[plt-scheme] Problems with class definition

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I would like to define a matrix class, the syntax check is okay, but the
object doesn't understand the rows method. Could anyone tell me
what's wrong with the definition.

Harald

(define matrix<%> (interface () rows))

(define matrix%
   (class* object% (matrix<%>)

     (init-field (rows-size 0) (cols-size 0))

     (define/public rows
       (case-lambda
         ((new-rows-size) (set! rows-size new-rows-size))
         (() (rows-size))))

     (super-instantiate ())))

(define m (instantiate matrix% ()))
(send rows m)

Welcome to DrScheme, version 202.
Language: Pretty Big (includes MrEd and Advanced) custom.
reference to undefined identifier: rows
 > 

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