Issue ROOM-DEFAULT-ARGUMENT Writeup

Issue:        ROOM-DEFAULT-ARGUMENT

References:   ROOM (p442)

Category:     ADDITION

Edit history: 12-Sep-88, Version 1 by Pitman


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.