-*- outline -*-
+
+* URGENT: Prologue
+The %union is declared after the user C declarations. It can be
+a problem if YYSTYPE is declared after the user part.
+
+Actually, the real problem seems that the %union ought to be output
+where it was defined. For instance, in gettext/intl/plural.y, we
+have:
+
+ %{
+ ...
+ #include "gettextP.h"
+ ...
+ %}
+
+ %union {
+ unsigned long int num;
+ enum operator op;
+ struct expression *exp;
+ }
+
+ %{
+ ...
+ static int yylex PARAMS ((YYSTYPE *lval, const char **pexp));
+ ...
+ %}
+
+Where the first part defines struct expression, the second uses it to
+define YYSTYPE, and the last uses YYSTYPE. Only this order is valid.
+
+Note that we have the same problem with GCC.
+
+I suggest splitting the prologue into pre-prologue and post-prologue.
+The reason is that:
+
+1. we keep language independance as it is the skeleton that joins the
+two prologues (there is no need for the engine to encode union yystype
+and to output it inside the prologue, which breaks the language
+independance of the generator)
+
+2. that makes it possible to have several %union in input. I think
+this is a pleasant (but useless currently) feature, but in the future,
+I want a means to %include other bits of grammars, and _then_ it will
+be important for the various bits to define their needs in %union.
+
+When implementing multiple-%union support, bare the following in mind:
+
+- when --yacc, this must be flagged as an error. Don't make it fatal
+ though.
+
+- The #line must now appear *inside* the definition of yystype.
+ Something like
+
+ {
+ #line 12 "foo.y"
+ int ival;
+ #line 23 "foo.y"
+ char *sval;
+ }
+
+* Language independent actions
+
+Currently bison, the generator, transforms $1, $$ and so forth into
+direct C code, manipulating the stacks. This is problematic, because
+(i) it means that if we want more languages, we need to update the
+generator, and (ii), it forces names everywhere (e.g., the C++
+skeleton would be happy to use other naming schemes, and actually,
+even other accessing schemes).
+
+Therefore we want
+
+1. the generator to replace $1, etc. by M4 macro invocations
+ (b4_dollar(1), b4_at(3), b4_dollar_dollar) etc.
+
+2. the skeletons to define these macros.
+
+But currently the actions are double-quoted, to protect them from M4
+evaluation. So we need to:
+
+3. stop quoting them
+
+4. change the [ and ] in the actions into @<:@ and @:>@
+
+5. extend the postprocessor to maps these back onto [ and ].
+
* Coding system independence
Paul notes:
#define BAR 257
...
-> I'm in favor of
->
-> %token FOO 256
-> %token BAR 257
->
-> and Bison moves error into 258.
-
-Yes, I think that's a valid extension too, if the user doesn't define
-the token number for error.
-
* Output directory
Akim:
error token etc., we often throw away yylval without giving a chance
of cleaning it up to the user.
-* NEWS
-Sort from 1.31 NEWS.
-
-* Prologue
-The %union is declared after the user C declarations. It can be
-a problem if YYSTYPE is declared after the user part. []
-
-Actually, the real problem seems that the %union ought to be output
-where it was defined. For instance, in gettext/intl/plural.y, we
-have:
-
- %{
- ...
- #include "gettextP.h"
- ...
- %}
-
- %union {
- unsigned long int num;
- enum operator op;
- struct expression *exp;
- }
-
- %{
- ...
- static int yylex PARAMS ((YYSTYPE *lval, const char **pexp));
- ...
- %}
-
-Where the first part defines struct expression, the second uses it to
-define YYSTYPE, and the last uses YYSTYPE. Only this order is valid.
-
-Note that we have the same problem with GCC.
-
* --graph
Show reductions. []
be invoked after the action. For reasons of symmetry I also added
YYACT_PROLOGUE. Although I had no use for that I can envision how it
might come in handy for debugging purposes.
-All is needed is to add
+All is needed is to add
#if YYLSP_NEEDED
YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen, yyloc, (yylsp - yylen));
projects / bison.git / blobdiff