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From: Brian Drummond <brian@shapes.demon.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: What would you like in Ada202X?
Date: Sat, 30 Jun 2012 12:00:13 +0000 (UTC)
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Date: 2012-06-30T12:00:13+00:00
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On Wed, 25 Apr 2012 00:47:06 -0700, Martin wrote:

> Ok, we don't officially have Ada2012 yet but as no new features are
> going to be added to it, now seems like a good time to start thinking
> about the next revision.
> 
> My starters for 10 are:
> 
> 1) 1st class functions / lambdas 2) parallel loops / functions 3)
> Multiple dispatch
> 
> -- Martin

We can overload existing operators (+,-,etc)
But we can't define new ones, e.g. // to denote the value of electronic 
components connected in a parallel circuit) or -- (bad choice! maybe ++) 
for series connection. 

For example, the definition of // would clearly be different for 
resistance and capacitance, which we can assume to be distinct types of 
complex number.

The last language I used that allowed this, (Lingo, on the Linn Rekursiv) 
restricted the characters used to build such an operator to a suitable 
set, chosen to avoid clashes with the inherent language syntax, so no 
{ or } for example. 

One obvious problem with an extensible set of operators, in an operator 
precedence grammar, is assigning the precedence level of new operators.
Lingo resolved that dilemma by assigning the same precedence to all 
operators! You explicitly wrote a + (b*c) - d to achieve the usual 
precedence. Simple, clean, and effective, but entirely inappropriate for 
Ada!

Given that ways can be found to assign precedence to new operators, why 
are extensible operators not found in more languages that allow 
overloading? It would seem to be a useful way to add expressibility, and 
I can't see any fundamental drawbacks. 

If the demand is not there, is that because it has been considered and 
rejected, or is it simply below everyone's radar?

- Brian