Function Definitions in Static Modules

[David O'Callaghan <david dot ocallaghan at cs dot tcd dot ie>]

Hi,

I'm having some trouble using static modules from Java. I have a set of 
test cases, attached.

Here's the Kawa Scheme code for the module:

(define (f x) (+ 1 x))

(define (make-adder i) (lambda (x) (+ i x)))

(define g (make-adder 1))

(define (h x) (g x))

I can call all the functions if the module is imported into a scheme 
program with require [test-def-req.scm in attachment]. However, if I try 
to invoke the static methods g or h from Java or from Scheme problems 
arise. Firstly, g is not exported as a method; I can guess why. Second, 
invoking h gives a null pointer exception when it tries to invoke g; I 
find this harder to accept. For example, in [TestDefMainBroken.java]:

  System.out.println("(h 41) -> " + TestDefModule.h(41));

will lead to a NullPointerException.

Similarly, with this Kawa code [test-def-stat-broken.scm]:

  (display (format "(invoke-static <TestDefModule> 'h 41) -> ~A\n"
                   (invoke-static <TestDefModule> 'h 41)))

I get a NullPointerException:

  java.lang.NullPointerException
        at TestDefModule.h(test-def.scm:13)
        at TestDefStatBroken.run(test-def-stat-broken.scm:8)
        at gnu.expr.ModuleBody.run(ModuleBody.java:44)
        at gnu.expr.ModuleBody.run(ModuleBody.java:32)
        at gnu.expr.ModuleBody.runAsMain(ModuleBody.java:132)
        at TestDefStatBroken.main(test-def-stat-broken.scm)

I found that I could fix the scheme case by adding (require 
<TestDefModule>) [see test-def-stat.scm]. I wasn't sure what the 
equivalent was in Java, but I eventually found that this fixes the 
probem [TestDefMain.java]:

        TestDefModule td = new TestDefModule();
        td.run();

I then tried to port the fix from my test case back to my real code and 
ran into a related problem: I have a static module that is used by a 
class created with define-simple-class, which in turn is used by a Java 
class. I found it necessary to add a non-default constructor to my 
define-simple-class in order to initialise the module. For the test case 
[see test-def-class.scm] I need:

    ((*init*) (invoke (make <TestDefModule>) 'run))

My question is this: is it always necessary to invoke the run method on 
a static module for functions like h to work, or am I doing something wrong?

Thanks,

David

Attachment: test-def.tar.gz
Description: GNU Zip compressed data