eval.h

 
#pragma once
 
#include "json_helpers.h"
#include "string_ops.h"
#include <format>
#include <variant>
#include "span.h"
 
namespace ghassanpl::eval
{

    using json = nlohmann::json;
    static inline const json null_json;

    struct value
    {
        std::variant<json, json*, json const*> v;
 
        value() noexcept = default;
        value(value const&) noexcept = default;
        value(value&&) noexcept = default;
        value& operator=(value const&) noexcept = default;
        value& operator=(value&&) noexcept = default;
 
        template <typename... ARGS>
        requires std::constructible_from<json, ARGS...>
        explicit(false) value(ARGS&&... args) noexcept : v(json(std::forward<ARGS>(args)...)) {}
 
        explicit(false) value(json&& j) noexcept : v(std::move(j)) {}
        explicit(false) value(json const* j) noexcept : v(std::move(j)) {}
        explicit(false) value(json* j) noexcept : v(std::move(j)) {}
 
        [[nodiscard]] bool is_lval() const noexcept { return v.index() == 1; }
        [[nodiscard]] bool is_rval() const noexcept { return v.index() == 0; }
        [[nodiscard]] bool is_ref() const noexcept { return v.index() == 2; }
 
        [[nodiscard]] json& lval() { return *std::get<json*>(v); }
 
        void ref() && = delete;
 
        [[nodiscard]] json const& ref() const&
        {
            switch (v.index())
            {
            case 0: return std::get<json>(v);
            case 1: return *std::get<json*>(v);
            case 2: return *std::get<json const*>(v);
            }
            return null_json;
        }
 
        [[nodiscard]] json const& forward() const&
        {
            return ref();
        }
 
        [[nodiscard]] json forward() &&
        {
            switch (v.index())
            {
            case 0: return std::move(std::get<json>(v));
            case 1: return *std::get<json*>(v);
            case 2: return *std::get<json const*>(v);
            }
            return null_json;
        }
 
        [[nodiscard]] explicit(false) operator json const& () const&
        {
            return ref();
        }
 
        [[nodiscard]] json const& operator*() const&
        {
            return ref();
        }
 
        [[nodiscard]] explicit(false) operator json () &&
        {
            return static_cast<value&&>(*this).forward();
        }
 
        [[nodiscard]] json operator*() &&
        {
            return static_cast<value&&>(*this).forward();
        }
 
        [[nodiscard]] json const* operator->() const& noexcept { return &ref(); }
    };

    template <bool DECADE_SYNTAX = false>
    struct environment
    {
        using self_type = environment<DECADE_SYNTAX>;
        static constexpr bool decade_syntax = DECADE_SYNTAX;
        static constexpr bool sexps_syntax = !DECADE_SYNTAX;
 
        using eval_func = std::function<value(self_type&, std::vector<value>)>;
 
        self_type* parent_env = nullptr; 
        std::map<std::string, eval_func, std::less<>> funcs;
        eval_func unknown_func_eval;
        std::function<value(self_type&, std::string_view)> unknown_var_eval;
        std::function<void(std::string_view)> error_handler;
        std::map<std::string, json, std::less<>> user_storage;
        void* user_data = nullptr;
        std::map<std::string, eval_func, std::less<>> prefix_macros; 
        std::function<bool(json const&)> truthiness_function;
 
        [[nodiscard]] self_type* get_root_env() const noexcept { return parent_env ? parent_env->get_root_env() : this; }
 
        [[nodiscard]] auto find_in_user_storage(std::string_view name)
        {
            return find_in_user_storage(*this, name);
        }
 
    private:
        static auto find_in_user_storage(auto& self, std::string_view name)
        {
            if (auto it = self.user_storage.find(name); it != self.user_storage.end())
                return std::pair{ &self, it };
            else
                return self.parent_env ? find_in_user_storage(*self.parent_env, name) : std::pair<decltype(&self), decltype(it)>{};
        }
    public:
 
        [[nodiscard]] value user_var(std::string_view name)
        {
            auto var = find_in_user_storage(name);
            if (var.first)
                return &var.second->second;
            return unknown_var_eval ? unknown_var_eval(*this, name) : value(null_json);
        }
 
        json& set_user_var(std::string_view name, value val, bool force_local = false)
        {
            auto* storage = &user_storage;
            if (!force_local)
            {
                auto [owning_store, it] = find_in_user_storage(name);
                if (owning_store)
                    storage = &owning_store->user_storage;
            }
            auto it = storage->find(name);
            if (it == storage->end())
                return storage->emplace(name, val.forward()).first->second;
            return it->second = val.forward();
        }
 
        [[nodiscard]] eval_func const* find_unknown_func_eval() const noexcept
        {
            if (unknown_func_eval)
                return &unknown_func_eval;
            if (parent_env)
                return parent_env->find_unknown_func_eval();
            return nullptr;
        }
 
        [[nodiscard]] eval_func const* find_func(std::string_view name) const
        {
            if (auto it = funcs.find(name); it != funcs.end())
                return &it->second;
            if (parent_env)
                return parent_env->find_func(name);
            return find_unknown_func_eval();
        }
 
        template <typename... ARGS>
        json report_error(std::string_view fmt, ARGS&&... args)
        {
            auto errstr = std::vformat(fmt, std::make_format_args(args...));
            if (error_handler)
            {
                error_handler(errstr);
                return null_json;
            }
            throw std::runtime_error(std::move(errstr));
        }
 
        struct e_scope_terminator {
            value result = json(json::value_t::discarded);
            virtual std::string_view type() const noexcept = 0;
            virtual ~e_scope_terminator() noexcept = default;
        };
 
        value eval_call(std::vector<value> args)
        {
            if (args.empty())
                return null_json;
 
            //const auto orig_args = args;
 
            std::string funcname;
            std::vector<value> arguments;
            if constexpr (decade_syntax)
            {
                const auto args_count = args.size();
                const bool infix = (args_count % 2) == 1;
 
                if (args_count == 1)
                {
                    funcname = *args[0];
                    arguments = std::move(args);
                }
                else
                {
                    arguments.push_back({}); 
                    if (infix)
                    {
                        arguments.push_back(std::move(args[0]));
                        funcname += ':';
                    }

                    std::string last_function_identifier;
                    bool argument_variadic = false;
                    for (size_t i = infix; i < args_count; i += 2)
                    {
                        auto& function_identifier = args[i];
                        if (function_identifier->is_string() && !std::string_view{*function_identifier}.empty())
                        {
                            if (last_function_identifier == std::string_view{ *function_identifier })
                            {
                                if (!argument_variadic)
                                {
                                    funcname.back() = '*';
                                    funcname += ':';
                                    argument_variadic = true;
                                }
                            }
                            else
                            {
                                argument_variadic = false;
                                funcname += *function_identifier;
                                funcname += ':';
                                last_function_identifier = *function_identifier;
                            }
                            arguments.push_back(std::move(args[i + 1]));
                        }
                        else
                            return report_error("expected function name part, got: {}", function_identifier->dump());
                    }
 
                    arguments[0] = funcname;
                }
            }
            else 
            {
                auto& func = *args[0];
                if (func.is_string())
                    funcname = func.get_ref<json::string_t const&>();
                else if (func.is_array())
                {
                    auto eres = eval_args(func.get_ref<json::array_t const&>());
                    if (eres.is_string())
                        funcname = eres.template get_ref<json::string_t const&>();
                }
                if (funcname.empty())
                    return report_error("first element of eval array must eval to a string func name, got: {}", func.dump());
            }
 
            if (eval_func const* func = find_func(funcname))
                return (*func)(*this, std::move(arguments));
            return report_error("func with name '{}' not found", funcname);
        }
 
        template <typename V>
        value eval(V&& val)
        {
            if constexpr (std::same_as<V, value const&>)
            {
                return eval(value{ val });
            }
            else if constexpr (std::same_as<std::remove_cvref_t<V>, json>)
            {
                return eval(value(std::forward<V>(val)));
            }
            else if constexpr (std::same_as<std::remove_cvref_t<V>, value>)
            {
                if (val->is_string())
                {
                    if (auto str = std::string_view{ *val }; !str.empty())
                    {
                        for (auto& [prefix, macro] : prefix_macros)
                        {
                            if (str.starts_with(prefix))
                                return eval(macro(*this, { std::move(val) }));
                        }
                    }
                }
 
                if (!val->is_array())
                    return std::move(val);
 
                std::vector<value> args;
                switch (val.v.index())
                {
                case 0:
                {
                    json::array_t arr = std::move(std::get<json>(val.v).template get_ref<json::array_t&>());
                    for (auto& a : arr)
                        args.push_back(std::move(a));
                    break;
                }
                case 1:
                {
                    json::array_t& arr = std::get<json*>(val.v)->template get_ref<json::array_t&>();
                    for (auto& a : arr)
                        args.push_back(&a);
                    break;
                }
                case 2:
                {
                    json::array_t const& arr = std::get<json const*>(val.v)->template get_ref<json::array_t const&>();
                    for (auto const& a : arr)
                        args.push_back(&a);
                    break;
                }
                }
 
                return eval_call(std::move(args));
            }
        }
 
        template <typename T>
        json safe_eval(T&& value)
        {
            try
            {
                auto result = eval(value);
                return result.forward();
            }
            catch (e_scope_terminator const& e)
            {
                return report_error("'{}' not in loop", e.type());
            }
        }
 
        [[nodiscard]] inline bool is_true(json const& val)
        {
            switch (val.type())
            {
            case json::value_t::boolean: return bool(val);
            case json::value_t::null: return false;
            default: return truthiness_function ? truthiness_function(val) : true;
            }
        }
 
        [[nodiscard]] inline bool is_true(value const& val)
        {
            return is_true(*val);
        }
 
        static void assert_args(std::span<value const> args, size_t arg_count)
        {
            if (args.size() != arg_count + 1)
                throw std::runtime_error(std::format("function {} requires exactly {} arguments, {} given", args[0]->dump(), arg_count, args.size() - 1));
        }
 
        static void assert_args(std::span<value const> args, size_t min_args, size_t max_args)
        {
            if (args.size() < min_args + 1 && args.size() >= max_args + 1)
                throw std::runtime_error(std::format("function {} requires between {} and {} arguments, {} given", args[0]->dump(), min_args, max_args, args.size() - 1));
        }
 
        static void assert_min_args(std::span<value const> args, size_t arg_count)
        {
            if (args.size() < arg_count + 1)
                throw std::runtime_error(std::format("function {} requires at least {} arguments, {} given", args[0]->dump(), arg_count, args.size() - 1));
        }
 
        static auto assert_arg(std::span<value const> args, size_t arg_num, json::value_t type = json::value_t::discarded)
        {
            if (arg_num >= args.size())
                throw std::runtime_error(std::format("function {} requires {} arguments, {} given", args[0]->dump(), arg_num, args.size() - 1));
 
            if (type != json::value_t::discarded && args[arg_num]->type() != type)
            {
                throw std::runtime_error(std::format("argument #{} to function {} must be of type {}, {} given",
                    arg_num, args[0]->dump(), formats::json::type_name(type), formats::json::type_name(args[arg_num]->type())));
            }
 
            return args[arg_num]->type();
        }
 
        template <std::same_as<nlohmann::json::value_t>... T>
        static void assert_args(std::vector<value> args, T... arg_types)
        {
            static constexpr size_t arg_count = sizeof...(T);
            assert_args(args, arg_count);
 
            const auto types = std::array{ arg_types... };
            for (size_t i = 0; i < types.size(); ++i)
            {
                if (types[i] != json::value_t::discarded)
                    assert_arg(args, i + 1, types[i]);
            }
        }
 
        value eval_arg(std::vector<value>& args, size_t n, json::value_t type = json::value_t::discarded)
        {
            assert_arg(args, n, type);
            return eval(std::move(args[n]));
        }
 
        void eval_args(std::vector<value>& args, size_t n)
        {
            assert_args(args, n);
            for (auto& arg : std::span{ args }.subspan(1))
                arg = eval(std::move(arg));
        }
 
        void eval_args(std::vector<value>& args)
        {
            eval_args(args, args.size() - 1);
        }
 
        template <typename LIB_TYPE>
        void import_lib()
        {
            LIB_TYPE::import_to(*this);
        }
 
        template <template<bool> typename LIB_TYPE>
        void import_lib()
        {
            LIB_TYPE<decade_syntax>::import_to(*this);
        }
    };

}