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 somewhere
in the CLASSPATH.
You can also compile your Scheme program to native code using GCJ.