datalog_term.hpp

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#pragma once
 
#include <cstddef>
#include <functional>
#include <string>
 
namespace pulsatrix::datalog {
 
enum class TermKind { Constant, Variable };
 
class Term {
public:
    static Term make_constant(std::string value) { return Term(TermKind::Constant, std::move(value)); }
 
    static Term make_variable(std::string name) { return Term(TermKind::Variable, std::move(name)); }
 
    [[nodiscard]] TermKind kind() const { return kind_; }
 
    [[nodiscard]] bool is_constant() const { return kind_ == TermKind::Constant; }
 
    [[nodiscard]] bool is_variable() const { return kind_ == TermKind::Variable; }
 
    [[nodiscard]] const std::string& value() const { return value_; }
 
    [[nodiscard]] bool operator==(const Term& other) const {
        return kind_ == other.kind_ && value_ == other.value_;
    }
    [[nodiscard]] bool operator!=(const Term& other) const { return !(*this == other); }
 
private:
    Term(TermKind kind, std::string value) : kind_(kind), value_(std::move(value)) {}
 
    TermKind kind_;
    std::string value_;
};
 
struct TermHash {
    [[nodiscard]] std::size_t operator()(const Term& term) const {
        return std::hash<std::string>{}(term.value()) ^ (static_cast<std::size_t>(term.kind()) << 1);
    }
};
 
}  // namespace pulsatrix::datalog