Re: Interface/Implementation (was Re: Design by Contract)

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Wes said

<<No. I mean both.  Untrue because IF the order in the body is
  changed, it is NOT due to compilation dependencies, AND "in an
  age of" modern tools (such as 'grep') there no reason for the
  order to make things hard to find.  Unpalatable, because one
  of Ada's lower priority goals was to make a one-pass compiler
  possible though not mandatory.>>

That's a bit misleading. It is in fact NOT possible in any reasonable
way to create a one-pass compiler for Ada 95, and certainly no one has
done so. The design goal is a rather different one, it is to enable a
basically one pass scan for human comprehension purposes. If you stick
to a basically linear elaboration model, you make it easier for the
reader.

    >   "Does the Ada95 standard impose dependency-related ordering?"

<<To some extent, as stated above.  But things declared in a legal
  order in the spec do not have to have their repetitions in the
  same order in the body.  (And let's not start about repetitions
  again.  We've already established either that this kind of
  repetition is not a problem, or that arguing about it will
  accomplish NOTHING.)>>


To clarify, in general there is no restriction on the order in which
subprograms occur. However, Ada follows the C and Pascal style of
basically forbidding forward references, rather than the Algol-68
style which allows forward references.

This is a very deliberate choice, and one I strongly support. Following
the Algol-60/68 choice here is a serious wrong step in my view (and
certainly mainstream language design agrees with this viewpoint).