Newbie question (Range Specifiers)

Newbie question (Range Specifiers)

[Sandeep V. Kharkar]

Hi,

	I've recently started studying the Ada95 language.
	First experience with Ada...

	In the book I found a grammer rule for range specifiers
	which goes

	range_spec ::= name ' range ( static_expression )

	but I found no examples of the use of this grammer rule.
	
	What is this syntax used for ??

	I figure that the [name'range] means the range
	of the variable name. But what interpretation does the
	braketed static expression have on the range ??
-- 
~Sandeep

skharkar@vzcorp.com
http://www.cs.usu.edu/students/SandeepKharkar/index.html

"To know recursion you must first know recursion !!"

Re: Newbie question (Range Specifiers)

[Kevin J. Weise]

"Sandeep V. Kharkar" <skharkar@vzcorp.com> wrote:
>Hi,
>
>	I've recently started studying the Ada95 language.
>	First experience with Ada...
>
>	In the book I found a grammer rule for range specifiers
>	which goes
>
>	range_spec ::= name ' range ( static_expression )
>
>	but I found no examples of the use of this grammer rule.
>	
>	What is this syntax used for ??
>
>	I figure that the [name'range] means the range
>	of the variable name. But what interpretation does the
>	braketed static expression have on the range ??
>-- 

I've been in this business long enough that the region in my brain previously 
occupied by the Ada83 LRM has been recovered and filled with application-specific 
trivia; there isn't enough room left to memorize the Ada95 LRM.  But in a brief scan 
of the Ada95 RM (principally in Annex P, the Syntax Summary and the Syntax Cross 
Reference), I couldn't find the nonterminals or the production you specified above. 
 Can you please come back with a specific reference (i.e., document, section, page 
number, whatever) where you found this beastie?  I'd love to dig into it & find the 
answer myself.

----------------------------------------------------------------------------------

Kevin J. Weise          kweise@c3i-ccmail.sed.redstone.army.mil
COLSA Corporation       voice:  (205) 842-9680
Huntsville, AL

Serving the U.S. Army Missile Command, Software Engineering Directorate
standard disclaimers apply...

Re: Newbie question (Range Specifiers)

[Sandeep V. Kharkar]

Sandeep V. Kharkar (I Myself) wrote:
>	  RE :: grammer rule --> 
>         range_spec ::= name ' range ( static_expression )
>         but I found no examples of the use of this grammer rule.
>         What is this syntax used for ??

	In response I got two mail replies...
	For the sake of completeness here's 
	a summary of the replies...

	This is related to multidimensional arrays.
	The argument between brackets specifies which 
	dimension is concerned.

	EXAMPLE ::
		A : array (1..2, 1..5) of integer;
		A'range(2) = 1..5

	Similarly the attributes 'FIRST, 'LAST and 
	'LENGTH also have subscripted versions
	for use with multi-dimensional arrays.

	My ThanX to Mark Biggar and Laurent Gasser.
	
-- 
~Sandeep

skharkar@vzcorp.com
http://www.cs.usu.edu/students/SandeepKharkar/index.html

"To know recursion you must first know recursion !!"

Re: Newbie question (Range Specifiers)

[Keith Thompson]

In <4qbvma$ajd@michp1.redstone.army.mil> "Kevin J. Weise" <kweise@c3i-ccmail.sed.redstone.army.mil> writes:
> "Sandeep V. Kharkar" <skharkar@vzcorp.com> wrote:
[...]
> >	In the book I found a grammer rule for range specifiers
> >	which goes
> >
> >	range_spec ::= name ' range ( static_expression )
> >
> >	but I found no examples of the use of this grammer rule.
> >	
> >	What is this syntax used for ??
[...]
> I've been in this business long enough that the region in my brain
> previously occupied by the Ada83 LRM has been recovered and filled with
> application-specific trivia; there isn't enough room left to memorize
> the Ada95 LRM.  But in a brief scan of the Ada95 RM (principally in
> Annex P, the Syntax Summary and the Syntax Cross Reference), I couldn't
> find the nonterminals or the production you specified above.  Can you
> please come back with a specific reference (i.e., document, section,
> page number, whatever) where you found this beastie?  I'd love to dig
> into it & find the answer myself.

It's in section 4.1.4 of Annex P:

    4.1.4:
    range_attribute_reference ::= prefix'range_attribute_designator
 
    4.1.4:
    range_attribute_designator ::= Range[(static_expression)]

The static_expression, if present, specifies which dimension of an array
the range attribute refers to.  For example, given the declarations
 
    type Matrix is array(Positive range <>, Positive range <>) of Float;
    M: Matrix(1 .. 10, 1 .. 20);

M'Range(1) is 1 .. 10, and M'Range(2) is 1 .. 20.  The same applies to
the 'First, 'Last, and 'Length attributes.

See also the definition of the 'Range attribute in Annex K.

This was defined slightly differently in Ada 83, but with essentially
the same effect.

-- 
Keith Thompson (The_Other_Keith) kst@thomsoft.com <*>
TeleSoft^H^H^H^H^H^H^H^H Alsys^H^H^H^H^H Thomson Software Products
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