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From: broman@noscvax.UUCP
Newsgroups: net.lang.ada
Subject: Re: ForTran-Ada + flamette + question
Message-ID: <492@noscvax.UUCP>
Date: Wed, 21-May-86 12:40:37 EDT
Article-I.D.: noscvax.492
Posted: Wed May 21 12:40:37 1986
Date-Received: Sat, 24-May-86 05:01:44 EDT
References: <8605210805.AA20308@ucbvax.Berkeley.EDU>
Organization: Naval Ocean Systems Center, San Diego
Summary: map an enumeration to the procedures with a case statement.
List-Id: <comp.lang.ada>

In article <8605210805.AA20308@ucbvax.Berkeley.EDU>, larry@JPL-VLSI.ARPA writes:
> The biggest difference is that you can use subprogram names as parameters 
> to subprograms in ForTran and you can't in Ada.  This is causing me major
> problems in porting EMACS (written in C) to Ada.
> Anyone have an idea how to do run-time binding of keys to commands in Ada?

Unfortunately, Ada seems to be designed to make that as hard as possible.
The Steelman requirement 5D says: "Procedures, functions, types, labels,
exception situations, and statements shall not be assignable to variables,
be computable as values of expressions, or be usable as nongeneric parameters
to procedures or functions."  This is a major lossage, in my view, compared
to the reasonable design in (e.g.) Modula-2 for defining procedure pointers.

The only way I can see to simulate procedure pointers is to define an
enumeration type with elements corresponding to the procedures that may be
pointed to (as well as NULL) and write a procedure with a big CASE
statement which dispatches to the procedure corresponding to the
enumeration-value you supply as a parameter (or complains about calling NULL).

Yeah, I know, yuk.


Vincent Broman, code 632,  Naval Ocean Systems Center, San Diego, CA 92152, USA
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