+# b4_sync_start(LINE, FILE)
+# -------------------------
+m4_define([b4_sync_start], [[#]line $1 $2])
+
+
+## -------------- ##
+## User actions. ##
+## -------------- ##
+
+# b4_case(LABEL, STATEMENTS)
+# --------------------------
+m4_define([b4_case],
+[ case $1:
+$2
+b4_syncline([@oline@], [@ofile@])
+ break;])
+
+
+# b4_predicate_case(LABEL, CONDITIONS)
+# ------------------------------------
+m4_define([b4_predicate_case],
+[ case $1:
+ if (! ($2)) YYERROR;
+b4_syncline([@oline@], [@ofile@])
+ break;])
+
+
+# b4_yydestruct_define
+# --------------------
+# Define the "yydestruct" function.
+m4_define_default([b4_yydestruct_define],
+[[/*-----------------------------------------------.
+| Release the memory associated to this symbol. |
+`-----------------------------------------------*/
+
+]b4_function_define([yydestruct],
+ [static void],
+ [[const char *yymsg], [yymsg]],
+ [[int yytype], [yytype]],
+ [[YYSTYPE *yyvaluep], [yyvaluep]][]dnl
+b4_locations_if( [, [[YYLTYPE *yylocationp], [yylocationp]]])[]dnl
+m4_ifset([b4_parse_param], [, b4_parse_param]))[
+{
+]b4_parse_param_use([yyvaluep], [yylocationp])dnl
+[ if (!yymsg)
+ yymsg = "Deleting";
+ YY_SYMBOL_PRINT (yymsg, yytype, yyvaluep, yylocationp);
+
+ YY_IGNORE_MAYBE_UNINITIALIZED_BEGIN
+ ]b4_symbol_actions([destructor])[
+ YY_IGNORE_MAYBE_UNINITIALIZED_END
+}]dnl
+])
+
+
+# b4_yy_symbol_print_define
+# -------------------------
+# Define the "yy_symbol_print" function.
+m4_define_default([b4_yy_symbol_print_define],
+[[
+/*----------------------------------------.
+| Print this symbol's value on YYOUTPUT. |
+`----------------------------------------*/
+
+]b4_function_define([yy_symbol_value_print],
+ [static void],
+ [[FILE *yyoutput], [yyoutput]],
+ [[int yytype], [yytype]],
+ [[YYSTYPE const * const yyvaluep], [yyvaluep]][]dnl
+b4_locations_if([, [[YYLTYPE const * const yylocationp], [yylocationp]]])[]dnl
+m4_ifset([b4_parse_param], [, b4_parse_param]))[
+{
+ FILE *yyo = yyoutput;
+]b4_parse_param_use([yyo], [yylocationp])dnl
+[ if (!yyvaluep)
+ return;]
+dnl glr.c does not feature yytoknum.
+m4_if(b4_skeleton, ["yacc.c"],
+[[# ifdef YYPRINT
+ if (yytype < YYNTOKENS)
+ YYPRINT (yyoutput, yytoknum[yytype], *yyvaluep);
+# endif
+]])dnl
+ b4_symbol_actions([printer])[
+}
+
+
+/*--------------------------------.
+| Print this symbol on YYOUTPUT. |
+`--------------------------------*/
+
+]b4_function_define([yy_symbol_print],
+ [static void],
+ [[FILE *yyoutput], [yyoutput]],
+ [[int yytype], [yytype]],
+ [[YYSTYPE const * const yyvaluep], [yyvaluep]][]dnl
+b4_locations_if([, [[YYLTYPE const * const yylocationp], [yylocationp]]])[]dnl
+m4_ifset([b4_parse_param], [, b4_parse_param]))[
+{
+ YYFPRINTF (yyoutput, "%s %s (",
+ yytype < YYNTOKENS ? "token" : "nterm", yytname[yytype]);
+
+]b4_locations_if([ YY_LOCATION_PRINT (yyoutput, *yylocationp);
+ YYFPRINTF (yyoutput, ": ");
+])dnl
+[ yy_symbol_value_print (yyoutput, yytype, yyvaluep]dnl
+b4_locations_if([, yylocationp])[]b4_user_args[);
+ YYFPRINTF (yyoutput, ")");
+}]dnl
+])
+
+
+## ---------------- ##
+## api.value.type. ##
+## ---------------- ##
+
+
+# ---------------------- #
+# api.value.type=union. #
+# ---------------------- #
+
+# b4_symbol_type_register(SYMBOL-NUM)
+# -----------------------------------
+# Symbol SYMBOL-NUM has a type (for variant) instead of a type-tag.
+# Extend the definition of %union's body with a field of that type,
+# and extend the symbol's "type" field to point to the field name,
+# instead of the type name.
+m4_define([b4_symbol_type_register],
+[m4_define([b4_symbol($1, type_tag)],
+ [b4_symbol_if([$1], [has_id],
+ [b4_symbol([$1], [id])],
+ [yytype_[]b4_symbol([$1], [number])])])dnl
+m4_append([b4_user_union_members],
+m4_expand([
+ b4_symbol_tag_comment([$1])dnl
+ b4_symbol([$1], [type]) b4_symbol([$1], [type_tag]);]))
+])
+
+
+# b4_type_define_tag(SYMBOL1-NUM, ...)
+# ------------------------------------
+# For the batch of symbols SYMBOL1-NUM... (which all have the same
+# type), enhance the %union definition for each of them, and set
+# there "type" field to the field tag name, instead of the type name.
+m4_define([b4_type_define_tag],
+[b4_symbol_if([$1], [has_type],
+ [m4_map([b4_symbol_type_register], [$@])])
+])
+
+
+# b4_symbol_value_union(VAL, [TYPE])
+# ----------------------------------
+# Same of b4_symbol_value, but when api.value.type=union.
+m4_define([b4_symbol_value_union],
+[m4_ifval([$2],
+ [(*($2*)(&$1))],
+ [$1])])
+])
+
+
+# b4_value_type_setup_union
+# -------------------------
+# Setup support for api.value.type=union. Symbols are defined with a
+# type instead of a union member name: build the corresponding union,
+# and give the symbols their tag.
+m4_define([b4_value_type_setup_union],
+[m4_define([b4_union_members])
+b4_type_foreach([b4_type_define_tag])
+m4_copy_force([b4_symbol_value_union], [b4_symbol_value])
+])
+
+
+# ---------------- #
+# api.value.type. #
+# ---------------- #
+
+
+# b4_value_type_setup_variant
+# ---------------------------
+# Setup support for api.value.type=variant. By default, fail, specialized
+# by other skeletons.
+m4_define([b4_value_type_setup_variant],
+[b4_complain_at(b4_percent_define_get_loc([[api.value.type]]),
+ [['%s' does not support '%s']],
+ [b4_skeleton],
+ [%define api.value.type variant])])
+
+
+# _b4_value_type_setup_keyword
+# ----------------------------
+# api.value.type is defined with a keyword/string syntax. Check if
+# that is properly defined, and prepare its use.
+m4_define([_b4_value_type_setup_keyword],
+[b4_percent_define_check_values([[[[api.value.type]],
+ [[none]],
+ [[union]],
+ [[union-directive]],
+ [[variant]],
+ [[yystype]]]])dnl
+m4_case(b4_percent_define_get([[api.value.type]]),
+ [union], [b4_value_type_setup_union],
+ [variant], [b4_value_type_setup_variant])])
+
+
+# b4_value_type_setup
+# -------------------
+# Check if api.value.type is properly defined, and possibly prepare
+# its use.
+b4_define_silent([b4_value_type_setup],
+[# Define default value.
+b4_percent_define_ifdef([[api.value.type]], [],
+[# %union => api.value.type=union-directive
+m4_ifdef([b4_union_members],
+[m4_define([b4_percent_define_kind(api.value.type)], [keyword])
+m4_define([b4_percent_define(api.value.type)], [union-directive])],
+[# no tag seen => api.value.type={int}
+m4_if(b4_tag_seen_flag, 0,
+[m4_define([b4_percent_define_kind(api.value.type)], [code])
+m4_define([b4_percent_define(api.value.type)], [int])],
+[# otherwise api.value.type=yystype
+m4_define([b4_percent_define_kind(api.value.type)], [keyword])
+m4_define([b4_percent_define(api.value.type)], [yystype])])])])
+
+# Set up.
+m4_bmatch(b4_percent_define_get_kind([[api.value.type]]),
+ [keyword\|string], [_b4_value_type_setup_keyword])
+])
+
+
+## -------------- ##
+## Declarations. ##
+## -------------- ##
+
+
+# b4_value_type_define
+# --------------------
+m4_define([b4_value_type_define],
+[b4_value_type_setup[]dnl
+/* Value type. */
+m4_bmatch(b4_percent_define_get_kind([[api.value.type]]),
+[code],
+[[#if ! defined ]b4_api_PREFIX[STYPE && ! defined ]b4_api_PREFIX[STYPE_IS_DECLARED
+typedef ]b4_percent_define_get([[api.value.type]])[ ]b4_api_PREFIX[STYPE;
+# define ]b4_api_PREFIX[STYPE_IS_TRIVIAL 1
+# define ]b4_api_PREFIX[STYPE_IS_DECLARED 1
+#endif
+]],
+[m4_bmatch(b4_percent_define_get([[api.value.type]]),
+[union\|union-directive],
+[[#if ! defined ]b4_api_PREFIX[STYPE && ! defined ]b4_api_PREFIX[STYPE_IS_DECLARED
+typedef union ]b4_union_name[ ]b4_api_PREFIX[STYPE;
+union ]b4_union_name[
+{
+]b4_user_union_members[
+};
+# define ]b4_api_PREFIX[STYPE_IS_TRIVIAL 1
+# define ]b4_api_PREFIX[STYPE_IS_DECLARED 1
+#endif
+]])])])
+