Re: [$ieee-1850] IEEE 1850 PSL LRM draft 5....

Sounds good to me!

Best regards,

-Harry
---
Harry D. Foster
Chief Methodologist           
Jasper Design Automation
http://www.jasper-da.com
Tel: +1 650.966.0239     Cell: +1 650.804.5000
	

On Mar 17, 2005, at 11:51 AM, Erich Marschner wrote:

> Harry,
>
> The nonterminal Identifier is a special case in all languages, PSL 
> included.  An 'Identifier' is a lexical item that has a specific 
> lexical structure in each language.  Lexical structure (sequence of 
> characters) and syntactic structure (sequence of tokens) are 
> different, because syntactic tokens are separated by white space, 
> whereas characters in a lexical element are not.  Although some 
> languages attempt to use pseudo-syntactic productions to represent 
> lexical structure of Identifiers and other lexical elements, this 
> practice stretches the meaning of the notation used for syntactic 
> productions to the breaking point.  In fact, in many languages, the 
> lexical structure of 'Identifier' is not given in a pseudo-syntax 
> production, but rather in some other form (e.g., an English 
> description).
>
> In PSL, section 4.2.1 defines what PSL Identifiers consist of:
>
>     Identifiers in PSL consist of an alphabetic character, followed by 
> zero or more
>     alphanumeric characters; each subsequent alphanumeric character 
> may optionally be
>     preceded by a single underscore character.
>
> In Verilog 2001, Identifiers are similarly described in English:
>
>     2.7 Identifiers, keywods, and system names
>
>     An identifier is used to give an object a unique name so it can be 
> referenced.
>     An identifier is either a simple identifier or an escaped 
> identifier (see 2.7.1).
>     A simple identifier shall be any sequence of letters, digits, 
> dollar signs ($),
>     and underscore characters (_).
>
> The Verilog 2001 LRM does define identifer in the syntax summary, as
>
>     identifier ::=
>       simple_identifier
>     | escaped_identifer
>
> but apparently this production is not in the body of the LRM; only the 
> description in 2.7 appears.  The body of the LRM does contain a 
> pseudo-syntax production for simple_identifier:
>
>     simple_identifier ::= [ a-zA-Z_ ] { [ a-zA_Z0-9_$ ] }
>
> but note that this definition uses a different interpretation for 
> square braces than in other productions - here they mean "any 
> character in this set" rather than "optionally".  This is an 
> illustration of how the notation used for syntax productions is often 
> contorted when it is applied to defining lexical structure.
>
> In VHDL, the LRM does something similar, but ultimately gives up 
> trying to use syntax productions at the point where it needs to refer 
> to allowable characters.
>
> In short, I think the PSL LRM defines PSL Identifiers sufficiently in 
> 4.2.1, and that we should avoid the complications involved in trying 
> to represent the lexical structure of an Identifier with syntactic 
> productions.
>
> Note, by the way, that all references to PSL_Identifier should have 
> the PSL prefix italicized.  The same applies to all references to 
> VHDL_Identifier, Verilog_Identifier, etc.
>
> Regards,
>
> Erich
>
> | -----Original Message-----
> | From: owner-ieee-1850@eda.org
> | [mailto:owner-ieee-1850@eda.org] On Behalf Of Harry D. Foster
> | Sent: Thursday, March 17, 2005 12:00 PM
> | To: Cindy Eisner
> | Cc: ieee-1850@eda.org
> | Subject: Re: [$ieee-1850] IEEE 1850 PSL LRM draft 5....
> |
> | >
> | > harry,
> | >
> | >> Also, I would appreciate a good review of Annex A, the BNF.  I'm
> | >> worried about its accuracy.
> | >
> | > the definition of PSL_Identifier seems to be missing.  (i
> | can't take
> | > credit for being so observant:  i happened to be going over
> | some old
> | > emails and found such a comment from klaus from quite some
> | time ago -
> | > it seems that it still has not been addressed.)
> | >
> | > cindy.
> | >
> |
> | Yes--very good.   This problem is not limited to Annex A, but occurs
> | all over the
> | informal semantics, wherever PSL_Identifier occurs.
> |
> | Can someone give me a proposal I can edit in throughout the text?
> |
> | Thanks
> |
> | -Harry
> |
> |
> |
>