Re: [PATCH 6/6] doc: api.value.type union.

[Akim Demaille]

Le 23 févr. 2013 à 17:00, Akim Demaille <address@hidden> a écrit :

> * doc/bison.texi (Type Generation): New section.

I will squash the following patch, to demonstrate the use
of api.value.type=union in the doc.  There is sill another
full example with %union, so I'm not removing anything here.

commit 12676d2f7739c3f5010840eae95d41a31b7bb93c
Author: Akim Demaille <address@hidden>
Date:   Mon Feb 25 12:03:30 2013 +0100

    squash! doc: api.value.type union.
    
    * doc/bison.texi (Multi-function Calc): Convert to use
    api.value.type=union.

diff --git a/doc/bison.texi b/doc/bison.texi
index f88b8d6..fd23963 100644
--- a/doc/bison.texi
+++ b/doc/bison.texi
@@ -2413,15 +2413,10 @@ Here are the C and Bison declarations for the 
multi-function calculator.
 address@hidden
 @end group
 
address@hidden
-%union @{
-  double    val;   /* For returning numbers.  */
-  symrec  *tptr;   /* For returning symbol-table pointers.  */
address@hidden
address@hidden group
-%token <val>  NUM        /* Simple double precision number.  */
-%token <tptr> VAR FNCT   /* Variable and function.  */
-%type  <val>  exp
+%define api.value.type union /* Generate YYSTYPE from these types:  */
+%token <double>  NUM         /* Simple double precision number.  */
+%token <symrec*> VAR FNCT    /* Symbol table pointer: variable and function.  
*/
+%type  <double>  exp
 
 @group
 %precedence '='
@@ -2436,23 +2431,23 @@ The above grammar introduces only two new features of 
the Bison language.
 These features allow semantic values to have various data types
 (@pxref{Multiple Types, ,More Than One Value Type}).
 
-The @code{%union} declaration specifies the entire list of possible types;
-this is instead of defining @code{api.value.type}.  The allowable types are now
-double-floats (for @code{exp} and @code{NUM}) and pointers to entries in
-the symbol table.  @xref{Union Decl, ,The Union Declaration}.
-
-Since values can now have various types, it is necessary to associate a
-type with each grammar symbol whose semantic value is used.  These symbols
-are @code{NUM}, @code{VAR}, @code{FNCT}, and @code{exp}.  Their
-declarations are augmented with information about their data type (placed
-between angle brackets).
-
-The Bison construct @code{%type} is used for declaring nonterminal
-symbols, just as @code{%token} is used for declaring token types.  We
-have not used @code{%type} before because nonterminal symbols are
-normally declared implicitly by the rules that define them.  But
address@hidden must be declared explicitly so we can specify its value type.
address@hidden Decl, ,Nonterminal Symbols}.
+The special @code{union} value assigned to the @code{%define} variable
address@hidden specifies that the symbols are defined with their data
+types.  Bison will generate an appropriate definition of @code{YYSTYPE} to
+store these values.
+
+Since values can now have various types, it is necessary to associate a type
+with each grammar symbol whose semantic value is used.  These symbols are
address@hidden, @code{VAR}, @code{FNCT}, and @code{exp}.  Their declarations are
+augmented with their data type (placed between angle brackets).  For
+instance, values of @code{NUM} are stored in @code{double}.
+
+The Bison construct @code{%type} is used for declaring nonterminal symbols,
+just as @code{%token} is used for declaring token types.  Previously we did
+not use @code{%type} before because nonterminal symbols are normally
+declared implicitly by the rules that define them.  But @code{exp} must be
+declared explicitly so we can specify its value type.  @xref{Type Decl,
+,Nonterminal Symbols}.
 
 @node Mfcalc Rules
 @subsection Grammar Rules for @code{mfcalc}
@@ -2676,11 +2671,18 @@ yylex (void)
   if (c == '.' || isdigit (c))
     @{
       ungetc (c, stdin);
-      scanf ("%lf", &yylval.val);
+      scanf ("%lf", &yylval.yytype_NUM);
       return NUM;
     @}
 @end group
address@hidden example
+
address@hidden
+Bison generated a definition of @code{YYSTYPE} with a member named
address@hidden to store value of @code{NUM} symbols.
 
address@hidden file: mfcalc.y: 3
address@hidden
 @group
   /* Char starts an identifier => read the name.       */
   if (isalpha (c))
@@ -2722,7 +2724,7 @@ yylex (void)
       s = getsym (symbuf);
       if (s == 0)
         s = putsym (symbuf, VAR);
-      yylval.tptr = s;
+      *((symrec**) &yylval) = s;
       return s->type;
     @}
 
@@ -9624,7 +9626,7 @@ prologue:
 /* Formatting semantic values.  */
 %printer @{ fprintf (yyoutput, "%s", $$->name); @} VAR;
 %printer @{ fprintf (yyoutput, "%s()", $$->name); @} FNCT;
-%printer @{ fprintf (yyoutput, "%g", $$); @} <val>;
+%printer @{ fprintf (yyoutput, "%g", $$); @} <double>;
 @end example
 
 The @code{%define} directive instructs Bison to generate run-time trace
@@ -9637,8 +9639,8 @@ ill-named) @code{%verbose} directive.
 The set of @code{%printer} directives demonstrates how to format the
 semantic value in the traces.  Note that the specification can be done
 either on the symbol type (e.g., @code{VAR} or @code{FNCT}), or on the type
-tag: since @code{<val>} is the type for both @code{NUM} and @code{exp}, this
-printer will be used for them.
+tag: since @code{<double>} is the type for both @code{NUM} and @code{exp},
+this printer will be used for them.
 
 Here is a sample of the information provided by run-time traces.  The traces
 are sent onto standard error.
@@ -9688,7 +9690,7 @@ Entering state 24
 
 @noindent
 The previous reduction demonstrates the @code{%printer} directive for
address@hidden<val>}: both the token @code{NUM} and the resulting nonterminal
address@hidden<double>}: both the token @code{NUM} and the resulting nonterminal
 @code{exp} have @samp{1} as value.
 
 @example