How to refer to value from symbol table? - c++

Question

I can't figure out how to pass value from symbol table into the function.
template <typename Iterator>
class single_attribute_grammar : public qi::grammar<Iterator, AttributeData(), qi::blank_type>
{
public:
single_attribute_grammar(const word_symbols &words) : single_attribute_grammar::base_type(single_attribute_rule)
{
auto attr_word = phx::bind(&AttributeData::word, qi::_val);
auto grammar_word = phx::bind(&WordGrammar::word, qi::_1);
auto attr_value = phx::bind(&AttributeData::value, qi::_val);
single_attribute_rule = qi::lexeme[words[attr_word = grammar_word] >
qi::int_[attr_value = qi::_1] > (qi::space|qi::eoi)] >>
qi::eps(phx::bind(verify_range, qi::_r1, qi::_val)); // <-- HERE is the problem
BOOST_SPIRIT_DEBUG_NODE(single_attribute_rule);
}
private:
qi::rule<Iterator, AttributeData(), qi::blank_type> single_attribute_rule;
};
I would think I can refer to the value of the found key using qi::_r1 but the code doesn't compile:
main.cpp:72:31: required from ‘single_attribute_grammar<Iterator>::single_attribute_grammar(const word_symbols&) [with Iterator = boost::spirit::classic::position_iterator2<boost::spirit::multi_pass<std::istreambuf_iterator<char, std::char_traits<char> > > >; word_symbols = boost::spirit::qi::symbols<char, WordGrammar>]’
main.cpp:87:16: required from ‘all_attributes_grammar<Iterator>::all_attributes_grammar(const word_symbols&) [with Iterator = boost::spirit::classic::position_iterator2<boost::spirit::multi_pass<std::istreambuf_iterator<char, std::char_traits<char> > > >; word_symbols = boost::spirit::qi::symbols<char, WordGrammar>]’
main.cpp:130:62: required from here
/usr/include/boost/spirit/home/support/context.hpp:180:13: error: static assertion failed: index_is_out_of_bounds
BOOST_SPIRIT_ASSERT_MSG(
^
In file included from /usr/include/boost/spirit/home/qi/domain.hpp:18:0,
from /usr/include/boost/spirit/home/qi/meta_compiler.hpp:15,
from /usr/include/boost/spirit/home/qi/action/action.hpp:14,
from /usr/include/boost/spirit/home/qi/action.hpp:14,
from /usr/include/boost/spirit/home/qi.hpp:14,
from /usr/include/boost/spirit/include/qi.hpp:16,
from main.cpp:11:
/usr/include/boost/spirit/home/support/context.hpp:186:13: error: no type named ‘type’ in ‘struct boost::fusion::result_of::at_c<boost::fusion::cons<AttributeData&, boost::fusion::nil_>, 1>’
type;
^~~~
In case it's helpful here is the MVCE.
#include <iomanip>
#include <string>
#include <vector>
#include <boost/variant.hpp>
#include <boost/optional/optional.hpp>
#define BOOST_SPIRIT_DEBUG
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/qi_symbols.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_object.hpp> // construct
#include <boost/spirit/include/support_multi_pass.hpp>
#include <boost/spirit/include/classic_position_iterator.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/phoenix/bind.hpp>
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
namespace classic = boost::spirit::classic;
namespace phx = boost::phoenix;
namespace fusion = boost::fusion;
struct AttributeData
{
std::string word;
int value;
};
using AttributeVariant = boost::variant<
AttributeData
>;
struct WordGrammar
{
std::string word;
int range_from;
int range_to;
};
BOOST_FUSION_ADAPT_STRUCT(
AttributeData,
(std::string, word)
(int, value)
)
using word_symbols = qi::symbols<char, WordGrammar>;
bool verify_range(const WordGrammar &grammar, const AttributeData &data)
{
if(data.value < grammar.range_from || data.value > grammar.range_to)
{
return false;
}
return true;
}
template <typename Iterator>
class single_attribute_grammar : public qi::grammar<Iterator, AttributeData(), qi::blank_type>
{
public:
single_attribute_grammar(const word_symbols &words) : single_attribute_grammar::base_type(single_attribute_rule)
{
auto attr_word = phx::bind(&AttributeData::word, qi::_val);
auto grammar_word = phx::bind(&WordGrammar::word, qi::_1);
auto attr_value = phx::bind(&AttributeData::value, qi::_val);
single_attribute_rule = qi::lexeme[words[attr_word = grammar_word] >
qi::int_[attr_value = qi::_1] > (qi::space|qi::eoi)] >>
qi::eps(phx::bind(verify_range, qi::_r1, qi::_val)); // <-- HERE is the problem
BOOST_SPIRIT_DEBUG_NODE(single_attribute_rule);
}
private:
qi::rule<Iterator, AttributeData(), qi::blank_type> single_attribute_rule;
};
template <typename Iterator>
class all_attributes_grammar : public qi::grammar<Iterator, std::vector<AttributeVariant>(), qi::blank_type>
{
public:
all_attributes_grammar(const word_symbols &words) : all_attributes_grammar::base_type(line_attribute_vec_rule)
, sag(words)
{
line_attribute_rule = (
sag
);
BOOST_SPIRIT_DEBUG_NODE(line_attribute_rule);
line_attribute_vec_rule = (line_attribute_rule % *qi::blank) > qi::eoi;
BOOST_SPIRIT_DEBUG_NODE(line_attribute_vec_rule);
}
private:
single_attribute_grammar<Iterator> sag;
qi::rule<Iterator, AttributeVariant(), qi::blank_type> line_attribute_rule;
qi::rule<Iterator, std::vector<AttributeVariant>(), qi::blank_type> line_attribute_vec_rule;
};
int main()
{
std::vector<AttributeVariant> value;
std::string data{"N100 X-100 AC5"};
std::istringstream input(data);
// iterate over stream input
typedef std::istreambuf_iterator<char> base_iterator_type;
base_iterator_type in_begin(input);
// convert input iterator to forward iterator, usable by spirit parser
typedef boost::spirit::multi_pass<base_iterator_type> forward_iterator_type;
forward_iterator_type fwd_begin = boost::spirit::make_default_multi_pass(in_begin);
forward_iterator_type fwd_end;
// wrap forward iterator with position iterator, to record the position
typedef classic::position_iterator2<forward_iterator_type> pos_iterator_type;
pos_iterator_type position_begin(fwd_begin, fwd_end);
pos_iterator_type position_end;
word_symbols sym;
sym.add
("N", {"N", 1, 9999})
("X", {"X", -999, 999})
("AC", {"AC", -99, 999})
;
all_attributes_grammar<pos_iterator_type> all_attr_gr(sym);
try
{
qi::phrase_parse(position_begin, position_end, all_attr_gr, qi::blank, value);
}
catch (const qi::expectation_failure<pos_iterator_type>& e)
{
const classic::file_position_base<std::string>& pos = e.first.get_position();
std::cout <<
"Parse error at line " << pos.line << " column " << pos.column << ":" << std::endl <<
"'" << e.first.get_currentline() << "'" << std::endl <<
std::setw(pos.column) << " " << "^- here" << std::endl;
}
return 0;
}
Any ideas?

Answer 1

Lots of things to be simplified.
why is AttributeData adapted, when you use semantic actions instead? (see Boost Spirit: "Semantic actions are evil"?)
skipping whitespace is much more elegant when using a skipper. It's also logically contradictory to skip whitespace inside a lexeme (see Boost spirit skipper issues)
In particular, the skipping of whitespace here:
line_attribute_vec_rule = (line_attribute_rule % *qi::blank) > qi::eoi;
is completely impotent (because blanks are already skipped, the *qi::blank will never match any characters). The whole thing reduces to +line_attribute_rule.
line_attribute_vec_rule = +line_attribute_rule > qi::eoi;
Re: your answer
Indeed, you can use more state in the rule. Instead, I'd simplify the AST to support your case. Say:
struct AttrDef {
std::string word;
std::pair<int,int> range;
};
struct AttributeData {
AttrDef def;
int value;
bool is_valid() const {
return std::minmax({value, def.range.first, def.range.second}) == def.range;
}
};
BOOST_FUSION_ADAPT_STRUCT(AttributeData, def, value)
Now, single_attribute_grammar would not care about skipping, and be like:
using attr_defs = qi::symbols<char, AttrDef>;
template <typename Iterator>
struct single_attribute_grammar : public qi::grammar<Iterator, AttributeData()> {
single_attribute_grammar(const attr_defs &defs)
: single_attribute_grammar::base_type(start)
{
using namespace qi;
attribute_data = defs >> int_;
start %= attribute_data [ _pass = is_valid_(_1) ];
BOOST_SPIRIT_DEBUG_NODES((attribute_data));
}
private:
phx::function<std::function<bool(AttributeData const&)> > is_valid_ {&AttributeData::is_valid};
qi::rule<Iterator, AttributeData()> attribute_data;
qi::rule<Iterator, AttributeData()> start;
};
As you can see, there's no state because I didn't use eps. That's right, I flew right in the face of my own guideline ("avoid semantic actions") for the simple reason that it avoids explicit state (instead using the exsting qi::_pass).
Doing a lot of simplifications in main (specifically, using boost::spirit::istream_iterator rather than roll-your-own multi-pass adapting), I would arrive at this:
Live On Coliru
//#define BOOST_SPIRIT_DEBUG
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/classic_position_iterator.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
#include <iomanip>
namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;
struct AttrDef {
std::string word;
std::pair<int,int> range;
};
struct AttributeData {
AttrDef def;
int value;
bool is_valid() const {
return std::minmax({value, def.range.first, def.range.second}) == def.range;
}
};
BOOST_FUSION_ADAPT_STRUCT(AttributeData, def, value)
static inline std::ostream& operator<<(std::ostream& os, const AttrDef& def) {
return os << "AttrDef(" << def.word << ", " << def.range.first << ", " << def.range.second << ")";
}
using attr_defs = qi::symbols<char, AttrDef>;
template <typename Iterator>
struct single_attribute_grammar : public qi::grammar<Iterator, AttributeData()> {
single_attribute_grammar(const attr_defs &defs)
: single_attribute_grammar::base_type(start)
{
using namespace qi;
attribute_data = defs >> int_;
start %= attribute_data [ _pass = is_valid_(_1) ];
BOOST_SPIRIT_DEBUG_NODES((attribute_data));
}
private:
phx::function<std::function<bool(AttributeData const&)> > is_valid_ {&AttributeData::is_valid};
qi::rule<Iterator, AttributeData()> attribute_data;
qi::rule<Iterator, AttributeData()> start;
};
using AttributeVariant = boost::variant<AttributeData>;
template <typename Iterator>
class all_attributes_grammar : public qi::grammar<Iterator, std::vector<AttributeVariant>(), qi::blank_type>
{
public:
all_attributes_grammar(const attr_defs &defs)
: all_attributes_grammar::base_type(line_attribute_vec_rule),
sag(defs)
{
line_attribute_rule = (
sag
);
line_attribute_vec_rule = +line_attribute_rule > qi::eoi;
BOOST_SPIRIT_DEBUG_NODES((line_attribute_rule)(line_attribute_vec_rule));
}
private:
single_attribute_grammar<Iterator> sag;
qi::rule<Iterator, AttributeVariant()> line_attribute_rule;
qi::rule<Iterator, std::vector<AttributeVariant>(), qi::blank_type> line_attribute_vec_rule;
};
int main() {
constexpr bool fail = false, succeed = true;
struct _ { bool expect; std::string data; } const tests[] = {
{ succeed, "N100 X-100 AC5" },
{ fail, "" },
{ fail, " " },
{ succeed, "N1" },
{ succeed, " N1" },
{ succeed, "N1 " },
{ succeed, " N1 " },
{ fail, "N 1" },
{ fail, "N0" },
{ succeed, "N9999" },
{ fail, "N10000" },
};
for (auto test : tests) {
std::istringstream input(test.data);
typedef boost::spirit::classic::position_iterator2<boost::spirit::istream_iterator> pos_iterator_type;
pos_iterator_type position_begin(boost::spirit::istream_iterator{input >> std::noskipws}, {}), position_end;
attr_defs sym;
sym.add
("N", {"N", {1, 9999}})
("X", {"X", {-999, 999}})
("AC", {"AC", {-99, 999}})
;
all_attributes_grammar<pos_iterator_type> all_attr_gr(sym);
try {
std::vector<AttributeVariant> value;
std::cout << " --------- '" << test.data << "'\n";
bool actual = qi::phrase_parse(position_begin, position_end, all_attr_gr, qi::blank, value);
std::cout << ((test.expect == actual)?"PASS":"FAIL");
if (actual) {
std::cout << "\t";
for (auto& attr : value)
std::cout << boost::fusion::as_vector(boost::get<AttributeData>(attr)) << " ";
std::cout << "\n";
} else {
std::cout << "\t(no valid parse)\n";
}
}
catch (const qi::expectation_failure<pos_iterator_type>& e) {
auto& pos = e.first.get_position();
std::cout <<
"Parse error at line " << pos.line << " column " << pos.column << ":" << std::endl <<
"'" << e.first.get_currentline() << "'" << std::endl <<
std::setw(pos.column) << " " << "^- here" << std::endl;
}
if (position_begin != position_end)
std::cout << " -> Remaining '" << std::string(position_begin, position_end) << "'\n";
}
}
Prints:
--------- 'N100 X-100 AC5'
PASS (AttrDef(N, 1, 9999) 100) (AttrDef(X, -999, 999) -100) (AttrDef(AC, -99, 999) 5)
--------- ''
PASS (no valid parse)
--------- ' '
PASS (no valid parse)
-> Remaining ' '
--------- 'N1'
PASS (AttrDef(N, 1, 9999) 1)
--------- ' N1'
PASS (AttrDef(N, 1, 9999) 1)
--------- 'N1 '
PASS (AttrDef(N, 1, 9999) 1)
--------- ' N1 '
PASS (AttrDef(N, 1, 9999) 1)
--------- 'N 1'
PASS (no valid parse)
-> Remaining 'N 1'
--------- 'N0'
PASS (no valid parse)
-> Remaining 'N0'
--------- 'N9999'
PASS (AttrDef(N, 1, 9999) 9999)
--------- 'N10000'
PASS (no valid parse)
-> Remaining 'N10000'

Answer 2

After a bit more studying of boost spirit I've found the solution is to use locals and inherited attributes:
template <typename Iterator>
class single_attribute_grammar : public qi::grammar<Iterator, AttributeData(), qi::locals<WordGrammar>, qi::blank_type>
{
public:
single_attribute_grammar(const word_symbols &words) : single_attribute_grammar::base_type(single_attribute_rule)
{
auto attr_word = phx::bind(&AttributeData::word, qi::_val);
auto grammar_word = phx::bind(&WordGrammar::word, qi::_1);
auto attr_value = phx::bind(&AttributeData::value, qi::_val);
word_rule = words;
BOOST_SPIRIT_DEBUG_NODE(word_rule);
range_check_rule = qi::eps(phx::bind(verify_range, qi::_r1, qi::_r2));
BOOST_SPIRIT_DEBUG_NODE(range_check_rule);
single_attribute_rule = qi::lexeme[word_rule[attr_word = grammar_word,qi::_a=qi::_1] >
qi::int_[attr_value = qi::_1] > (qi::space|qi::eoi)] >>
range_check_rule(qi::_a, qi::_val);
BOOST_SPIRIT_DEBUG_NODE(single_attribute_rule);
}
private:
qi::rule<Iterator, WordGrammar()> word_rule;
qi::rule<Iterator, void(const WordGrammar&, const AttributeData&), qi::blank_type> range_check_rule;
qi::rule<Iterator, AttributeData(), qi::locals<WordGrammar>, qi::blank_type> single_attribute_rule;
};
Also because I use BOOST_SPIRIT_DEBUG_NODE overloading of stream operator for WordGrammar is necessary:
std::ostream& operator<<(std::ostream& ostr, const WordGrammar& grammar)
{
ostr << "WordGrammar(" << grammar.word << ", " << grammar.range_from << ", " << grammar.range_to << ")";
return ostr;
}