Newbie question:procedural variables(call by reference)?

Newbie question:procedural variables(call by reference)?

[Dmytry Lavrov]

There are no procedural variables(calls by reference) in ADA,right?(or i
missed something...).
How to live without 'em? (i guess , 'like in java' ;-)

What for example if i have wrote,say.... expression evaluator.
In Pascal(bit extended),
and with way to add custom functions,like

procedure
AddFunc(name:string;numparams:integer;additionalparam:mashine_word;fn:CustomFunction);

How i can move it to ada....(of course i know that it's sometimes better
to do all with OOP,but here is much simpler to have array with
references ,than doing crazy extensible objects).
Normally i can use something like
type FunctionInfo=record

name:string;numparams:integer;additionalparam:mashine_word;fn:CustomFunction;
end;
and simple sorted array of 'em,finding right routine by binary search.



Why peoples sometime talking about OS in ada?...it's inpossible w/o call
by reference,OOP is based on call by reference,right?.

Heh,formally running a program from hard disk is a call by reference!
;-).

Re: Newbie question:procedural variables(call by reference)?

[Stephen Leake]

Dmytry Lavrov <m31415@mail.ru> writes:

> There are no procedural variables(calls by reference) in ADA,right?(or i
> missed something...).

You can pass a pointer to a subprogram as a parameter to an Ada
subprogram. Generally, the subprogram must be a library-level
subprogram, but sometimes you can use a local subprogram.

> How to live without 'em? (i guess , 'like in java' ;-)

Generics usually provide a better way to get the same result. "Better"
here means more type-safe, more easily understood.

-- 
-- Stephe

Re: Newbie question:procedural variables(call by reference)?

[Gautier Write-only]

Dmytry Lavrov:

> There are no procedural variables(calls by reference) in ADA,right?(or i
> missed something...).

I'm afraid you did ;-) : a small example (see the "My_feedback'access" etc.):
  http://www.mysunrise.ch/users/gdm/uza_html/unzipada__adb.htm#23_3

> How to live without 'em? (i guess , 'like in java' ;-)

You can also use the genericity (no bad jokes with pointers), see e.g.
"procedure Count_files..." there:
  http://www.mysunrise.ch/users/gdm/uza_html/comp_zip__adb.htm#108_13

Now you have to choose between TWO methods!
________________________________________________________
Gautier  --  http://www.mysunrise.ch/users/gdm/gsoft.htm

NB: For a direct answer, e-mail address on the Web site!

Re: Newbie question:procedural variables(call by reference)?

[Jeffrey Carter]

Dmytry Lavrov wrote:

> There are no procedural variables(calls by reference) in ADA,right?(or i
> missed something...).
> How to live without 'em? (i guess , 'like in java' ;-)
> 
> What for example if i have wrote,say.... expression evaluator.
> In Pascal(bit extended),
> and with way to add custom functions,like
> 
> procedure
> AddFunc(name:string;numparams:integer;additionalparam:mashine_word;fn:CustomFunction);

This is called access-to-subprogram in Ada; see ARM 3.10. You'd want 
something like

type Custom_Function is access function (...) return Whatever;

procedure Add_Func (Name              : in String;
                     Num_Params        : in Natural;
                     Additional_Params : in Machine_Word;
                     Func              : in Custom_Function);

Note, however, the restrictions on nesting.

-- 
Jeff Carter
"Mr. President, we must not allow a mine-shaft gap!"
Dr. Strangelove
33

Re: Newbie question:procedural variables(call by reference)?

[Georg Bauhaus]

Jeffrey Carter <spam@spam.com> wrote:

: "Mr. President, we must not allow a mine-shaft gap!"

(That is General Turgidson speaking, though, not Dr. Strangelove
:-) :-)

Re: Newbie question:procedural variables(call by reference)?

[Matthew Heaney]

Dmytry Lavrov <m31415@mail.ru> writes:

> There are no procedural variables(calls by reference) in Ada,right?
> (or I missed something...)

Yes, there are procedure variables in Ada95:

  type Procedure_Access is
     access procedure (I : Integer);

  type Function_Access is
     access function (I : Integer) return Float;

> How to live without 'em? (i guess , 'like in java' ;-)

You don't have to, but you have procedure pointers in Ada95.

However, you probably don't need them.  Instead, you'll probably want to
use a "generic formal subprogram," like this:

generic
  with procedure Process (I : Integer) is <>;
procedure Generic_Op;

To call Op, you must "instantiate" it, and supply the procedure a the
"generic actual argument," like this:

procedure Process (I : Integer) is ...;

procedure Op is new Generic_Op (Process);

Now you can call Op, and it will call Process.

 
> What for example if I have wrote, say.... expression evaluator.  In
> Pascal(bit extended), and with way to add custom functions, like
> 
> procedure AddFunc
>   (name:string;
>    numparams:integer;
>    additionalparam:machine_word;
>    fn:CustomFunction);

You could use a function pointer here, but you probably don't want to.
To convert this to Ada95, to this:

generic
   with procedure Custom_Function (O : T) is <>;
procedure Generic_AddFunc
  (Name : String;
   NumParams : Integer;
   AdditionalParam : Integer_32);

You first have to instantiate Generic_AddFunc, and supply an actual
Custom_Function.  Something like:

procedure Do_Something (O : T);

procedure AddFunc is new Generic_AddFunc (Do_Something);


> How I can move it to Ada....(of course I know that it's sometimes
> better to do all with OOP, but here is much simpler to have array with
> references, than doing crazy extensible objects).

See above.


> Why peoples sometime talking about OS in ada?...it's inpossible w/o call
> by reference,OOP is based on call by reference,right?.

Yes, OOP is done with call-by-reference.  Tagged types in Ada95 are
passed by reference, so dispatching works.

Re: Newbie question:procedural variables(call by reference)?

[Dmytry Lavrov]

Thanks,

i found that i misunderstand sentence
like "without procedural variables we can ........ at compile time"
(in context of "without pointer arifmetics ....")