Using Scheme from Java

Using Scheme from Java is straight forward, though the API has been evolving. You can use the class silk.Scheme to provide a read-eval-print loop which is good for development. However, in your real applcation you might like to hid the fact that you are using Scheme. This can be done by:

• Construct a silk.Scheme object, scheme.
• Load Scheme definitions using one of the variations on scheme.load().
• Provide callbacks from Java ino Scheme by writing a Java class that accepts a Scheme Procedure, proc, as an argument and invokes that procedure on a list of arguments using Scheme.apply(proc, args) in an appropriate Java method.
• Argument lists can be constructed using SchemeUtils.cons() or SchemeUils.list(). Lists can be destructed using SchemeUtils.first() and SchemeUtils.rest().

For example, you can define an action listener that will invoke a Scheme procedure:

public class SchemeActionListener extends silk.SchemeUtils 
  implements java.awt.event.ActionListener {
  Procedure p;

  SchemeActionListener(Procedure p) { this.p = p; }
  public void actionPerformed(java.awt.event.Actionevent e) {
    Scheme.apply(p, cons(e, null)); }
}

You can then invoke it from Scheme using.

(import "SchemeActionListener")
(import "javax.swing.JButton")
(define button (Jbutton "press me"))
(add button (SchemeActionListener (lambda (e) (display e))))

From Java, you can also add a known global function, fred, as a call back using:

  Scheme.apply(scheme.getGlobal("fred"), args);