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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Subscript brackets
Date: 1996/05/01
Message-ID: <EACHUS.96May1170359@spectre.mitre.org>#1/1
X-Deja-AN: 152461723
references: <4m515d$pok@calypso.bns.com.au>
organization: The Mitre Corp., Bedford, MA.
newsgroups: comp.lang.ada
Date: 1996-05-01T00:00:00+00:00
List-Id: <comp.lang.ada>



In article <4m515d$pok@calypso.bns.com.au> mike@calypso.bns.com.au (Michael Talbot-Wilson) writes:

  > Are there any plans to convert from parentheses to square brackets
  > for array subscripts in Ada?

   Not in this millenium....

  > Maybe this is a minor point, and I guess BASIC, PL/I and FORTRAN
  > programmers think it's better as it is.  (And I guess the use of
  > parentheses reflects that Ada's heritage is in those languages.)

   No, it reflects a unification between tabular data and functions
which is totally intentional.  I often prototype with many complex
options being tables in the prototype, and functions in the final
product:

    type Message_Length is array (Message_Type) of Integer;
     ...
    
    function Message_Length(M: in Message_Type) return Integer;

    This allows the message lengths to be changed in a table without
recompiling things.

  > But C, Pascal, Modula-2 and (if there are any left alive) ALGOL
  > programmers feel the reverse.  Minor or not, it is a big psycho-
  > logical hurdle to adjust to something inferior (and even the FAQ
  > concedes that this is a broken feature) in the name of doing
  > things better.

  > A preprocessor which converted just these parentheses to brackets
  > and left non-array-subscript parentheses alone would allow
  > existing source to be compiled.  And (I guess) remove the ambiguities
  > of parsing this feature from the compiler, allowing its cost to
  > be more clearly seen.

   I have a better idea...write a preprocessor to replace square
brackets with angle brackets, and you will have no problem using
existing Ada compilers.  I could probably write a very good
preprocessor of this form in a couple hours.

   However, if you decide to do realistic error checking, you have a
lot of decisions to make.  Do all attributes use parentheses, or just
those which are functions?  If A'First[1] requires brackets, what
about A'Range(1)?  You get the picutre.

  > It there any intention of doing this?  Is there any suggested date
  > when it might happen?  I think some people who would like to convert
  > to or start working in Ada would like a date to aim at, supposing it
  > is ever going to happen.

  I doubt it.  It could be done, but it would be a rough haul for very
little gain.


    
--

					Robert I. Eachus

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