blob: 155139f5d2da6f70421969c64e715d9ecbaea83e (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
|
;;
;; 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 ()
'(progv '(*evalhook*)
(list #'(lambda (exp env) env))
(eval nil)))
; this didn't work, may be for a later (Almy) version of xlisp?
;(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)))
|
