Re: Why is Ada NOT a good choice for a beginner to programming?

Re: Why is Ada NOT a good choice for a beginner to programming?

[Grein, Christoph]

> > One complaint he had was that it be possible to define a Length
> > using derived types and still have "*" return values of type Length,
> > when it should return an area.  He had a point, hadn't he?
> > OTOH, with only structural equivalence of types, and no way to derive
> > both an integral length type and an integral area type, that are really
> > diferent, how can you build areas into your types, such that the compiler
> > will prevent use of values of the wrong type?
> > 
> > In which languages has this been fixed?
> 
> This is relatively easy to do in C++.
> See http://www.fnal.gov/docs/working-groups/fpcltf/html/SIunits-summary.html

This is also easy in Ada.

For a collection of methods how to deal with dimensions in Ada, see
<http://home.T-Online.de/home/Christ-Usch.Grein/Ada/Dimension.html>

Re: Why is Ada NOT a good choice for a beginner to programming?

[Hyman Rosen]

Grein, Christoph wrote:
> This is also easy in Ada.

No, it is not. Of your referenced approaches, only Macks adopts
the spirit of the C++ solution, in which all unit operations are
checked at compile-time, and unit objects have no space overhead.
And Macks requires a seperate processing step to generate the
Ada code, and furthermore results in a combinatorial explosion
of declarations.

Re: Why is Ada NOT a good choice for a beginner to programming?

[Kevin Cline]

"Grein, Christoph" <christoph.grein@eurocopter.com> wrote in message news:<mailman.1042181162.27181.comp.lang.ada@ada.eu.org>...
> > > One complaint he had was that it be possible to define a Length
> > > using derived types and still have "*" return values of type Length,
> > > when it should return an area.  He had a point, hadn't he?
> > > OTOH, with only structural equivalence of types, and no way to derive
> > > both an integral length type and an integral area type, that are really
> > > diferent, how can you build areas into your types, such that the compiler
> > > will prevent use of values of the wrong type?
> > > 
> > > In which languages has this been fixed?
> > 
> > This is relatively easy to do in C++.
> > See http://www.fnal.gov/docs/working-groups/fpcltf/html/SIunits-summary.html
> 
> This is also easy in Ada.
> 
> For a collection of methods how to deal with dimensions in Ada, see
> <http://home.T-Online.de/home/Christ-Usch.Grein/Ada/Dimension.html>

Did you read Grein's paper?  He says that it was not easy at all.

Grein writes:

  But the request to have full dimensional checking persists as can be seen
  from the pertinent discussions in newsgroup Comp.Lang.Ada. There are two
  basic ways one can try to solve the problem, either by adding to the
  numeric value its dimension as attribute, or by using different types for
  different dimensions.  Since the first method is runtime-consuming,
  whereas the second one is only compiletime-consuming, all effort naturally
  concentrates on the second method.   This is doomed to fail
  as is shown in the paper cited above - although a plethora of overloaded
  operations is used, the result is not really satisfactory.
  Physical equations with all their powers and roots evade these attempts.

In short, Ada's requirement for explicit generic instantiation repels
attempts to create a compile-time verified system of dimensional types,
and Grein gave up on attempts to achieve compile-time type safety.

C++ does not have this problem, and compile-time type safety is
achieved in a fairly obvious way.

Re: Why is Ada NOT a good choice for a beginner to programming?

[Kevin Cline]

"Grein, Christoph" <christoph.grein@eurocopter.com> wrote in message news:<mailman.1042181162.27181.comp.lang.ada@ada.eu.org>...
> > > One complaint he had was that it be possible to define a Length
> > > using derived types and still have "*" return values of type Length,
> > > when it should return an area.  He had a point, hadn't he?
> > > OTOH, with only structural equivalence of types, and no way to derive
> > > both an integral length type and an integral area type, that are really
> > > diferent, how can you build areas into your types, such that the compiler
> > > will prevent use of values of the wrong type?
> > > 
> > > In which languages has this been fixed?
> > 
> > This is relatively easy to do in C++.
> > See http://www.fnal.gov/docs/working-groups/fpcltf/html/SIunits-summary.html
> 
> This is also easy in Ada.
> 
> For a collection of methods how to deal with dimensions in Ada, see
> <http://home.T-Online.de/home/Christ-Usch.Grein/Ada/Dimension.html>

Christopher,

I apologize for not noticing that you were referring to your own paper.
But in the paper you mention numerous shortcomings
of the implementation:

  "Ada is not suited to handling physical dimensions!"

and

  ...we can include semantic information within variable declarations...

  g: Meter_Per_Second_2 := 9.81;
  t: Second             := 10.0;
  s: Meter              := 0.5 * g * t**2;
  
  It is the programmer's own responsibility that this formula is physically 
  correct, no type checking is done! 

  ...There is one service restriction: 
    Checks in assignments concerning physical dimensions are not performed. 

The C++ solution affords full compile-time checking of assignments,
and will not allow a quantity of one dimensionality to be assigned
to a variable of another dimensionality except by resorting to
a reinterpret-cast.

Dimension checking was RE: Why is Ada NOT a good choice for a beginner to programming?

[Robert C. Leif]

An obvious fix, which was discussed at SIGAda 2002, is to develop a means
(Pragma?) to tell the compiler to only check the dimensionality at compile
time. This could be in the form of a compile time assertion.
Bob Leif

-----Original Message-----
From: comp.lang.ada-admin@ada.eu.org [mailto:comp.lang.ada-admin@ada.eu.org]
On Behalf Of Kevin Cline
Sent: Friday, January 10, 2003 7:51 AM
To: comp.lang.ada@ada.eu.org
Subject: Re: Why is Ada NOT a good choice for a beginner to programming?

"Grein, Christoph" <christoph.grein@eurocopter.com> wrote in message
news:<mailman.1042181162.27181.comp.lang.ada@ada.eu.org>...
> > > One complaint he had was that it be possible to define a Length
> > > using derived types and still have "*" return values of type Length,
> > > when it should return an area.  He had a point, hadn't he?
> > > OTOH, with only structural equivalence of types, and no way to derive
> > > both an integral length type and an integral area type, that are
really
> > > diferent, how can you build areas into your types, such that the
compiler
> > > will prevent use of values of the wrong type?
> > > 
> > > In which languages has this been fixed?
> > 
> > This is relatively easy to do in C++.
> > See
http://www.fnal.gov/docs/working-groups/fpcltf/html/SIunits-summary.html
> 
> This is also easy in Ada.
> 
> For a collection of methods how to deal with dimensions in Ada, see
> <http://home.T-Online.de/home/Christ-Usch.Grein/Ada/Dimension.html>

Did you read Grein's paper?  He says that it was not easy at all.

Grein writes:

  But the request to have full dimensional checking persists as can be seen
  from the pertinent discussions in newsgroup Comp.Lang.Ada. There are two
  basic ways one can try to solve the problem, either by adding to the
  numeric value its dimension as attribute, or by using different types for
  different dimensions.  Since the first method is runtime-consuming,
  whereas the second one is only compiletime-consuming, all effort naturally
  concentrates on the second method.   This is doomed to fail
  as is shown in the paper cited above - although a plethora of overloaded
  operations is used, the result is not really satisfactory.
  Physical equations with all their powers and roots evade these attempts.

In short, Ada's requirement for explicit generic instantiation repels
attempts to create a compile-time verified system of dimensional types,
and Grein gave up on attempts to achieve compile-time type safety.

C++ does not have this problem, and compile-time type safety is
achieved in a fairly obvious way.

Re: Dimension checking was RE: Why is Ada NOT a good choice for a beginner to programming?

[Stephen Leake]

"Robert C. Leif" <rleif@rleif.com> writes:

> An obvious fix, which was discussed at SIGAda 2002, is to develop a means
> (Pragma?) to tell the compiler to only check the dimensionality at compile
> time. This could be in the form of a compile time assertion.

Or an ASIS tool that reads structured comments to get the units.

-- 
-- Stephe

Re: Dimension checking was RE: Why is Ada NOT a good choice for a beginner to programming?

[Kevin Cline]

"Robert C. Leif" <rleif@rleif.com> wrote in message news:<mailman.1042310041.30777.comp.lang.ada@ada.eu.org>...
> An obvious fix, which was discussed at SIGAda 2002, is to develop a 
> means
> (Pragma?) to tell the compiler to only check the dimensionality at 
> compile
> time. This could be in the form of a compile time assertion.
> Bob Leif

I don't know what the proposal encompassed, but it's hard for me to imagine
an "obvious" fix to this problem.  With physical dimensions we have 
   Qty<L1,M1,T1,...> * Qty<L2,M2,T2,...> => Qty<L1+L2,M1+M2,T1+T2,...>

where L1,M1,T1,L2,M2,T2 are the dimensions of length, mass, time, etc.
However, there are many systems of physical units in use in different
problem domains.  For example, it is often convenient to make length
and time interchangable.

And in matrix algebra we have:
   innerProduct(Matrix<M,N>, Matrix<N,P>) => Matrix<M,P>

Any solution adopted should be able to correctly model 
both of these type systems.