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Date: 15 Jan 92 06:04:54 GMT
From: csus.edu!wupost!zaphod.mps.ohio-state.edu!mips!cs.uoregon.edu!nntp.uorego
n.edu!milton!mfeldman@ucdavis.ucdavis.edu  (Michael Feldman)
Subject: Re: Ada statement
Message-ID: <1992Jan15.060454.16683@milton.u.washington.edu>
List-Id: <comp.lang.ada>

In article <1992Jan14.031331.18320@cs.rose-hulman.edu> eigenstr@zoe.cs.rose-hul
man.edu (Todd R. Eigenschink) writes:

  [ stuff deleted ]
>
>	Why the HELL is there the NULL statement?????????????
>
>There's only one use as far as I can tell...to fill an empty procedure/
>function declaration so that the body isn't empty.  So why not just allow
>an empty body?
>
NULL can be useful in e.g. a CASE statement, which requires that all
values of the case variable be accounted for.

WHEN OTHERS => NULL;

is often handy to write if no action is needed.
The NULL statement is similar to "THIS PAGE IS INTENTIONALLY LEFT BLANK"
in documents - it indicates a DELIBERATE "leaving out" of something.

Empty bodies are confusing; they lead to endless grief in C.
Consider
  x = 1;
  while (x < 100);
  {
     x++
  }

This is an endless loop, because the carelessly placed semicolon after
the while clause creates an empty loop body. This can't happen in Ada.

Mike

-------------------------------------------------------------------------------
Michael B. Feldman                       co-chair, SIGAda Education Committee

Visiting Professor 1991-92               Professor
Dept. of Comp. Sci. and Engrg.           Dept. of Elect. Engrg. and Comp. Sci.
University of Washington FR-35           The George Washington University
Seattle, WA 98105                        Washington, DC 20052

mfeldman@cs.washington.edu               mfeldman@seas.gwu.edu
(206) 632-3794 (voice)                   (202) 994-5253 (voice)
(206) 543-2969 (fax)                     (202) 994-5296 (fax)
-------------------------------------------------------------------------------