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Re: calling scheme procedure from java and passing a list as argument...


finally i understand my error,result of many years without coding in java...

here is the solution:

    LList glst = new LList();
    //glst = glst.list2(2,3); // works also
    glst = LList.list2(2,3);
    System.out.println("glst : "+glst);
    Object result0 = vec.plus(glst);
    System.out.println("result0 :"+result0);


    Pair pair = new Pair(2, LList.Empty);
    Pair pair2 = new Pair(3, pair);
    LList glst2 = new LList();
    glst2 = pair2;
    System.out.println("glst2 : "+glst2);
    Object result = vec.plus(glst2);
    System.out.println("result : "+result);

and the result:

glst : (2 3)
result0 :5
glst2 : (3 2)
result : 5

Le 18/09/2015 11:52, Damien Mattei a Ãcrit :
>
> Le 17/09/2015 20:54, Per Bothner a Ãcrit :
>>
>> On 09/17/2015 06:09 AM, Damien Mattei wrote:
>>> hello again,
>>> suppose i have a java code (the case is running on tomcat web server but
>>> that's make no difference)
>>> and i want to pass a list to a scheme routine, i have two questions:
>>> -is there a way to call a scheme procedure in kawa,i suppose the answer
>>> is yes but how?
>>> ( i know i can do it making a method in a kawa class definition and call
>>> the method)
>> This page talks about *evaluating* Scheme from Java:
>>
>> http://www.gnu.org/software/kawa/Evaluating-Scheme-expressions-from-Java.html
>>
>>
>> If you have a Scheme Proecdure object you can call by using one of the
>> apply methods.  For example:
>>
>>    Object[] args = {x, y};
>>    Object result = myProc.applyN(args);
>> or:
>>   Object result = myProc.apply2(x, y);
>>
>>> - but how can i pass a list as parameter, what is the equivalent of
>>> scheme list in java or kawa??
>>> I would greatly appre"ciate a little example...
>> To create a list you can use one of the static methods in
>> gnu..lists.LList,
>> like makeList or list1 ... list4.
>>
>> It's usually best to do as much as you can in Scheme: It is easier (and
>> better documented with a more stable API) calling Java from Scheme
>> than calling Scheme from Java.
> unfortunalely this is a java project including scheme,not the reverse,
> i tried to use list2 in this example but it complains that
> gnu.lists.LList is not a pair,
> in scheme a list is a pair.
> i have this error:
> Exception in thread "main" Argument #1 '(. #<not a pair>)' to 'car' has
> wrong type (gnu.lists.LList) (gnu.lists.LList cannot be cast to
> gnu.lists.Pair)
>         at Vector2D.plus(Vector2D.scm:28)
>         at helloworld.main(helloworld.java:30)
> Caused by: java.lang.ClassCastException: gnu.lists.LList cannot be cast
> to gnu.lists.Pair
>         ... 2 more
> when i try to run this code:
>
>     LList glst = new LList();
>     glst.list2(2,3);
>     Object result = vec.plus(glst);
>
> on this method definition in Vector2D class:
> ((plus L) ::int
>    (+ (car L) (cadr L)))
>
> this is of course for testing before doing serious work...
>
>
>
>


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