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:

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