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;;
;; The EVAL function in the original XLISP evaluated in the current lexical
;; context. This was changed to evaluate in the NIL (global) context to
;; match Common Lisp. But this created a problem: how do you EVAL an
;; expression in the current lexical context?
;;
;; The answer is you can use the evalhook facility. The evalhook function
;; will evaluate an expression using an environment given to it as an
;; argument. But then the problem is "how do you get the current
;; environment?" Well the getenv macro, below obtains the environent by
;; using an *evalhook* form.
;;
;; The following two macros do the job. Insteading of executing (eval <expr>)
;; just execute (eval-env <expr>). If you want, you can dispense with the
;; macros and execute:
;;
;;(evalhook <expr> nil nil (let ((*evalhook* (lambda (x env) env)))
;; (eval nil)))
;;
;; Tom Almy 10/91
;;
(defmacro getenv ()
'(let ((*evalhook* (lambda (x env) env)))
(eval nil))) ; hook function evaluates by returning
; environment
(defmacro eval-env (arg) ; evaluate in current environment
`(evalhook ,arg nil nil (getenv)))
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