Evaluating Scheme expressions from Java
The following methods are recommended if you need to evaluate a
Scheme expression from a Java method.
(Some details (such as the ‘throws’ lists) may change.)
Static method: void Scheme.registerEnvironment ()
Initializes the Scheme environment. Maybe needed if you
try to load a module compiled from a Scheme source file.
Static method: Object Scheme.eval (InPort portenv
Read expressions from port, and evaluate them in the
env environment, until end-of-file is reached.
Return the value of the last expression,
or Interpreter.voidObject if there is no expression.
Static method: Object Scheme.eval (String stringenv
Read expressions from string, and evaluate them in the
env environment, until the end of the string is reached.
Return the value of the last expression,
or Interpreter.voidObject if there is no expression.
Static method: Object Scheme.eval (Object sexprenv
The sexpr is an S-expression (as may be returned by read).
Evaluate it in the env environment, and return the result.
For the Environment in most cases you could use
‘Environment.current()’. Before you start, you
need to initialize the global environment,
which you can do with
Environment.setCurrent(new Scheme().getEnvironment());
Alternatively, rather than setting the global environment,
you can use this style:
Scheme scm = new Scheme();
Object x = scm.eval("(+ 3 2)");
System.out.println(x);
Using javax.script portable Java scripting
Kawa also supports the standard
javax.script API.
The main advantage of this API is if you want your users to be able to choose
between multiple scripting languages. That way you can support Kawa
without Kawa-specific programming.
For example the standard JDK tool jrunscript provides a
read-eval-print-loop for any language that implements the javax.script
API. It knows nothing about Kawa but can still use it:
$ jrunscript -cp kawa.jar -l scheme
scheme> (cadr '(3 4 5))
4
(Of course the jrunscript REPL isn’t as nice as the one that
Kawa provides. For example the latter can handle multi-line inputs.)
