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All Scheme functions and source files are invisibly compiled into internal Java byte-codes. A traditional evaluator is only used for top-level directly entered expressions outside a lambda. (It would have been simpler to also byte-compile top-level expressions by surrounding them by a dummy lambda. However, this would create a new Class object in the Java VM for every top-level expression. This is undesirable unless you have a VM that can garbage collect Class objects.)
To save speed when loading large Scheme source files, you probably want to pre-compile them and save them on your local disk. There are two ways to do this.
You can compile a Scheme source file to a single archive file.
You do this using the compile-file
function.
The result is a single file that you can move around and load
just like the .scm
source file. You just specify the name
of the archive file to the load
procedure.
Currently, the archive is a "zip" archive and has extension ".zip";
a future release will probably use "Java Archive" (jar) files.
The advantage of compiling to an archive is that it is simple
and transparent. A minor disadvantage is that it causes the
Java "verifier" to be run when functions are loaded from it,
which takes a little extra time.
Alternatively, you can compile a Scheme source file to a
collection of `.class' files.
You then use the standard Java class loading mechanism to load the code.
The Java "verifier" does not need to get run, which makes
loading a little faster.
The compiled class files do have to be installed be installed somewhere
in the CLASSPATH
.
To byte-compile a file `foo.scm' do:
(compile-file "foo.scm" "foo")
This will create `foo.zip', which contains byte-compiled "j-code" that implements `foo.scm'.
You can later do:
(load "foo")
This will load `foo.zip', which should have the same effect as loading `foo.scm', except you will get the byte-compiled versions.
Invoking `kawa' (or `java kawa.repl') with the `-C' flag will compile a `.scm' source file into one or more `.class' files.
You run it as follows:
kawa [-d outdirectory] [-P prefix] [-T topname] [--main] -C infile
Note the `-C' must come last, because `Kawa' processes the arguments and options in order,
Here:
main
method so that the resulting "top" class can
be used as a stand-alone application. See section Compiling Scheme to a standalone application.
When you actually want to load the classes, the outdirectory
must be in your `CLASSPATH'.
You can use the standard load
function to load the code,
by specifying the top-level class, either as a file name
(relative to outdirectory) or a class name.
E.g. if you did:
kawa -d /usr/local/share/java -P my.lib. -T foo -C foosrc.scm
you can use either:
(load "my.lib.foo")
or:
(load "my/lib/foo.class")
If you are compiling a Scheme source file (say `foosrc.scm') that uses macros defined in some other file (say `macs.scm'), you need to make sure the definitions are visible to the compiler. One way to do that is with the `-f':
kawa -f macs.scm -C foosrc.scm
A Java application is a Java class with a special method
(whose name is main
). The application can be invoked directly
by naming it in the Java command.
If you want to generate an application from a Scheme program,
create a Scheme source file with the definitions you need, plus
the top-level actions that you want the application to execute.
You can compile in the regular way decribed in the previous section, but add
the --main
option. For example,
assuming your Scheme file is MyProgram.scm
:
kawa --main -C MyProgram.scm
This will create a MyProgram.class
which you can either load
(as decribed in the previous section), or invoke as an application:
java MyProgram [args]
Your Scheme program can access the command-line arguments args by using the global variable `command-line-arguments'.
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