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Access to lexical environment?
Date: Sun, 8 Nov 87 21:12:26 EST
Creating new syntax using Lisp -- access to lexical environment?
I am not sure how to properly develop simple extensions to Lisp
syntax (using CL). For example, suppose that I'd like to set up a
way to create new things that has the following (familiar) syntax:
(def-newthing fred (other-thing) ((n :initform (+ a b))
(ls :initform (rest ls1)))
Now a,b, and ls1 would typically be lexically scoped. Given this, how
do I define "def-newthing"? If I use defun, it will attempt to
evaluate (other-thing), and worse, ((n :initform ....)). This won't
work. If I use defmacro, when I pull out an initform to evaluate, such
as (+ a b), the defmacro won't allow me access to the lexical bindings
of a and b. eval has similar problems. I'm stuck. Any ideas? (There
might be a lisp group to send this to, but we don't subscribe --
anyway, I have confidence that I'll be enlightened on this by sluggers.)
College of Computer Science 161CN
360 Huntington Ave.
Boston, MA 02115
I may be dense this morning (but after all, it is Monday), but I don't
see what's wrong with defmacro. So long as the :initform's aren't
evaluated by the macro expansion code, they will be in the correct
For a simple example.
(defmacro def-thing (foo bar)
`(defvar ,foo ,bar))
(let ((a 3))
(def-thing foo (+ a 5)))
will expand to
(let ((a 3))
(defvar foo (+ a 5)))
which is referencing `a' lexically.
The important thing is that the defmacro form can't eval its arguments
at expansion time and expect to be able to reference any lexical