Scheme - implementing basic OOP, having trouble properly setting up new()/this

Question

To learn the paradigm of OOP, we were asked to implement our own OOP language within scheme. I started by creating a single object, then a single class based off that object. My next step would be to create a 'class factory' as my professor calls it, a function that would create classes based off of a certain specification input. Before I can get to that though, I am facing what I think is a simple problem:

here is my class, it works:

(define pclass
  (λ input
    (let ((p-obj (list 'let `((xvar ,(caar input)) (yvar ,(cadar input)) (*this* null))
                       '(λ input
                          (let ((method (car input)) (args (cdr input)))
                            (cond
                              ((eq? 'display method) (begin
                                                       (display "Coords: x=") (display xvar) 
                                                       (display ", y=") (display yvar) (newline)))
                              ((eq? 'setx method) (set! xvar (cadr input)))
                              ((eq? 'getx method) xvar)
                              ((eq? 'gety method) yvar)
                              ((eq? 'polar method) (let ((radius (sqrt (+ (* xvar xvar) (* yvar yvar))))
                                                         (angle (/ (truncate (* (atan (/ yvar xvar)) 
                                                                            (/ 36000 (* 2 3.1415)))) 100))) 
                                                     (list radius angle)))
                              ((eq? 'dist method) (let ((x2 ((cadr input) 'getx)) 
                                                        (y2 ((cadr input) 'gety))) 
                                                    (sqrt (+ (expt (- x2 xvar) 2) (expt (- y2 yvar) 2)))))
                              ((and (eq? 'set method) (null? *this*)) (set! *this* (cadr input)))
                              (else (begin (display "Error: No method with signature: ") (display method)))
                           ))))))
      (eval p-obj))))

my problem is in my new function. If I run it this way:

(define new
  (λ input
    ((car input) (cdr input))))

it works just fine, aside from the issue of assigning my this variable. To assign it, I assume it is something like this:

(define new
  (λ input
    (let ((new-obj ((car input) (cdr input))))
      (new-obj 'set new-obj))))

but this method doesn't return a procedure object to assign when I run my code:

(define x (new pclass 3 5))

I am sure it is some small quirk of let that I don't fully understand. I should mention, if I define x with the first new code, it works fine and I can make method calls to x. I just don't have a this pointer for when I need it. I don't understand why the let block in my class returns a procedure object just fine, but the let block in my new function doesn't.

Answer 1

...fixed it.

...
((and (eq? 'set method) (null? *this*)) (begin (set! *this* (cadr input)) *this*))
...