Space Station Lambda

;;; Replace the definition of NAME with a function that binds NAME's
;;; arguments to a variable named ARG-LIST, binds name's definition
;;; to a variable named BASIC-DEFINITION, and evaluates BODY in that
;;; context. TYPE is whatever you would like to associate with this
;;; encapsulation for identification in case you need multiple
;;; encapsulations of the same name.
(defun encapsulate (name type body)
  (let ((fdefn (fdefinition-object name nil)))
    (unless (and fdefn (fdefn-fun fdefn))
      (error 'undefined-function :name name))
    ;; We must bind and close over INFO. Consider the case where we
    ;; encapsulate (the second) an encapsulated (the first)
    ;; definition, and later someone unencapsulates the encapsulated
    ;; (first) definition. We don't want our encapsulation (second) to
    ;; bind basic-definition to the encapsulated (first) definition
    ;; when it no longer exists. When unencapsulating, we make sure to
    ;; clobber the appropriate INFO structure to allow
    ;; basic-definition to be bound to the next definition instead of
    ;; an encapsulation that no longer exists.
    (let ((info (make-encapsulation-info type (fdefn-fun fdefn))))
      (setf (fdefn-fun fdefn)
            (named-lambda encapsulation (&rest arg-list)
              (declare (special arg-list))
              (let ((basic-definition (encapsulation-info-definition info)))
                (declare (special basic-definition))
                (eval body)))))))

CL-USER(19): (defun gorm (x) (1+ x))
GORM
 
CL-USER(20): (SB-INT:ENCAPSULATE 'gorm 'identity '(apply sb-int:basic-definition sb-int:arg-list))
 
#<closure (SB-C::&OPTIONAL-DISPATCH SB-IMPL::ENCAPSULATION) {ACE428D}>
CL-USER(21): (gorm 10)
11
 
CL-USER(22): (SB-INT:ENCAPSULATE 'gorm 'add-five '(+ 5 (apply sb-int:basic-definition sb-int:arg-list)))
#</closure><closure (SB-C::&OPTIONAL-DISPATCH SB-IMPL::ENCAPSULATION) {ACEE31D}>
 
CL-USER(23): (gorm 10)
16
 
CL-USER(24): (SB-INT:ENCAPSULATE 'gorm 'add-seven '(+ 7 (apply sb-int:basic-definition sb-int:arg-list)))
 
#</closure><closure (SB-C::&OPTIONAL-DISPATCH SB-IMPL::ENCAPSULATION) {ACF84ED}>
CL-USER(25): (gorm)
23
</closure>

CL-USER(26): (SB-INT:UNENCAPSULATE 'gorm 'add-five)
T
 
CL-USER(27): (gorm 10)
18
 
CL-USER(28): (SB-INT:UNENCAPSULATE 'gorm 'add-seven)
T
 
CL-USER(29): (gorm 10)
11