RE: [sv-bc] Mantis 1571: proposal for macro defaults

You're correct, of course. I thought I had done those changes after
copy-pasting the line. 

I would like to add a sentence that the special combinations `", ``, and
`\ in actual arguments and in defaults are considered normal characters
and do not have the special meanings that they do in macro text.

Shalom

> -----Original Message-----
> From: Gordon Vreugdenhil [mailto:gordonv@model.com] 
> Sent: Monday, November 26, 2007 11:02 AM
> To: Bresticker, Shalom
> Cc: sv-bc
> Subject: Re: [sv-bc] Mantis 1571: proposal for macro defaults
> 
> Shalom,  I think there is an issue with the example:
> 
>     `define MACRO2(a=5, b, c="C") $display(a,,b,,c); ...
>     `MACRO2 (, 2, )     // a and c omitted, replaced by defaults
>                         // expands to '$display(1,,2,,"C");'
>                                                ^^^
> 
>     `MACRO2 (, 2)       // a and c omitted, replaced by defaults
>                         // expands to '$display(1,,2,,"C");'
>                                                ^^^
> 
> The ones in the $display expansions should be fives.
> 
> The rest appears fine.
> 
> Gord.
> 
> 
> 
> Bresticker, Shalom wrote:
> > Hi,
> > 
> > I have attached a revised version of this proposal that deals with 
> > most of the comments received. I left two issues out as 
> being outside 
> > the scope of this Mantis:
> > 
> > 1. Eric wrote:
> > 
> > '* Shalom's proposed change contains the following paragraph:
> > "If formal arguments are used, the list of formal argument 
> names shall 
> > be enclosed in parentheses following the name of the macro. 
> The formal 
> > argument names shall be simple_identifiers, separated by commas and 
> > optionally whitespace. The left parenthesis shall follow the text 
> > macro name immediately, with no space in between."
> > 
> > The LRM allows macros to be named with escaped identifiers. If an 
> > escaped identifier names the macro then one character of 
> white space 
> > (space, tab, newline, eof) must be used to delimit the 
> macro name as 
> > defined in section A.9.3 and A.9.4. First of all, does this 
> make sense?
> > Should language be added that indicates that one, and only 
> one space 
> > character or tab character separate the escaped identifier from the 
> > opening parenthesis?'
> > 
> > However, the text that Eric quotes is not mine, but is in 
> the existing 
> > LRM. It also has no connection to defaults.
> > 
> > 2. Greg wrote:
> > 
> >>    2) So-called "token gluing" (actually implemented as 
> >> token-delimiter
> >>       removal) has to be placed into this evaluation sequence
> >>       carefully.  The LRM describes '' only when it 
> appears in "macro 
> >> text",
> >>       and shows that it is removed sometime after the formal 
> >> substitutions
> >>       for the macro definition in which it appears.  It is 
> probably 
> >> already
> >>       true that gluing can produce tokens which will be subject to 
> >> further
> >>       macro expansion (but not to any further formal 
> substitution, of 
> >> course).
> >>       If it does act on the "literal" text, then it should 
> be able to
> >>       modify expansions latent in such text:
> >>
> >> 	`define CHAR_1  A
> >> 	`define CHAR_2  B
> >> 	`define CHAR_3  C
> >> 	`define CHAR_12 L
> >> 	`define BOT( X, Y, Z )  `" `CHAR_``X``Y``2`CHAR_``X `CHAR_``Z `"
> >>
> >>         `BOT( 1, `CHAR_1, 3 )   expands to  " ALA C "
> > 
> > I left this out as well as being connected to token gluing 
> and not to 
> > defaults.
> > 
> > I put the previous series of comments into the Mantis for easy 
> > reference.
> > 
> > The proposal incorporates changes from Mantis 1957, which 
> was already 
> > approved by SV-BC and practically, also by the Champions.
> > 
> > Please review the new proposal. We don't have much time left.
> > 
> > Thanks,
> > Shalom
> > 
> ---------------------------------------------------------------------
> > Intel Israel (74) Limited
> > 
> > This e-mail and any attachments may contain confidential 
> material for 
> > the sole use of the intended recipient(s). Any review or 
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> > by others is strictly prohibited. If you are not the intended 
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> > 
> > 
> > 
> > 
> ----------------------------------------------------------------------
> > --
> > 
> > Mantis 1571
> > 
> > P1800-2008/D3a
> > 
> > Add defaults for text macro arguments
> > 
> > The proposal is based on
> > 
> > In Section 21.5.1
> > 
> > CHANGE
> > 
> > Change the syntax in Syntax 21-2 from
> > 
> > list_of_formal_arguments ::=
> >     formal_argument_identifier { , formal_argument_identifier } 
> > formal_argument_identifier ::=
> >     simple_identifier
> > 
> > TO
> > 
> > list_of_formal_arguments ::=
> >     formal_argument_identifier { , formal_argument_identifier }
> >     formal_argument { , formal_argument } formal_argument ::=
> >     simple_identifier [ = default_text ] formal_argument_identifier 
> > ::=
> >     simple_identifier
> > 
> > 
> > CHANGE
> > 
> >  
> > 
> > If formal arguments are used, the list of formal argument 
> names shall 
> > be enclosed in parentheses following
> > 
> > the name of the macro. The formal argument names shall be 
> > /simple_identifiers/, separated by commas and
> > 
> > optionally whitespace. The left parenthesis shall follow the text 
> > macro name immediately, with no space in between.
> > 
> > 
> > TO
> > 
> >  
> > 
> > If formal arguments are used, the list of formal argument 
> names shall 
> > be enclosed in parentheses following
> > 
> > the name of the macro. The formal argument names shall be 
> > /simple_identifiers/, separated by commas and
> > 
> > optionally whitespace. The left parenthesis shall follow the text 
> > macro name immediately, with no space in between.
> > 
> > 
> > A formal macro argument may have a default. A default is 
> specified by 
> > appending an "=" symbol after the formal argument name, followed by 
> > the default text. The default text is substituted for the formal 
> > argument if no corresponding actual argument is specified.
> > 
> > The default text may be explicitly specified to be empty by 
> adding an 

> > "=" symbol after the formal argument name, followed by a 
> comma (or a 
> > right parenthesis if it is the last argument in the argument list.)
> > 
> >  
> > 
> >  
> > 
> > CHANGE
> > 
> >  
> > 
> > To use a macro defined with arguments, the name of the text macro 
> > shall be followed by a list of actual arguments in parentheses, 
> > separated by commas. White space shall be allowed between the text 
> > macro name and the left parenthesis.
> > 
> >  
> > 
> > The number of actual arguments shall match the number of formal 
> > arguments. However,  an actual argument may be empty or white space 
> > only, in which case the formal argument is substituted by nothing.
> > Commas must still be used to maintain the correct number of 
> arguments.
> > 
> >  
> > 
> > Example:
> > 
> > `define D(x,y) *initial* $display("start", x , y, "end");
> > 
> >  
> > 
> > `D( "msg1" , "msg2" ) // prints "startmsg1msg2end"
> > 
> > `D( " msg1", )        // prints "start msg1 end"
> > 
> > `D(, "msg2 ")         // prints "start msg2 end"
> > 
> > `D(,)                 // prints "start  end"
> > 
> > `D(  ,  )             // prints "start  end"
> > 
> > `D("msg1")            // illegal, only one argument
> > 
> > `D()                  // illegal, only one empty argument
> > 
> > * *
> > 
> > *(The green text was added by Mantis 1957.)*
> > 
> > TO
> > 
> > To use a macro defined with arguments, the name of the text macro 
> > shall be followed by a list of actual arguments in parentheses, 
> > separated by commas. Actual arguments and defaults shall 
> not contain 
> > comma or right parenthesis characters outside matched pairs of left 
> > and right parentheses (), square brackets [], braces {}, 
> double quotes 
> > "", or an escaped identifier.
> > 
> >  
> > 
> > White space shall be allowed between the text macro name 
> and the left 
> > parenthesis in the macro usage.
> > 
> > If fewer actual arguments are specified than the number of formal 
> > arguments and all the remaining formal arguments have 
> defaults, then 
> > the defaults are substituted for the additional formal 
> arguments. It 
> > shall be an error if any of the remaining formal arguments does not 
> > have a default specified. For a macro with arguments,  the 
> parentheses 
> > are always required in the macro call, even if all the 
> arguments have 
> > defaults. For macros without arguments, it shall be an error to add 
> > parentheses. It shall be an error to specify more actual arguments 
> > than the number of formal arguments.
> > 
> >  
> > 
> > Example without defaults:
> > 
> > `define D(x,y) *initial* $display("start", x , y, "end");
> > 
> >  
> > 
> > `D( "msg1" , "msg2" ) // expands to '*initial* 
> $display("start", "msg1" 
> > , "msg2", "end");' prints "startmsg1msg2end"
> > 
> > `D( " msg1", )        // expands to '*initial* 
> $display("start", " msg1" 
> > , , "end");' prints "start msg1 end"
> > 
> > `D(, "msg2 ")         // expands to '*initial* $display("start",  , 
> > "msg2 ", "end");' prints "start msg2 end"
> > 
> > `D(,)                 // expands to '*initial* 
> $display("start",  , , 
> > "end");' prints "start  end"
> > 
> > `D(  ,  )             // expands to '*initial* 
> $display("start",  , , 
> > "end");' prints "start  end"
> > 
> > `D("msg1")            // illegal, only one argument
> > 
> > `D()                  // illegal, only one empty argument
> > 
> > `D(,,)                // illegal, more actual than formal arguments
> > 
> > Example with defaults:
> > 
> > `define MACRO1(a=5,b="B",c) $display(a,,b,,c);
> > 
> > `MACRO1 ( , 2, 3 )  // argument a omitted, replaced by default
> >                     // expands to '$display(5,,2,,3);'
> > `MACRO1 ( 1 , , 3 ) // argument b omitted, replaced by default
> >                     // expands to '$display(1,,"B",,3);'
> > `MACRO1 ( , 2, )    // ILLEGAL: c omitted, no default
> > `MACRO1 ( 1 )       // ILLEGAL: b and c omitted, no default for c
> > 
> > `define MACRO2(a=5, b, c="C") $display(a,,b,,c);
> > 
> > `MACRO2 (1, , 3)    // ILLEGAL: b omitted, no default
> > `MACRO2 (, 2, )     // a and c omitted, replaced by defaults
> >                     // expands to '$display(1,,2,,"C");'
> > `MACRO2 (, 2)       // a and c omitted, replaced by defaults
> >                     // expands to '$display(1,,2,,"C");'
> > 
> > `define MACRO3(a=5, b=0, c="C") $display(a,,b,,c);
> > `MACRO3 ( 1 )       // b and c omitted, replaced by defaults
> >                     // expands to '$display(1,,0,,"C");'
> > `MACRO3 ( )         // all arguments replaced by defaults
> >                     // expands to '$display(5,,0,,"C");'
> > `MACRO3             // ILLEGAL: parentheses required
> > 
> > CHANGE
> > 
> > Each actual argument is substituted for the corresponding formal 
> > argument literally. Therefore, when an expression is used 
> as an actual 
> > argument, the expression will be substituted in its 
> entirety. This may 
> > cause an expression to be evaluated more than once if the formal 
> > argument was used more than once in the macro text. For example:
> > 
> >  
> > 
> > `define max(a,b)((a) > (b) ? (a) : (b))
> > 
> > n = `max(p+q, r+s) ;
> > 
> > will expand as
> > 
> >  
> > 
> > n = ((p+q) > (r+s)) ? (p+q) : (r+s) ;
> > 
> > Here, the larger of the two expressions p + q and r + s will be 
> > evaluated twice.
> > 
> > TO
> > 
> > Each actual argument is substituted for the corresponding formal 
> > argument literally. Therefore, when an expression is used 
> as an actual 
> > argument, the expression will be substituted in its 
> entirety. This may 
> > cause an expression to be evaluated more than once if the formal 
> > argument was used more than once in the macro text. For example:
> > 
> >  
> > 
> > `define max(a,b)((a) > (b) ? (a) : (b))
> > 
> > n = `max(p+q, r+s) ;
> > 
> > will expand as
> > 
> >  
> > 
> > n = ((p+q) > (r+s)) ? (p+q) : (r+s) ;
> > 
> > Here, the larger of the two expressions p + q and r + s will be 
> > evaluated twice.
> > 
> >  
> > 
> > The macro text and argument defaults may contain usages of 
> other text 
> > macros. Such usages shall be substituted after the outer macro is 
> > substituted, not when it is defined. If an actual argument or an 
> > argument default contains a macro usage, the macro usage shall be 
> > expanded only after substitution into the outer macro text.
> > 
> >  
> > 
> > Note that if a formal argument has a non-empty default and 
> one wants 
> > to replace the formal argument with an empty actual argument, one 
> > cannot simply omit the actual argument, as then the default 
> will be used.
> > However, one can define an empty text macro, say `EMPTY, 
> and use that 
> > as the actual argument. This will be substituted in place of the 
> > formal argument, and will be replaced after expansion by empty text.
> > 
> >  
> > 
> > When a macro usage is passed as an actual argument to 
> another macro, 
> > the argument expansion shall not introduce new uses of the formal 
> > arguments to the top-level macro.
> > 
> >   `define TOP(a,b) a + b
> >   `TOP( `TOP(b,1), `TOP(42,a) )
> > 
> > expands to: b + 1 + 42 + a
> > not into: 42 + a + 1 + 42 + a
> > nor into: b + 1 + 42 + b + 1
> > 
> > It shall be an error for a macro to expand directly or 
> indirectly to 
> > text containing another usage of itself (a recursive macro).
> > 
> 
> --
> --------------------------------------------------------------------
> Gordon Vreugdenhil                                503-685-0808
> Model Technology (Mentor Graphics)                gordonv@model.com
> 
---------------------------------------------------------------------
Intel Israel (74) Limited

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