Header File lex/token_spec.hpp

The file token_spec.hpp contains the token specification and base tokens.

namespace lex
{
    // token specification
    template <class ... Tokens>
    struct token_spec {};
     
    struct error_token {}; 
    struct eof_token {};
    
    // traits
    template <typename T>
    struct is_token;
}

Token Specification

The tokens in a grammar are specified by creating a class that inherits from lex::token_spec passing it all the token types.

More details can be found in the tutorial.

The special token types lex::error_token, representing an invalid character (sequence), and lex::eof_token, representing the end of the input, is always included.

Traits

The traits all derive from either std::true_type or std::false_type, depending on the result of the condition.

is_token<T>: whether or not T is a token type.