Issue: PROCLAIM-SCOPE (Version 1)

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

As indicated in the discussion below, I think this is really a rough
cut, but I think the issue it treats is a real one so I figured I'd
see what others think.
 -kmp

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Issue:        PROCLAIM-SCOPE
References:   PROCLAIM (pp156-157)
Category:     ADDITION
Edit history: 26-Aug-88, Version 1 by Pitman
Status:	      For Internal Discussion

Problem Description:

  It would be useful to be able to do PROCLAIM without worrying about cleaning
  up afterward. For example, a file containing:

  In some cases, such as SPECIAL, there is no way to disable the effect of a
  proclamation.

  In other cases, such INLINE and SAFETY, it is possible but inconvenient to
  change the declaration later. Even so, there is no way of inquiring about the
  previous value in order to correctly restore it.

Proposal (PROCLAIM-SCOPE:ADD-KEYWORD-PERVASIVE):

  Introduce a :LOCALLY keyword parameter to PROCLAIM which controls
  the scope of a proclamation.

  (PROCLAIM proclamation :LOCALLY T)
    In a file, this would put the PROCLAMATION into effect for the entire
    rest of time during which the file was being loaded (including
    recursive loads).

    Interactively, it would be the same as :LOCALLY NIL.

  (PROCLAIM proclamation :LOCALLY NIL)
    In a file or interactively, this would put the PROCLAMATION into
    effect permanently. (The declaration would not be retracted when the
    file was done loading.)

Proposal (PROCLAIM-SCOPE:ADD-KEYWORD-NON-PERVASIVE):

  Introduce a :LOCALLY keyword parameter to PROCLAIM which controls
  the scope of a proclamation.

  (PROCLAIM proclamation :LOCALLY T)
    In a file, this would put the PROCLAMATION into effect for the entire
    rest of the current file. Recursive loads or compilations would rebind
    this to the global default.

    Interactively, this would affect interactive work but would not 
    affect the default for files loaded.

  (PROCLAIM proclamation :LOCALLY NIL)
    In a file or interactively, this would put the PROCLAMATION into
    effect permanently, affecting the default for files in which no
    local proclamation overrode it. (The declaration would not be retracted
    when the file was done loading.)

Test Case:

  Given a file "FOO" containing:

   (PROCLAIM '(OPTIMIZE (SPEED 0) (SAFETY 3)) :LOCALLY T)
   ...

  Doing

   (LOAD "FOO")

  would not clobber the global default for SPEED/SAFETY.

Rationale:

  This would address several existing problems with CL...
    - Declarations of optimize qualities such as speed/safety
    - Absence of UNSPECIAL declaration

  Macsyma has a lot of files which do (PROCLAIM '(SPECIAL ...)) at the
  top of the file and then does an implementation-specific
  (PROCLAIM '(UNSPECIAL ...)) at the bottom for implementations that
  support it. It would be both more modular and more portable to do
  something such as what is proposed here.

Current Practice:

  Symbolics Cloe binds optimization qualities (SAFETY, SPEED, 
  COMPILATION-SPEED) in file compilations and doesn't allow
  them to affect the global default.

Cost to Implementors:

  [I imagine the level of difficulty in providing this feature is in the
   low to intermediate difficulty range. It's not likely to be trivial for
   anyone, but I doubt anyone is going to claim that it is prohibitively
   expensive if we can get the details right and show that it satisfies a
   real need. -kmp]

Cost to Users:

  None. This is a compatible change.

Cost of Non-Adoption:

  Programmers would continue to clobber each others environments with pervasive
  SPEED and SAFETY proclamations.

Benefits:

  It would be possible to proclaim SPEED/SAFETY information locally in a file
  without worrying about the pervasive effect on other code compiled/loaded
  subsequently in the same environment.

Aesthetics:

  Probably people would find that this kind of flexibility had a beneficial
  effect on program aesthetics.

Discussion:

  Pitman has no firm opinion on this issue at this time, but believes that
  something like this might be quite useful if we could iron out the details.