Basics : many way to use a Procedure

Basics : many way to use a Procedure

[comicfanzine]

Hello !

I'm seeing that some people use procedure with the sign " => " .
What is it ? Any documentation about this ? 

A example =

Ada.Text_IO.Create (
          File => Log_File,
          Name => "my_log_file.txt",
          Mode => Ada.Text_IO.Out_File);


which is very similar to the prototype :

 procedure Open
     (File : in out File_Type;
      Mode : File_Mode;
      Name : String;
      Form : String := "");

Also , is it possible to apply this kind of writing  for this procedure ? =

procedure Gtk_New
     (Window   : out Gtk_Window;
      The_Type : Gtk.Enums.Gtk_Window_Type := Gtk.Enums.Window_Toplevel);


Thanks for your answers :)

Re: Basics : many way to use a Procedure

[Jeffrey R. Carter]

On 12/11/2015 03:19 PM, comicfanzine@gmail.com wrote:
> 
> Ada.Text_IO.Create (
>           File => Log_File,
>           Name => "my_log_file.txt",
>           Mode => Ada.Text_IO.Out_File);
> 
> which is very similar to the prototype :
> 
>  procedure Open
>      (File : in out File_Type;
>       Mode : File_Mode;
>       Name : String;
>       Form : String := "");

This is a procedure declaration. Ada doesn't have prototypes. Also, this is the
declaration for Open, not Create.

This is an example of named parameter associations, often called named notation
for short; the other way is positional notation. They have the form

Formal_Parameter => Actual_Parameter

See ARM 6.4:

http://www.adaic.org/resources/add_content/standards/12rm/html/RM-6-4.html

Named notation is often used for procedure calls. They can make the call easier
to understand, and allow the order of the parameters to differ from those in the
declaration, as in your example.

For function calls, it's usually clearer to use positional notation for the 1st
parameter, IMO:

Image (Some_Value);

rather than

Image (Item => Some_Value);

> Also , is it possible to apply this kind of writing  for this procedure ? =
> 
> procedure Gtk_New
>      (Window   : out Gtk_Window;
>       The_Type : Gtk.Enums.Gtk_Window_Type := Gtk.Enums.Window_Toplevel);

Of course:

Gtk.Something.Gtk_New
   (Window => Msg_Window[, The_Type => Gtk.Enums.Some_Value]);

-- 
Jeff Carter
"I like it when the support group complains that they have
insufficient data on mean time to repair bugs in Ada software."
Robert I. Eachus
91

Re: Basics : many way to use a Procedure

[comicfanzine]

Edit : Sorry for the mistake .

I'm trying to understand the A.R.M .
When programming , it's difficult to apply it .

No , in fact , i'm lost... :

actual_parameter_part ::= 
    (parameter_association {, parameter_association})

parameter_association ::= 
   [formal_parameter_selector_name =>] explicit_actual_parameter

explicit_actual_parameter ::= expression | variable_name

------- Each time i code , i'm getting a long list of errors .

I tried to apply the A.R.M with this , without success :

procedure Gtk_New
      (Window   : out Gtk_Window;
       The_Type : Gtk.Enums.Gtk_Window_Type := Gtk.Enums.Window_Toplevel);

And i still don't find a tutorial or code example who explain simply those strange writin forms :(

Re: Basics : many way to use a Procedure

[Niklas Holsti]

On 15-12-12 05:25 , comicfanzine@gmail.com wrote:
> ------- Each time i code , i'm getting a long list of errors .

Show your code and the error messages, perhaps we can give better help then.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .

Re: Basics : many way to use a Procedure

[Lucretia]

On Friday, 11 December 2015 22:19:55 UTC, comicf...@gmail.com  wrote:
> Hello !
> 
> I'm seeing that some people use procedure with the sign " => " .
> What is it ? Any documentation about this ? 
> 
> A example =
> 
> Ada.Text_IO.Create (
>           File => Log_File,
>           Name => "my_log_file.txt",
>           Mode => Ada.Text_IO.Out_File);

It's called named parameter association. It allows you to change the order of the parameters passed to a function/procedure to one that makes reading easier or just your own preference.

> which is very similar to the prototype :
> 
>  procedure Open
>      (File : in out File_Type;
>       Mode : File_Mode;
>       Name : String;
>       Form : String := "");

For example, given the proper context clauses:

Open (Name => "hello.txt", File => My_File, Mode => In_File);

or you can use it partially, as in:

Open (My_File, Name => "hello.txt", Mode => In_File);

> Also , is it possible to apply this kind of writing  for this procedure ? =

You can apply it to all functions/procedures. 

Luke.

Re: Basics : many way to use a Procedure

[mockturtle]

On Saturday, December 12, 2015 at 4:25:27 AM UTC+1, comicf...@gmail.com wrote:
> Edit : Sorry for the mistake .
> 
> I'm trying to understand the A.R.M .
> When programming , it's difficult to apply it .
> 
> No , in fact , i'm lost... :

Welcome to the club :-) (although I am not a member of it anymore).

The ARM is written in "computer science legalese," one of the most obscure form of communication after cryptography... :-)  

Seriously, the ARM is not a tutorial, but a standard document and this kind of prose is a consequence of that.  I know that the ARM is not an easy reading when you are a beginner, but you'll get used to it and then it will be a fundamental and precious reference for you (personal experience).

What the excerpt that you posted say is that an actual_parameter_part is a sequence of one or more parameter_association separated by comma and included between parenthesis.  Every parameter_association can be both a value (called explicit_actual_parameter in the grammara) or a string of type "name => value" (where name is an identifier and its called formal_parameter_association_name in the grammar).

If you post your code and the error message, we can be more precise.

Riccardo

Re: Basics : many way to use a Procedure

[comicfanzine]

Thanks for your answers everybody :)

But , i still don't know where this sign come from : " => " . Any information or A.R.M documentation about it ??

Also , how to use this ?? =

actual_parameter_part ::= 
    (parameter_association {, parameter_association})

And this ?? =

parameter_association ::= 
   [formal_parameter_selector_name =>] explicit_actual_parameter


For the moment , i figured out how to use this ( at least :) ) =

procedure_call_statement ::= 
    procedure_name;
  | procedure_prefix actual_parameter_part;

I used it like this :

    WITH Gtk.Main ;          USE Gtk.Main ;
    WITH Gtk.Window ;        USE Gtk.Window ;
    WITH Gtk.Enums ;         USE Gtk.Enums ;

    Procedure procedure_gtkada is
    
        win : Gtk_window ;
     
    begin
    
     Init ; 
     
	Gtk_New(Window => Win, 
		The_Type => Gtk.Enums.Window_Toplevel); 
			       
-- procedure Gtk_New
   --  (Window   : out Gtk_Window;
   --   The_Type : Gtk.Enums.Gtk_Window_Type := Gtk.Enums.Window_Toplevel);
     
     Show_all(win) ; 
     
       Main ; 
	
end procedure_gtkada;

-- Compile with : gnatmake procedure_gtkada `gtkada-config`
-- Of course you need the libgtkada .

Re: Basics : many way to use a Procedure

[Jeffrey R. Carter]

On 12/12/2015 07:41 AM, comicfanzine@gmail.com wrote:
> 
> But , i still don't know where this sign come from : " => " . Any information or A.R.M documentation about it ??

This is a compound delimiter, known in Ada as an arrow (ARM 2.2). It's used to
associate something on the left with the thing on the right, as in
subprogram-call parameter lists, generic instantiations, and aggregates.

> 	Gtk_New(Window => Win, 
> 		The_Type => Gtk.Enums.Window_Toplevel); 

It appears that you understand this.

-- 
Jeff Carter
"English bed-wetting types."
Monty Python & the Holy Grail
15

Re: Basics : many way to use a Procedure

[Simon Wright]

comicfanzine@gmail.com writes:

> But , i still don't know where this sign come from : " => " . Any
> information or A.R.M documentation about it ??
>
> Also , how to use this ?? =
>
> actual_parameter_part ::= 
>     (parameter_association {, parameter_association})
>
> And this ?? =
>
> parameter_association ::= 
>    [formal_parameter_selector_name =>] explicit_actual_parameter

ARM 6.4(13)?

http://www.ada-auth.org/standards/12rm/html/RM-6-4.html#p13

Re: Basics : many way to use a Procedure

[comicfanzine]

Le samedi 12 décembre 2015 19:28:03 UTC, Simon Wright a écrit :
> comicfanzine@gmail.com writes:
> 
> > But , i still don't know where this sign come from : " => " . Any
> > information or A.R.M documentation about it ??
> >
> > Also , how to use this ?? =
> >
> > actual_parameter_part ::= 
> >     (parameter_association {, parameter_association})
> >
> > And this ?? =
> >
> > parameter_association ::= 
> >    [formal_parameter_selector_name =>] explicit_actual_parameter
> 
> ARM 6.4(13)?
> 
> http://www.ada-auth.org/standards/12rm/html/RM-6-4.html#p13

The Examples form does not match this one =

actual_parameter_part ::= 
    (parameter_association {, parameter_association})

parameter_association ::= 
   [formal_parameter_selector_name =>] explicit_actual_parameter

explicit_actual_parameter ::= expression | variable_name

Re: Basics : many way to use a Procedure

[comicfanzine]

>> ARM 6.4(13)?
> 
> http://www.ada-auth.org/standards/12rm/html/RM-6-4.html#p13

The form is different =

actual_parameter_part ::= 
    (parameter_association {, parameter_association})

parameter_association ::= 
   [formal_parameter_selector_name =>] explicit_actual_parameter

explicit_actual_parameter ::= expression | variable_name

Still, i don't know how to use those forms .


Also i don't find in the A.R.M , a description of the possibillities for using = 

compound delimiters " => "

Re: Basics : many way to use a Procedure

[Simon Wright]

comicfanzine@gmail.com writes:

>>> ARM 6.4(13)?
>> 
>> http://www.ada-auth.org/standards/12rm/html/RM-6-4.html#p13
>
> The form is different =
>
> actual_parameter_part ::= 
>     (parameter_association {, parameter_association})
>
> parameter_association ::= 
>    [formal_parameter_selector_name =>] explicit_actual_parameter
>
> explicit_actual_parameter ::= expression | variable_name
>
> Still, i don't know how to use those forms .

In what way does the 4th example,

  Print_Header(128, Header => Title, Center => True);

not match those forms?

Perhaps you'd better post an example of what you think the ARM's syntax
is telling you to write.

Re: Basics : many way to use a Procedure

[comicfanzine]

> In what way does the 4th example,
> 
>   Print_Header(128, Header => Title, Center => True);
> 
> not match those forms?
> 
> Perhaps you'd better post an example of what you think the ARM's syntax
> is telling you to write.

the 4th example look a little like =

    [formal_parameter_selector_name =>] explicit_actual_parameter

but, there is no "[]" in the 4th example .

Also the 4th example doesn't look like this other form , there is no "{}" =

 actual_parameter_part ::= 
    (parameter_association {, parameter_association})

Re: Basics : many way to use a Procedure

[comicfanzine]

> > In what way does the 4th example,
> > 
> >   Print_Header(128, Header => Title, Center => True);
> > 
> > not match those forms?
> > 
> > Perhaps you'd better post an example of what you think the ARM's syntax
> > is telling you to write.
 
 the 4th example look a little like =
 
     [formal_parameter_selector_name =>] explicit_actual_parameter
 
 but, there is no "[]" in the 4th example .
 
 Also the 4th example doesn't look like this other form , there is no "{}" =
 
  actual_parameter_part ::= 
     (parameter_association {, parameter_association})

Also , what this next form means ? What means the delimiter " | " ?

explicit_actual_parameter ::= expression | variable_name

At the end , i don't find in the A.R.M , a description of the possibillities for using = compound delimiters " => " 

Re: Basics : many way to use a Procedure

[Jeffrey R. Carter]

On 12/12/2015 03:15 PM, comicfanzine@gmail.com wrote:
>>> In what way does the 4th example,
>>>
>>>   Print_Header(128, Header => Title, Center => True);
>>>
>>> not match those forms?
>>>
>>> Perhaps you'd better post an example of what you think the ARM's syntax
>>> is telling you to write.
>  
>  the 4th example look a little like =
>  
>      [formal_parameter_selector_name =>] explicit_actual_parameter
>  
>  but, there is no "[]" in the 4th example .
>  
>  Also the 4th example doesn't look like this other form , there is no "{}" =
>  
>   actual_parameter_part ::= 
>      (parameter_association {, parameter_association})
> 
> Also , what this next form means ? What means the delimiter " | " ?
> 
> explicit_actual_parameter ::= expression | variable_name

The BNF used to define the syntax is given in ARM 1.1.4.

http://www.adaic.org/resources/add_content/standards/12rm/html/RM-1-1-4.html

You need to be familiar with the notation before you read the rest of the ARM.

Brackets [] surround optional items; braces {} surround items that may appear
zero or more times; the vertical bar | separates alternatives. So

[formal_parameter_selector_name =>] explicit_actual_parameter

means "formal_parameter_selector_name =>" is optional; the parameter 128 in the
example has that part omitted.

actual_parameter_part ::=
   (parameter_association {, parameter_association})

means there's at least 1 parameter_association in an actual_parameter_part, and
if there are more than 1, the others are all preceded by a comma,

explicit_actual_parameter ::= expression | variable_name

means an explicit_actual_parameter is either an expression or a variable_name.

-- 
Jeff Carter
"English bed-wetting types."
Monty Python & the Holy Grail
15

Re: Basics : many way to use a Procedure

[comicfanzine]

@Jeff Carter= Thanks , i understand all now .

Re: Basics : many way to use a Procedure

[comicfanzine]

@Jeff Carter= Thanks , i understand all now . 

Also , i finally found clear examples for using " => "

https://en.wikibooks.org/wiki/Ada_Programming/Delimiters/arrow#Ada_Reference_Manual

Re: Basics : many way to use a Procedure

[comicfanzine]

@Jeff Carter= Thanks , i understand all now .

Also , i finally found clear examples for using " => " 

https://en.wikibooks.org/wiki/Ada_Programming/Delimiters/arrow#Contexts

Re: Basics : many way to use a Procedure

[Mark Lorenzen]

On Saturday, December 12, 2015 at 4:25:27 AM UTC+1, comicf...@gmail.com wrote:
> Edit : Sorry for the mistake .
> 
> I'm trying to understand the A.R.M .
> When programming , it's difficult to apply it .
> 
> No , in fact , i'm lost... :

I recommend that you use a textbook instead of the ARM.

Regards,

Mark L