A lambda question

[Kent M Pitman <KMP@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: Tue, 26 Jul 88 20:20:57 EDT
    From: Scott.Fahlman@B.GP.CS.CMU.EDU

	If there were to be such a function, what would be a 
	good name for it?
    
    How about EXTRACT-LAMBDA-EXPRESSION ?

The T language provides such a primitive. It is called DISCLOSE
(named for symmetry with the ENCLOSE primitive which occurs in some
Scheme dialects and coerces a lambda expression into a procedure).
DISCLOSE may be overly generic-sounding for CL use, but I recommend
DISCLOSE-DEFINITION.

    I assume that the proposal will allow this function to return NIL if
    the original lambda expression has been compiled or optimized to the
    point where it can no longer be retrieved?  I wouldn't want to require
    memory-tight implementations to keep around the original form in all
    cases.

Since some applications for DISCLOSE have semantic impact, I don't agree
that it should be possible for an implementation to simply throw away
the information. I believe that we should spell out particular cases
in which it is or is not permissible. My personal preferences follow:

 - No compiler should be required to retain the source code
   when using the file compiler. That is, using COMPILE-FILE
   does not make the definition available in the environment into
   which the definitions are subsequently LOADed.

 - I am agnostic about interactive DEFUN, etc. I am content to see
   this information retained only at the discretion of the 
   interpreter.

 - I would prefer that arguments to COMPILE be retained, and possibly
   defuns done by explicit EVAL as well. The reason for this is that
   programs like Macsyma which have need of this function do not just
   go around peeking into arbitrary functions (in my experience). They
   usually want to peek into functions that they themselves instantiated.
   So primitives that allow explicit runtime instantiation of functions
   on a case-by-case basis should be reliably invertible (in my opinion).

Notes:

 - I would be ammenable to permitting this function to be SETF-able,
   so that people could ``NIL out'' definitions they didn't want to
   retain.

 - I would also be ammenable to having a special argument to COMPILE
   saying that the information must be retained. I don't care what
   the default value was.

 - If there is not any reliable situation in which a definition will
   have this information retained, then all the uses I have ever had
   for this except for pretty printing are nullified. Perhaps the
   pretty printing argument is reason enough to have it, though.

 - There is some question about whether in the case of named objects,
   (DEFUN FOO (X) X)
   (DISCLOSE-DEFINITION #'FOO) => (LAMBDA (X) X) or (DEFUN FOO (X) X)?
   I think the latter.
   Does whether FOO is still fdefined matter? I think not.