; constructor to create a part with no subparts.
; called as (simple-part n) where n is the
; name of the part.

(define simple-part
  (lambda (s)
    (list 'simple-part s)))

; constructor to create a part with subparts
; called as (complex-part n l) where n is the
; name of the part and l is the list of its
; subparts.

(define complex-part
  (lambda (s l)
    (list 'complex-part s l)))

; test to determine whether a part has no subparts.

(define is-simple?
  (lambda (s)
    (eq? (car s) 'simple-part)))

; test to determine whether a part has subparts.

(define is-complex?
  (lambda (s)
    (eq? (car s) 'complex-part)))

; accessor function that returns the name of a part.

(define name-of
  (lambda (s)
    (car (cdr s))))

; accessor function that returns the list of all
; the subparts of a part.  if the part is simple,
; this returns the empty list.

(define parts-of
  (lambda (s)
    (if (is-simple? s)
        '()
        (car (cdr (cdr s))))))

; here is a simple example of how to use the constructors
; to create a representation of a whole that is made up
; of parts.

(define basic-doric-form
  (complex-part
   'doric-form
   (list (simple-part 'entablature)
         (simple-part 'column)
         (simple-part 'pedestal))))

; here is a complex example of how to use the constructors
; to create a representation of a whole that is made up of
; parts.

(define full-doric-form
  (complex-part
   'doric-form
   (list (complex-part
          'entablature
          (list
           (simple-part 'cornice)
           (simple-part 'frieze)
           (simple-part 'architrave)))
         (complex-part
          'column
          (list (complex-part
                 'capital
                 (list (complex-part
                        'abacus
                        (list (simple-part 'fillet)
                              (simple-part 'cymation)
                              (simple-part 'plinth)))
                       (complex-part 
                        'necking
                        (list (simple-part 'fillets)
                              (simple-part 'astragal)
                              (simple-part 'cincture)))))
                (simple-part 'shaft)
                (simple-part 'column-base)))
         (complex-part
          'pedestal
          (list (simple-part 'cap)
                (simple-part 'dado)
                (simple-part 'base))))))