Re: X3: How to write generic rules

On 27-01-16 21:27, Mike Gresens wrote:
> Hi,
>
> lets say you have:
>
> user_rule = ...
> user_rule_def = ...
>
> group_rule = ...
> group_rule_def = ...
>
> BOOST_SPIRIT_DEFINE(user_rule, group_rule)
>
> Now you want to make a generic list_of_rule:
>
> list_of_rule = ??? MAGIC ???
>
> So you can use it later:
>
> users_rule_def = list_of_rule<user_rule>
> groups_rule_def = list_of_rule<groups_rule>
>
> How to do that?
>
How about:

    auto list_of = [](auto p) { return x3::as_parser(p) % ","; };

    auto user_rule   = "user"  >> x3::int_;
    auto group_rule  = "group" >> x3::bool_;

    auto users_rule  = list_of(user_rule);
    auto groups_rule = list_of(group_rule);

I wouldn't overcomplicate things in X3.
You can always look at operator/list.hpp or directive/repeat.hpp to see
how these directives were made.

Here's a simple test: http://melpon.org/wandbox/permlink/m87LpfTAmATGxcyz

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#include <boost/spirit/home/x3.hpp>
#include <iostream>

namespace Parsing
{
    namespace x3 = boost::spirit::x3;

    auto list_of = [](auto p) { return x3::as_parser(p) % ","; };

    auto user_rule   = "user"  >> x3::int_;
    auto group_rule  = "group" >> x3::bool_;

    auto users_rule  = list_of(user_rule);
    auto groups_rule = list_of(group_rule);
}

template <typename T, typename P>
void test(std::string const& input, P const& parser) {
    auto f = input.begin();
    auto l = input.end();

    std::vector<T> into;
    bool ok = parse(f, l, parser, into);
    if (ok) {
        std::cout << "Parsed into: ";
        std::copy(into.begin(), into.end(), std::ostream_iterator<T>(std::cout, " "));
        std::cout << "\n";
    } else {
        std::cout << "Parsed failed";
    }

    if (f != l) {
        std::cout << "Remaining input: '" << std::string(f,l) << "'\n-----\n";
    }
}

int main()
{
    std::cout << std::boolalpha;

    test<int>("user1,user2,user42", Parsing::users_rule);
    test<bool>("grouptrue,grouptrue,groupfalse", Parsing::groups_rule);
}