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From: murthy@magnus.ircc.ohio-state.edu (Murthy S Gandikota)
Newsgroups: comp.lang.lisp
Subject: Question about INTERN
Message-ID: <1991Jan29.055536.1523@magnus.ircc.ohio-state.edu>
Date: 29 Jan 91 05:55:36 GMT
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consider the following lisp definitions:

(defstruct house
	rooms
	area)

(setf my-house (make-house :rooms 4 :area 100))

(setf any-house my-house)

(defun get-slot-value (obj slot)
;;this function returns the value of the slot in obj
(PROG (obj1 value)
	(setf obj1 obj)
	(if (equal (type-of obj) 'symbol) (setf obj1 (eval obj)))
	(setf value (eval `(,(intern (format nil "~a-~a" (type-of obj1) slot)) 
		,obj)))
	(RETURN value)))


(defun put-slot-value (obj slot value)
;;this function over writes the value of a slot
(PROG (obj1)
(setf obj1 obj)
(if (equal (type-of obj) 'symbol) (setf obj1 (eval obj)))
(eval `(setf (,(intern (format nil "~a-~a" (type-of obj1)) slot)) ,obj) 
	',value))))

(get-slot-value any-house 'rooms) returns 4

whereas

(get-slot-value my-house 'rooms) causes error

put-slot-value also behaves similarly

These functions used to work all right on Symbolics lisp. The errors
 only happen on Vax lisp 3.x!

Can anyone point out the reason? Or, point out other efficient ways to 
implement such functions? 


Thanks

Murthy Gandikota