+2008-11-03 Akim Demaille <demaille@gostai.com>
+
+ Use variants to support objects as semantic values.
+ This patch was inspired by work by Michiel De Wilde. But he used Boost
+ variants which (i) requires Boost on the user side, (ii) is slow, and
+ (iii) has useless overhead (the parser knows the type of the semantic value
+ there is no reason to duplicate this information as Boost.Variants do).
+
+ This implementation reserves a buffer large enough to store the largest
+ objects. yy::variant implements this buffer. It was implemented with
+ Quentin Hocquet.
+
+ * src/output.c (type_names_output): New.
+ (output_skeleton): Invoke it.
+ * data/c++.m4 (b4_variant_if): New.
+ (b4_symbol_value): If needed, provide a definition for variants.
+ * data/lalr1.cc (b4_symbol_value, b4_symbol_action_)
+ (b4_symbol_variant, _b4_char_sizeof_counter, _b4_char_sizeof_dummy)
+ (b4_char_sizeof, yy::variant): New.
+ (parser::parse): If variants are requested, define
+ parser::union_type, parser::variant, change the definition of
+ semantic_type, construct $$ before running the user action instead
+ of performing a default $$ = $1.
+ * examples/variant.yy: New.
+ Based on an example by Michiel De Wilde.
+
2008-11-03 Akim Demaille <demaille@gostai.com>
Parameterize the extraction of semantic values.
Matt Kraai kraai@alumni.cmu.edu
Matt Rosing rosing@peakfive.com
Michael Hayes m.hayes@elec.canterbury.ac.nz
+Michiel De Wilde mdewilde.agilent@gmail.com
Mickael Labau labau_m@epita.fr
Mike Castle dalgoda@ix.netcom.com
Neil Booth NeilB@earthling.net
Peter Fales psfales@lucent.com
Peter Hamorsky hamo@upjs.sk
Piotr Gackiewicz gacek@intertel.com.pl
+Quentin Hocquet hocquet@gostai.com
Quoc Peyrot chojin@lrde.epita.fr
R Blake blakers@mac.com
Raja R Harinath harinath@cs.umn.edu
## Semantic Values. ##
## ----------------- ##
+# b4_variant_if([IF-VARIANT-ARE-USED], [IF-NOT])
+# ----------------------------------------------
+m4_define([b4_variant_if],
+[b4_percent_define_ifdef([[variant]], [$1], [$2])])
+
# b4_lhs_value([TYPE])
# --------------------
m4_include(b4_pkgdatadir/[c++.m4])
+# How the semantic value is extracted when using variants.
+b4_variant_if([
+ # b4_symbol_value(VAL, [TYPE])
+ # ----------------------------
+ m4_define([b4_symbol_value],
+ [m4_ifval([$2],
+ [$1.as<$2>()],
+ [$1])])
+]) # b4_variant_if
+
+
+# b4_symbol_action_(SYMBOL-TAG, SYMBOL-NUM, SYMBOL-TYPENAME)
+# ----------------------------------------------------------
+# Invoke b4_dollar_dollar(SYMBOL_TYPENAME) for each symbol.
+m4_define([b4_symbol_action_],
+[m4_ifval($3,
+[ case $2: // $1
+ b4_dollar_dollar($@);
+ break;
+])])
+
+
+# b4_symbol_variant(YYTYPE, YYVAL, ACTION)
+# ----------------------------------------
+# Run some ACTION ("build", or "destroy") on YYVAL of symbol type
+# YYTYPE.
+m4_define([b4_symbol_variant],
+[m4_pushdef([b4_dollar_dollar],
+ [$2.$3<$][3>()])dnl
+ switch ($1)
+ {
+m4_map([b4_symbol_action_], m4_defn([b4_type_names]))
+ default:
+ break;
+ }
+m4_popdef([b4_dollar_dollar])dnl
+])
+
+
+# _b4_char_sizeof_counter
+# -----------------------
+# A counter used by _b4_char_sizeof_dummy to create fresh symbols.
+m4_define([_b4_char_sizeof_counter],
+[0])
+
+# _b4_char_sizeof_dummy
+# ---------------------
+# At each call return a new C++ identifier.
+m4_define([_b4_char_sizeof_dummy],
+[m4_define([_b4_char_sizeof_counter], m4_incr(_b4_char_sizeof_counter))dnl
+dummy[]_b4_char_sizeof_counter])
+
+
+# b4_char_sizeof(SYMBOL-TAG, SYMBOL-NUM, SYMBOL-TYPENAME)
+# -------------------------------------------------------
+# To be mapped on the list of type names to produce:
+#
+# char dummy1[sizeof(type_name_1)];
+# char dummy2[sizeof(type_name_2)];
+#
+# for defined type names.
+# $3 is doubly-quoted, do not quote it again.
+m4_define([b4_char_sizeof],
+[m4_ifval($3,
+[
+ char _b4_char_sizeof_dummy@{sizeof($3)@}; // $1])dnl
+])
+
+
m4_define([b4_parser_class_name],
[b4_percent_define_get([[parser_class_name]])])
]b4_namespace_open[
class position;
class location;
+]b4_variant_if([[
+ /// A char[S] buffer to store and retrieve objects.
+ ///
+ /// Sort of a variant, but does not keep track of the nature
+ /// of the stored data, since that knowledge is available
+ /// via the current state.
+ template <size_t S>
+ struct variant
+ {
+ /// Instantiate a \a T in here.
+ template <typename T>
+ inline void
+ build()
+ {
+ new (buffer) T;
+ }
+
+ /// Destroy the stored \a T.
+ template <typename T>
+ inline void
+ destroy()
+ {
+ reinterpret_cast<T&>(buffer).~T();
+ }
+
+ /// Accessor to a built \a T.
+ template <typename T>
+ inline T&
+ as()
+ {
+ return reinterpret_cast<T&>(buffer);
+ }
+
+ /// Const accessor to a built \a T (for %printer).
+ template <typename T>
+ inline const T&
+ as() const
+ {
+ return reinterpret_cast<const T&>(buffer);
+ }
+
+ /// A buffer large enough to store any of the semantic values.
+ char buffer[S];
+ };
+]])[
]b4_namespace_close[
#include "location.hh"
class ]b4_parser_class_name[
{
public:
- /// Symbol semantic values.
#ifndef YYSTYPE
-]m4_ifdef([b4_stype],
+]b4_variant_if(
+[ /// An auxiliary type to compute the largest semantic type.
+ union union_type
+ {]m4_map([b4_char_sizeof], m4_defn([b4_type_names]))[
+ };
+
+ /// Symbol semantic values.
+ typedef variant<sizeof(union_type)> semantic_type;],
+[ /// Symbol semantic values.
+m4_ifdef([b4_stype],
[ union semantic_type
- {
-b4_user_stype
+ {b4_user_stype
};],
[m4_if(b4_tag_seen_flag, 0,
[[ typedef int semantic_type;]],
-[[ typedef YYSTYPE semantic_type;]])])[
+[[ typedef YYSTYPE semantic_type;]])])])[
#else
typedef YYSTYPE semantic_type;
#endif
/* Discard the token being shifted. */
yychar = yyempty_;
-
yysemantic_stack_.push (yylval);
yylocation_stack_.push (yylloc);
| yyreduce -- Do a reduction. |
`-----------------------------*/
yyreduce:
- yylen = yyr2_[yyn];
+ yylen = yyr2_[yyn];]b4_variant_if([
+ /* Variants are always initialized to an empty instance of the
+ correct type. The default $$=$1 rule is NOT applied when using
+ variants */
+ ]b4_symbol_variant([[yyr1_@{yyn@}]], [yyval], [build])[],[
/* If YYLEN is nonzero, implement the default value of the action:
`$$ = $1'. Otherwise, use the top of the stack.
if (yylen)
yyval = yysemantic_stack_@{yylen - 1@};
else
- yyval = yysemantic_stack_@{0@};
+ yyval = yysemantic_stack_@{0@};])[
{
slice<location_type, location_stack_type> slice (yylocation_stack_, yylen);
yypop_ (yylen);
yylen = 0;
YY_STACK_PRINT ();
-
yysemantic_stack_.push (yyval);
yylocation_stack_.push (yyloc);
--- /dev/null
+/* Test file for C++ parsers using variants.
+ Based on an example by Michiel De Wilde <mdewilde.agilent@gmail.com>. */
+%language "C++"
+%debug
+%defines
+%define variant
+
+%code requires // *.hh
+{
+#include <string>
+}
+
+%code // *.cc
+{
+#include <algorithm>
+#include <iostream>
+#include <sstream>
+
+static yy::parser::token_type yylex(yy::parser::semantic_type* yylval);
+}
+
+%token <std::string> TEXT
+%token <int> NUMBER
+%printer { debug_stream() << $$; } <int> <std::string>
+%token END_OF_FILE 0
+
+%type <std::string> text result
+
+%%
+
+result:
+ text { std::cout << $1 << std::endl; }
+;
+
+text:
+ /* nothing */ { /* This will generate an empty string */ }
+| text TEXT { std::swap($$,$1); $$.append($2); }
+| text NUMBER {
+ std::swap($$,$1);
+ std::ostringstream o;
+ o << ' ' << $2;
+ $$.append(o.str());
+ }
+;
+%%
+
+// The yylex function providing subsequent tokens:
+// TEXT "I have three numbers for you:"
+// NUMBER 1
+// NUMBER 2
+// NUMBER 3
+// TEXT " and that's all!"
+// END_OF_FILE
+
+static
+yy::parser::token_type
+yylex(yy::parser::semantic_type* yylval)
+{
+ static int stage = 0;
+ yy::parser::token_type result;
+
+ switch (stage)
+ {
+ case 0:
+ yylval->build<std::string>();
+ yylval->as<std::string>() = std::string("I have three numbers for you:");
+ result = yy::parser::token::TEXT;
+ break;
+ case 1:
+ case 2:
+ case 3:
+ yylval->build<int>();
+ yylval->as<int>() = stage;
+ result = yy::parser::token::NUMBER;
+ break;
+ case 4:
+ yylval->build<std::string>();
+ yylval->as<std::string>() = std::string(" and that's all!");
+ result = yy::parser::token::TEXT;
+ break;
+ default:
+ result = yy::parser::token::END_OF_FILE;
+ break;
+ }
+
+ stage++;
+ return result;
+}
+
+// Mandatory error function
+void
+yy::parser::error(const yy::parser::location_type& yylloc,
+ const std::string& message)
+{
+ std::cerr << yylloc << ": " << message << std::endl;
+}
+
+int
+main(int argc, char *argv[])
+{
+ yy::parser p;
+ p.set_debug_level(!!getenv("YYDEBUG"));
+ p.parse();
+}
+
+// Local Variables:
+// mode: C++
+// End:
+/*-----------------------------------------------.
+| For each symbol type, its tags and type name. |
+`-----------------------------------------------*/
+
+static void
+type_names_output (FILE *out)
+{
+ int i;
+ char const *sep = "";
+
+ fputs ("m4_define([b4_type_names],\n[", out);
+ for (i = 0; i < nsyms; ++i)
+ {
+ symbol *sym = symbols[i];
+ /* Symbol-name, Symbol-number, optional typename. */
+ fprintf (out, "%s[", i ? ",\n" : "");
+ escaped_output (out, sym->tag);
+ fprintf (out, ", %d, [[%s]]]",
+ sym->number,
+ sym->type_name ? sym->type_name : "");
+ }
+ fputs ("])\n\n", out);
+}
+
+
/*---------------------------------.
| Output the user actions to OUT. |
`---------------------------------*/
muscle_insert_unsigned_int_table ("conflicting_rules", conflict_list,
0, 1, conflict_list_cnt);
}
-
\f
/*---------------------------.
| Call the skeleton parser. |
/* Output the definitions of all the muscles. */
fputs ("m4_init()\n", out);
+ type_names_output (out);
user_actions_output (out);
merger_output (out);
token_definitions_output (out);
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