#

## Issue DO-SYMBOLS-BLOCK-SCOPE Writeup

    Issue:             DO-SYMBOLS-BLOCK-SCOPE
    References:        DO-SYMBOLS, DO-EXTERNAL-SYMBOLS, DO-ALL-SYMBOLS
    Related issues:
    Category:          CLARIFICATION
    Edit history:      v1, 13 Feb 1991, Sandra Loosemore

    Problem description:

      It's not clear what the scope of the implicit NIL block surrounding
      a DO-SYMBOLS, DO-EXTERNAL-SYMBOLS, or DO-ALL-SYMBOLS form is.  Does
      it include only the body forms or the entire form?

    Proposal (DO-SYMBOLS-BLOCK-SCOPE:ENTIRE-FORM):

      Clarify that the implicit NIL block effectively surrounds the entire
      DO-SYMBOLS, DO-EXTERNAL-SYMBOLS, or DO-ALL-SYMBOLS form.

    Rationale:

      This is consistent with DO, DO*, DOLIST, and DOTIMES.

    Examples:

      (block nil
          (do-symbols (s (or (find-package "FROB") (return nil)))
              (print s))
          t)

      => always returns T since BLOCK referred to by the RETURN is the
         implicit BLOCK established by DO-SYMBOLS, not the explicit outer
         BLOCK.

    Current Practice:

      Lucid version 4.0 implements this proposal.
      Allegro version 3.1 implements DO-EXTERNAL-SYMBOLS and DO-ALL-SYMBOLS
      according to this proposal, but not DO-SYMBOLS.
      Chestnut's Lisp-to-C translator implements this proposal.

    Cost to Implementors:

      Small.

    Cost to Users:

      None.

    Cost of non-adoption:

      Implementations will differ and the language specification will be vague,
      without any good reason.

    Performance impact:

      Probably none.

    Benefits:

      The cost of non-adoption is avoided.

    Esthetics:

      Making the language consistent is a good thing.

    Discussion:
    -------

Copyright 1996-2001, Xanalys Inc. All rights reserved.