Issue: ROOM-DEFAULT-ARGUMENT (Version 1)

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

Issue:        ROOM-DEFAULT-ARGUMENT
References:   ROOM (p442)
Category:     ADDITION
Edit history: 12-Sep-88, Version 1 by Pitman
Status:	      For Internal Discussion

Problem Description:

  Passing no argument to ROOM is not equivalent to any argument which
  can be passed. This makes data-flow from another function which wants
  to call ROOM inconvenient. Rather than simply passing a value through,
  the correct calling sequence must be selected as well. For example,
  one might have to do something like
  (CASE FLAG
    (:DEFAULT (ROOM))
    ((T NIL) (ROOM FLAG)))
  where (ROOM FLAG) would suffice

Proposal (ROOM-DEFAULT-ARGUMENT:NEW-VALUE):

  Specify that passing an argument of :DEFAULT is equivalent to passing
  no argument to ROOM.

Test Case:

  (ROOM :DEFAULT) is functionally equivalent to (ROOM).

Rationale:

  Minimal change needed to get around the stated problem.

  Allows ROOM to be describable without reference to supplied-p
  information.

Current Practice:

  Symbolics Genera defines ROOM using &REST and looks for NIL, (T), or (NIL).
  [This reduces its ability to do compile-time number-of-argument checking.]

  Some other implementations probably have a magic undocumented value
  to avoid use of a SUPPLIED-P argument.

Cost to Implementors:

  Probably it involves negligible resources to change this.
  In most implementations, the resulting code would probably look better.

Cost to Users:

  None. This change is upward compatible.

Cost of Non-Adoption:

  The description of ROOM will look yucky in the emerging specification.
  The source code for ROOM will look yucky.
  [How's that for objective? -kmp]
  Error checking in some implementations may be sub-optimal.

Benefits:

  The description of ROOM in the now-being-written specification would
  be less complicated.

Aesthetics:

  This proposal would make a minor improvement in aesthetics.

Discussion:

  This is obviously a low-priority issue, but would require such little
  resources to fix that it seems worth doing.

  Pitman supports this addition.

  It's perhaps too bad that keywords like :SHORT, :MEDIUM, and :LONG
  weren't chosen instead of T and NIL, since T and NIL have a bit of a
  binary feel to them and it's hard to think of a good name for the
  default case.