Re: Ada to 'C' parameter passing problem

[Simon Wright <simon@pushface.org>]

rod.chapman@praxis-cs.co.uk (Rod Chapman) writes:

> mheaney@on2.com (Matthew Heaney) wrote in message news:> That Ada doesn't allow you to specify inout mode for function
> > parameters is a deficiency of Ada...
> 
> Wow!  This reflects somewhat of a gulf between our respective
> views of language design!  (Don't get me wrong, neither position
> is necessarily right or wrong, just different...)
> 
> At the SPARK end of the spectrum functions calls are expressions
> which return a value and never have a side-effect.  Procedure
> calls are statements which have side-effects - A rather
> significant _semantic_ difference!

I recall Robert Dewar saying that he thought that restricting
functions to "in" (or access) parameters was a Bad Idea -- Ada is a
programming language, not a mathematical abstraction, and there is
nothing in Ada to stop a function modifying global state. (Praise be,
say I). But Robert got outvoted during the Ada 9X process.

There would be nothing to stop SPARK requiring functions to have only
"in" parameters -- after all you disallow access parameters &
modifying global state!