Fwd: [Jscheme-user] jscheme and oop

[Timothy H. <tim...@ma...>]

> Hi Boris,
>
> On Sunday, March 9, 2003, at 12:55 AM, Boris Tschirschwitz wrote:
>> Hi.
>>
>> Assuming that my ignorance mostly stems from not having studied jscheme
>> long enough, I checked the list archives for answers,
> Thanks for checking first!
>
>> but I couldn't find
>> anything and the sf system seems to be really terrible.
> What made it so horrible? Response time, organization,...?
>
>>
>> I am wondering about the following: If I want to program using classes 
>> and
>> objects, do I have to make all my structures Java classes, 
>> objects, ...?
>> I wonder if this might restrict me in manipulating these objects in the
>> scheme way. Yes, this sounds very vague, b/c I am not absolutely sure 
>> what
>> I am asking and hope that someone on the list might understand it 
>> better
>> than I do.
>
> You should look at the webpage:
>       http://jscheme.sourceforge.net/jscheme/src/dclass/dclass.html
> which describes several approaches for working with Java classes from 
> Jscheme.
>
> In summary, the main approaches we've tried are:
>  * don't define any new classes (i.e. use Java as a library language), 
> e.g. see the jlib/Swing.scm library
>  * when this doesn't work, define a wrapper class that allows you to 
> dynamically
>     assign functionality to a Java class from Jscheme (e.g. see the 
> jlib/SchemeCanvas.java class)
>  * for an interface you can use the Proxy class to implement that 
> interface at runtime in Jscheme
>  * for a non-interface, you can use the dclass package to define Java 
> classes in Scheme
>     and compile them to Java, e.g. the weblink above gives an example 
> of defining a class
>     "Compare" in a package "frog". This example is in dclass/test.scm, 
> reproduced below:
>>
>>   (define-class
>>     (package frog)
>>     (import java.util.Comparator)
>>     (public class Compare implements Comparator)
>>     ;; Design issue, fields must be public for Jscheme code to access.
>>
>>     (public Procedure predicate)	
>>
>>     (public Compare (Procedure predicate)
>>      (.predicate$ this predicate))
>>
>>     (public boolean predicate (Object a Object b)
>>      ((.predicate$ this) a b))
>>
>>     (public int compare (Object a Object b)
>>      (cond ((.predicate this a b) -1)
>> 	   ((.predicate this b a) 1)
>> 	   (else 0)))
>>
>>     (public boolean equals (Object that)
>>      (and (eq? (.getClass this) (.getClass that))
>> 	  (eq? (.predicate$ this) (.predicate$ that))))
>>
>>     (public int hashCode () 0))
>>
>>
>
>
>     The following script shows how to run that example:
>
>> % java -cp lib/jscheme.jar:src jscheme.REPL
> Note:  we have to add a folder "src" to the classpath as dclass will 
> compile all new classes into
> this folder..
>>
>>
>> Jscheme 6.1.0 3/7/2003 http://jscheme.sourceforge.net
>>
>>
>> > (load "elf/basic.scm")
>> #t
>> > (load "dclass/dclass.scm")
>> #t
> At this point we have loaded in the dclass compiler...
> we are now ready to compile a new class, we could do this interactively
> by making a call to   > (define-class (package-frog) ....)
> But that can be error-prone...., so we load it in from a file....
>
>> > (load "dclass/test.scm")
> ; the compiler echoes the generated code to the console as well as to 
> the file
>> Writing Java code for frog.Compare to 
>> /Users/tim/Research/Software/jscheme/src/frog/Compare.java
>> // Generated by Jscheme by tim  on Sun Mar 09 04:16:20 EST 2003
>>  package frog;
>> import java.util.Comparator;
>> import jsint.Procedure;
>> import jscheme.JS;
>> public class Compare implements Comparator { public Procedure 
>> predicate;
>> public Compare(Procedure predicate) { JS.call(DCLASS_C_Compare0, this, 
>> predicate);
>> }
>> private static final Procedure DCLASS_C_Compare0 =(Procedure) 
>> JS.eval("(lambda (this predicate) (.predicate$ this predicate))");
>> public boolean predicate(Object a, Object b) { return 
>> JS.booleanValue(JS.call(DCLASS_M_I_predicate1, this, a, b));
>> }
>> private static final Procedure DCLASS_M_I_predicate1 =(Procedure) 
>> JS.eval("(lambda (this a b) ((.predicate$ this) a b))");
>> public int compare(Object a, Object b) { return 
>> JS.intValue(JS.call(DCLASS_M_I_compare2, this, a, b));
>> }
>> private static final Procedure DCLASS_M_I_compare2 =(Procedure) 
>> JS.eval("(lambda (this a b) (cond ((.predicate this a b) -1) 
>> ((.predicate this b a) 1) (else 0)))");
>> public boolean equals(Object that) { return 
>> JS.booleanValue(JS.call(DCLASS_M_I_equals3, this, that));
>> }
>> private static final Procedure DCLASS_M_I_equals3 =(Procedure) 
>> JS.eval("(lambda (this that) (and (eq? (.getClass this) (.getClass 
>> that)) (eq? (.predicate$ this) (.predicate$ that))))");
>> public int hashCode() { return 
>> JS.intValue(JS.call(DCLASS_M_I_hashCode4, this));
>> }
>> private static final Procedure DCLASS_M_I_hashCode4 =(Procedure) 
>> JS.eval("(lambda (this) 0)");
>> }
>> Compiling Java code for frog.Compare
> and it compiles the new code to src/from/Compare.class where it is 
> immediately available to us
>> #t
>>
> Next we use it to sort two arrays.... using two different comparators 
> c1 and c2
>> > (define c (frog.Compare. <))
>> frog.Compare@0
>> > (define arr #(1 4 2 5 6 79 3 4 8 5 3))
>> #(1 4 2 5 6 79 3 4 8 5 3)
>> > (Arrays.sort arr c)
>> #null
>> > arr
>> #(1 2 3 3 4 4 5 5 6 8 79)
>>
>> > (define c2 (frog.Compare. (lambda(x y) (or (< (first x) (first 
>> y)) (> (second x) (second y))))))
> .... this is a wierd sorting predicate, you can have A<B and B<A for 
> certain lists A,B, e.g. (1 5) and (4 6)
>> frog.Compare@0
>> > (define arr2 #((1 5) (4 3) (4 6) (5 3) (1 3) (1 6) (5 3) (5 4)))
>> #((1 5) (4 3) (4 6) (5 3) (1 3) (1 6) (5 3) (5 4))
>> > (Arrays.sort arr2 c2)
>> #null
>> > arr2
>> #((1 6) (1 5) (4 6) (1 3) (4 3) (5 4) (5 3) (5 3))
>>
>> > (exit)
>> #t
>> %
>>
>
> I hope this starts to answer your question...
>
>> Would it be beneficial to use something like Meroon?
> Perhaps, but then you may have to worry about interacting with two 
> object
> systems, Java's and Meroon's. I haven't tried to get Meroon working in
> Jscheme and it might be interesting!
>
> Best,
> ---Tim---
>