An ISO Standard Question

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5 total messages Started by gstark Tue, 27 Feb 1996 13:56

#3313

Author: gstark
Date: Tue, 27 Feb 1996 13:56

34 lines
1173 bytes

Dear All,

I wonder if someone out there could clarify something
in the ISO standard. 

Using one of the two "ISO Compliant" compilers we've tested (XDS), this is legal:

TYPE 
  Str = ARRAY[1 .. 10] OF CHAR;
  StrArr = ARRAY[1 .. 2] OF Str;
VAR 
  s : StrArr;
BEGIN
  s := StrArr{"Hello" , "Mum" };

... but this is *illegal*:

TYPE 
  Str = ARRAY[1 .. 10] OF CHAR;
  StrArr = ARRAY[1 .. 2] OF Str;
CONST 
  s = StrArr{"Hello" , "Mum"};

However this structured constant *is* allowed under GPM2, the other
"ISO-conformant" M2 compiler that we've been using. Which is right?
In our existing code (using TopSpeed) we declare a lot of arrays of
strings as constants. So we'd like GPM to be right!

And if it is the case that variable constructors are legal but constant
constructors illegal, what was the thinking behind it?

regards,

Graham Stark

Re: An ISO Standard Question

#3314

Author: Graham Perkins
Date: Tue, 27 Feb 1996 19:11

29 lines
1590 bytes

gstark@ifs.org.uk wrote:
>.. one of two "ISO Compliant" compilers we've tested (XDS), this is legal:
> VAR
>   s : StrArr;
> BEGIN
>   s := StrArr{"Hello" , "Mum" };
> 
> ... but this is *illegal*:
> 
> TYPE
>   Str = ARRAY[1 .. 10] OF CHAR;
>   StrArr = ARRAY[1 .. 2] OF Str;
> CONST
>   s = StrArr{"Hello" , "Mum"};
> 
> However this structured constant *is* allowed under GPM2,

I've got Fourth Draft of the ISO standard, which I believe was quite close to
the final.  It clearly states that the value given for a named constant in a 
constant declaration must be a constant expression.  It is also states that an
array constructor is a constant expression if its contents are constant expressions.
My understanding of that is that one could construct arbitrarily nested array/record
structures, so long as "leaf" items were constant values.

-- 
person: Graham Perkins         paper: School of Computing
voice:  +44 (0)1908 834936            De Montfort University
dots:   +44 (0)1908 834948            Milton Keynes MK7 6HP
bits:   grp@dmu.ac.uk                 United Kingdom

Re: An ISO Standard Question

#3323

Author: Alex Nedorya
Date: Wed, 28 Feb 1996 20:51

42 lines
1680 bytes

gstark@ifs.org.uk wrote:
> 
> Dear All,
> 
> I wonder if someone out there could clarify something
> in the ISO standard.
> 
> Using one of the two "ISO Compliant" compilers we've tested (XDS), this is legal:
> 
> TYPE
>   Str = ARRAY[1 .. 10] OF CHAR;
>   StrArr = ARRAY[1 .. 2] OF Str;
> VAR
>   s : StrArr;
> BEGIN
>   s := StrArr{"Hello" , "Mum" };
> 
> ... but this is *illegal*:
> 
> TYPE
>   Str = ARRAY[1 .. 10] OF CHAR;
>   StrArr = ARRAY[1 .. 2] OF Str;
> CONST
>   s = StrArr{"Hello" , "Mum"};

The XDS translator reports "Can not generate object declaration" error in the second case.
It does not have any connection with ISO standard. It is just a restriction in the code 
generator which generates C code. Both texts are valid accorording to the standard.

BTW, Native XDS (which generates native code for Win95/WinNT)
compiles both texts without problems. 

I cannot say now why this structure constant is not generated by our translator, 
I'll have a look.

BTW, new XDS web pages are available as
	http://www.iis.nsk.su/xtech/xds/
and will be available soon as
	http://www.dct.com/~johnm/xds.html

-- Alex Nedorya, xTech Ltd

Re: An ISO Standard Question

#3324

Author: Alex Nedorya
Date: Wed, 28 Feb 1996 20:52

46 lines
1688 bytes

gstark@ifs.org.uk wrote:
> 
> Dear All,
> 
> I wonder if someone out there could clarify something
> in the ISO standard.
> 
> Using one of the two "ISO Compliant" compilers we've tested (XDS), this is legal:
> 
> TYPE
>   Str = ARRAY[1 .. 10] OF CHAR;
>   StrArr = ARRAY[1 .. 2] OF Str;
> VAR
>   s : StrArr;
> BEGIN
>   s := StrArr{"Hello" , "Mum" };
> 
> ... but this is *illegal*:
> 
> TYPE
>   Str = ARRAY[1 .. 10] OF CHAR;
>   StrArr = ARRAY[1 .. 2] OF Str;
> CONST
>   s = StrArr{"Hello" , "Mum"};

The XDS translator reports "Can not generate object declaration" error 
in the second case.
It does not have any connection with ISO standard. It is just a 
restriction in the code 
generator which generates C code. Both texts are valid accorording to 
the standard.

BTW, Native XDS (which generates native code for Win95/WinNT)
compiles both texts without problems. 

I cannot say now why this structure constant is not generated by our 
translator, 
I'll have a look.

BTW, new XDS web pages are available as
	http://www.iis.nsk.su/xtech/xds/
and will be available soon as
	http://www.dct.com/~johnm/xds.html

-- Alex Nedorya, xTech Ltd

Re: An ISO Standard Question

#3325

Author: Alex Nedorya
Date: Wed, 28 Feb 1996 20:53

46 lines
1688 bytes

gstark@ifs.org.uk wrote:
> 
> Dear All,
> 
> I wonder if someone out there could clarify something
> in the ISO standard.
> 
> Using one of the two "ISO Compliant" compilers we've tested (XDS), this is legal:
> 
> TYPE
>   Str = ARRAY[1 .. 10] OF CHAR;
>   StrArr = ARRAY[1 .. 2] OF Str;
> VAR
>   s : StrArr;
> BEGIN
>   s := StrArr{"Hello" , "Mum" };
> 
> ... but this is *illegal*:
> 
> TYPE
>   Str = ARRAY[1 .. 10] OF CHAR;
>   StrArr = ARRAY[1 .. 2] OF Str;
> CONST
>   s = StrArr{"Hello" , "Mum"};

The XDS translator reports "Can not generate object declaration" error 
in the second case.
It does not have any connection with ISO standard. It is just a 
restriction in the code 
generator which generates C code. Both texts are valid accorording to 
the standard.

BTW, Native XDS (which generates native code for Win95/WinNT)
compiles both texts without problems. 

I cannot say now why this structure constant is not generated by our 
translator, 
I'll have a look.

BTW, new XDS web pages are available as
	http://www.iis.nsk.su/xtech/xds/
and will be available soon as
	http://www.dct.com/~johnm/xds.html

-- Alex Nedorya, xTech Ltd

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