EVAL

[mike%acorn@mit-live-oak.arpa]

    Date: Sat, 22 Nov 86 17:32 EST
    From: Alan Bawden <Alan@AI.AI.MIT.EDU>
    
        Date: Thu, 20 Nov 1986  16:19 EST
        From: "Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>
        EVAL cannot easily be defined to work in the lexical environment in
        which it appears because that lexical environment is not around at
        runtime,....

    Right.  This demonstrates that LEXICAL-EVAL would have to be a new special
    form, rather than simply a function.

This same issue seems to come up over and over. Will someone tell
me what is wrong with the following argument:
    
I see no reason for "lexical-eval" or any eval with an environment arg.
The following is a trivial source-to-source you can use to get the 
effect of a lexical eval:

Suppose you wanted

(defun foo (s-exp)  
  (let ((x 5))
   (flet ((bar (y) (+ x y)))
    (block here
     (tagbody :there
        (lexical-eval s-exp))))))

this is exactly equivalent to:

(defun foo (s-exp)  
 (eval
 `(let ((x 5))
   (flet ((bar (y) (+ x y)))
    (block here
     (tagbody :there
       ,s-exp))))))

which does not use any "lexical-eval". Since the primary 
effect of the compiler is to eliminate lexical environments, any
lexical "stuff" surrounding a call to "lexical-eval" can't really
be compiled (not much anyway) since it all might be referred to
by the s-expression being evaled. This being the case, the
second form here, which just eval's the entire lexical scope,
is roughly as efficient. 

...mike beckerle
Gold Hill Computers.