of the Mercury standard
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library are not yet implemented (for a full list see the FAQ below).
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The port is currently targeted at J2SE version 1.2 or higher, but we recommend
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version 1.4 for optimal performance and access to features.
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PREREQUISITES
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In order to try this system you will need
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- The J2SE SDK, which can be downloaded for free from
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<http://java.sun.com/downloads/index.html>
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OR any other compatible Java implementation.
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- The Mercury distribution -- installed as usual. You can install
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from either the source or binary distribution.
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If you're reading this file from somewhere other than the
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Mercury distribution, try the Mercury homepage at
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<http://www.cs.mu.oz.au/mercury/>
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THE JAVA GRADE
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The Mercury compiler currently supports the grade 'java' to target Java
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bytecode. Support for building and installation of this grade
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is still somewhat rudimentary.
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To run a Mercury program using the java grade, you need to build the Mercury
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library and runtime in the java grade, using the Mercury source distribution.
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You will also need to set the environment variable CLASSPATH to include the
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mercury standard and runtime libraries for java, as well as the current
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directory. You should use a command of the form:
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CLASSPATH=<prefix>/mer_std.jar:<prefix>/mer_std.runtime.jar:.
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export CLASSPATH
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where <prefix> is the location of the installed jar files, which will probably
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be /usr/local/mercury/lib/mercury/lib/java or something similar.
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You can now build programs such as hello.m or calculator.m in the samples
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directory.
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cd samples
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mmc --make --grade java hello
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Now you can run hello
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./hello
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USING JAVA
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The Mercury standard library has not been fully ported to Java yet.
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The use of unimplemented procedures will result in a run-time error,
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with a message such as "Sorry, not implemented: foreign code for this
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function", and a stack trace.
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If you find missing functionality, you can interface to Java using Mercury's
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foreign language interface.
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For example:
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:- pred to_string(T::in, string::out) is det.
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:- pragma foreign_proc("Java", to_string(T::in, Str::out), [],
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"
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Str = T.toString();
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").
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The implementation will include this Java code in the module's .java file, and
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you can then call the predicate to_string exactly the same as if it were
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implemented using pure mercury code.
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For more information about the foreign language interface, see the Mercury
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Language Reference Manual, which you can find at:
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<http://www.cs.mu.oz.au/mercury/information/documentation.html>
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RESOURCES
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You might find the following pages useful:
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<http://www.cs.mu.oz.au/research/mercury/java.html>
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<http://java.sun.com/reference/api/index.html>
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<http://www.cs.mu.oz.au/mercury/information/documentation.html>
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FREQUENTLY ASKED QUESTIONS (FAQS)
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Q. What are the advantages of using the Java back-end?
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A. The main advantages are easy access to the wide range of libraries available
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for the J2SE platform, including web applet development, and the portability
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you get from using Java bytecode.
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Q. What version of Java should I be using?
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A. Java 2 Platform Standard Edition, version 1.2 or greater. Note that some
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features require version 1.4 or greater, however.
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Q. Which features?
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A. When using a Java version earlier than 1.4, there are limitations on treating
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stdin and stdout as binary files with respect to seeking. See the
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documentation for io.m in the standard library for more details.
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Q. What features are not yet implemented?
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A. The following standard library modules are completely unimplemented:
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benchmarking
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construct
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deconstruct
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store
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type_desc
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Type classes are not yet fully supported, nor are Mercury-level debugging
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and profiling for the Java back-end.
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Q. So how do I enable Java-level debugging?
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A. By default, javac already generates line number and source file debugging
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information. You can include local variable debugging information by
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specifying "--target-debug" when invoking the Mercury compiler, or by
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setting the JAVACFLAGS variable to include "-g" when invoking mmake,
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e.g.
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mmc --make --grade java --target-debug <progname>
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or
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mmake GRADE=java JAVACFLAGS=-g <progname>
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You can then use Sun's "jdb" debugging tool, which comes
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as part of the Java SDK distribution, to debug your program.
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For more information, see the documentation for javac and jdb.
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