Locate and position the current Audacity source code, and clear a variety of old junk out of the way into junk-branches

nyquist/evalenv.lsp

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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 ()
+  '(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)))
+