krat_exp_parser.hxx

// krat_exp_parser.hxx: this file is part of the Vaucanson project.
//
// Vaucanson, a generic library for finite state machines.
//
// Copyright (C) 2001, 2002, 2003, 2004 The Vaucanson Group.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// The complete GNU General Public Licence Notice can be found as the
// `COPYING' file in the root directory.
//
// The Vaucanson Group consists of people listed in the `AUTHORS' file.
//
#ifndef VCSN_ALGEBRA_IMPLEMENTATION_SERIES_KRAT_EXP_PARSER_HXX
# define VCSN_ALGEBRA_IMPLEMENTATION_SERIES_KRAT_EXP_PARSER_HXX

# include <vaucanson/algebra/implementation/series/krat_exp_parser.hh>

# include <vaucanson/algebra/concept/monoid_base.hh>
# include <vaucanson/tools/usual_escaped_characters.hh>

# include <list>
# include <set>

namespace vcsn {

  namespace algebra {


    namespace krat_exp_lexing {

      enum token_e
        {
          lparen,
          rparen,
          space,
          plus,
          e_star,
          dot,
          zero,
          one,
          a_word,
          a_weight,
          eof
        };

    } // krat_exp_lexing

    using namespace krat_exp_lexing;

    template <class MonoidValue, class SemiringEltValue>
    class KRatExpToken
    {
    public:
      struct token
      {
        token(const token_e& tok_type) :
          type(tok_type)
        {}

        token(const token_e& tok_type, const MonoidValue& word)
        {
          m = word;
          type = tok_type;
        }

        token(const token_e& tok_type, const SemiringEltValue& weight)
        {
          w = weight;
          type = tok_type;
        }

        std::string to_string() const
        {
          switch (type)
            {
            case a_word                 : return "word";
            case a_weight               : return "weight";
            case lparen                 : return "(";
            case rparen                 : return ")";
            case one                    : return "one";
            case zero                   : return "zero";
            case krat_exp_lexing::dot   : return ".";
            case e_star                 : return "*";
            case krat_exp_lexing::plus  : return "+";
            case space                  : return " ";
            case eof                    : return "EOF";
            }
          return "";
        }

        token_e type;
        MonoidValue m;
        SemiringEltValue w;
      };

      KRatExpToken(const token_e& tok)
      {
        tok_.push_back(tok);
      }

      KRatExpToken()
      {
      }

      std::string to_string() const
      {
        if (tok_.size() == 0)
          return "no token";
        else if (tok_.size() == 1)
          return tok_.front().to_string();
        else
          {
            std::string s("schrod(");
            typename std::list<token>::const_iterator i = tok_.begin();
            while (i != tok_.end())
              s += i->to_string() + (++i != tok_.end() ? " ": "");
            s += ")";
            return s;
          }
      }

      bool is_just_a(const token_e tok)
      {
        return ((tok_.size() == 1) && (tok_.front().type == tok));
      }

      bool is_defined()
      {
        return (tok_.size() > 0);
      }

      bool is_schrod()
      {
        return (tok_.size() > 1);
      }

      bool is_a(const token_e tok)
      {
        for (typename std::list<token>::const_iterator i = tok_.begin();
             i != tok_.end();
             ++i)
          if (i->type == tok)
            return true;
        return false;
      }

      MonoidValue as_word()
      {
        for (typename std::list<token>::const_iterator i = tok_.begin();
             i != tok_.end();
             ++i)
          if (i->type == a_word)
            return i->m;
        unreachable("internal error in krat_exp parser");
        return MonoidValue();
      }

      SemiringEltValue as_weight()
      {
        for (typename std::list<token>::const_iterator i = tok_.begin();
             i != tok_.end();
             ++i)
          if (i->type == a_weight)
            return i->w;
        unreachable("internal error in krat_exp parser.");
        return SemiringEltValue();
      }

      KRatExpToken& operator=(const token_e tok)
      {
        tok_.push_back(token(tok));
        return *this;
      }

      KRatExpToken& operator=(const MonoidValue& word_value)
      {
        tok_.push_back(token(a_word, word_value));
        return *this;
      }

      KRatExpToken& operator=(const SemiringEltValue& weight_value)
      {
        tok_.push_back(token(a_weight, weight_value));
        return *this;
      }

      void reset()
      {
        tok_.clear();
      }

    private:
      std::list<token> tok_;
    };

    template <class S, class T>
    struct Lexer
    {
      typedef KRatExpToken
      <
        typename Element<S, T>::monoid_elt_value_t,
        typename Element<S, T>::semiring_elt_value_t
      >                                               krat_exp_token_t;
      typedef std::list<krat_exp_token_t>             token_stream_t;

      Lexer(bool trace = false) :
        tokens_ (),
        trace_ (trace),
        error_msg_ ("No error."),
        error_ (false)
      {
      }

      void
      lex_error(const std::string& msg = "Lex error.")
      {
        error_ = true;
        error_msg_ = msg;
      }

      void
      lex(const std::string& in, const Element<S, T>& e)
      {
        typedef typename Element<S, T>::monoid_elt_t       monoid_elt_t;
        typedef typename Element<S, T>::monoid_elt_value_t monoid_elt_value_t;
        typedef typename Element<S, T>::semiring_elt_t     semiring_elt_t;
        typedef std::string::const_iterator                iterator_t;

        iterator_t i = in.begin();
        std::set<char> escaped = tools::usual_escaped_characters();
        int len = 0;

        while (!error_ & (i != in.end()))
          {
            len = 0;
            krat_exp_token_t tok;
            switch (*i)
              {
                // operator case.
              case '(' : tok = lparen;                  len = 1; break;
              case ')' : tok = rparen;                  len = 1; break;
              case '+' : tok = krat_exp_lexing::plus;   len = 1; break;
              case '*' : tok = e_star;                  len = 1; break;
              case '.' : tok = krat_exp_lexing::dot;    len = 1; break;
              case ' ' : tok = space;                   len = 1; break;
              case '0' : tok = zero;                    len = 1; break;
              case '1' : tok = one;                     len = 1; break;
              }
            // try word parser.
            iterator_t mli = i;
            monoid_elt_t w (e.structure().monoid());
            if (parse_word(w, in, mli, escaped))
              {
                if (mli - i > 1)
                  tok.reset();
                tok = w.value();
                len = mli - i;
              }
            // try weight lexer.
            iterator_t wli = i;
            semiring_elt_t ww (e.structure().semiring());
            if (parse_weight(ww, in, wli))
              {
                if (wli - i > len)
                  tok.reset();
                if (wli - i >= len)
                  {
                    tok = ww.value();
                    len = wli - i;
                  }
              }
            if (len == 0)
              lex_error(std::string("Invalid token '") + *i + "'.");
            else
              tokens_.push_back(tok);
            i += len;
          }
      }

      bool
      error() const
      {
        return error_;
      }

      const std::string&
      error_msg() const
      {
        return error_msg_;
      }

      krat_exp_token_t first() const
      {
        return (tokens_.size() > 0) ? tokens_.front() :
          krat_exp_token_t (eof);
      }

      krat_exp_token_t second() const
      {
        return (tokens_.size() >= 2) ?
          *++tokens_.begin() : krat_exp_token_t (eof);
      }

      void eat()
      {
        if (tokens_.size() > 0)
          {
            if (trace_)
              std::cerr << "LEXER: eating '" << tokens_.front().to_string()
                        << "'." << std::endl;
            tokens_.pop_front();
          }
      }

      void set_trace(bool trace)
      {
        trace_ = trace;
      }

    protected:
      token_stream_t tokens_;
      bool trace_;
      std::string error_msg_;
      bool error_;
    };

    template <class S, class T>
    struct Parser
    {
      typedef KRatExpToken
      <
        typename Element<S, T>::monoid_elt_value_t,
        typename Element<S, T>::semiring_elt_value_t
      >                                               krat_exp_token_t;
      typedef typename Element<S, T>::monoid_elt_t    monoid_elt_t;
      typedef typename Element<S, T>::monoid_elt_value_t  monoid_elt_value_t;
      typedef typename monoid_elt_t::set_t            monoid_t;
      typedef typename Element<S, T>::semiring_elt_t          semiring_elt_t;
      typedef typename semiring_elt_t::set_t                  semiring_t;
      typedef typename Element<S, T>::semiring_elt_value_t  semiring_elt_value_t;
      typedef std::list<krat_exp_token_t>             token_stream_t;

      Parser(Lexer<S, T>& lexer, bool trace = false) :
        lexer_          (lexer),
        trace_          (trace),
        error_          (lexer.error()),
        error_msg_      (lexer.error_msg())
      {
      }

      void parse(Element<S, T>& exp)
      {
        if (!error_)
          {
            trace("*** START ***");
            try
              {
                parse_exp(exp);
                accept(eof);
              }
            catch (const std::string& s)
              {
                error_ = true;
                error_msg_ = s;
              }
            trace("*** END ***");
          }
      }

      bool error() const
      {
        return error_;
      }

      const std::string& error_msg() const
      {
        return error_msg_;
      }

      void set_trace(bool trace)
      {
        trace_ = trace;
      }

    protected:


      void
      trace(const std::string& msg)
      {
        if (trace_)
          std::cerr << "PARSER: " << msg << '.' << std::endl;
      }

      template <class Misc>
      void
      trace(const std::string& msg, const Misc& v)
      {
        if (trace_)
          std::cerr << "PARSER: " << msg << " (" << v << ")." << std::endl;
      }

      void parse_error(const std::string& msg = "parse_error.")
        throw (const std::string&)
      {
        trace("Stop on error.", msg);
        throw msg;
      }

      void accept(token_e tok)
      {
        krat_exp_token_t                        get_token = lexer_.first();
        typename krat_exp_token_t::token        expected (tok);

        trace("accept", expected.to_string());
        if (!get_token.is_a(tok))
          parse_error("waiting for a '" + expected.to_string() +
                      "' get a '" + get_token.to_string() + "'.");
        else
          lexer_.eat();
      }

      void parse_exp(Element<S, T>& exp)
      {
        trace("parse_exp: Start");
        parse_term (exp);
        while (lexer_.first().is_a(krat_exp_lexing::plus))
          {
            accept(krat_exp_lexing::plus);
            Element<S, T> rhs (exp.structure());
            parse_term(rhs);
            exp = exp + rhs;
          }
        trace("parse_exp: End",  exp);
      }

      void parse_term(Element<S, T>& exp)
      {
        trace("parse_term: Start");
        parse_right_weighted (exp);
        while (lexer_.first().is_a(krat_exp_lexing::dot)        ||
               lexer_.first().is_a(a_weight)                    ||
               lexer_.first().is_a(lparen)                      ||
               lexer_.first().is_a(one)                         ||
               lexer_.first().is_a(zero)                        ||
               lexer_.first().is_a(a_word))
          {
            if (lexer_.first().is_a(krat_exp_lexing::dot))
              accept(krat_exp_lexing::dot);
            Element<S, T> rhs (exp.structure());
            parse_right_weighted(rhs);
            exp = exp * rhs;
          }
        trace("parse_term: End",  exp);
      }

      void parse_right_weighted(Element<S, T>& exp)
      {
        trace("parse_right_weighted: Start");
        parse_left_weighted(exp);
        while (lexer_.first().is_a(space))
          {
            accept(space);
            krat_exp_token_t tok = lexer_.first();
            accept(a_weight);
            exp = exp * semiring_elt_t (exp.structure().semiring(), tok.as_weight());
          }
        trace("parse_right_weighted: End", exp);
      }

      void parse_left_weighted(Element<S, T>& exp)
      {
        trace("parse_left_weighted: Start");
        // a 2-lookahead will be sufficient to disambiguate.
        if (lexer_.first().is_a(a_weight) &&
            (!lexer_.first().is_schrod() || lexer_.second().is_a(space)))
          {
            // token must be a weight, but may be a monoid '1' or '0'.
            // i.e. in "1 2" or "0 2".
            // token may even be a word!
            // i.e. in '2 3' when 2 is in the alphabet
            semiring_elt_t w (exp.structure().semiring(), lexer_.first().as_weight());
            bool just_a_weight = true;
            Element<S, T> m (exp.structure());
            if (lexer_.first().is_a(zero))
              {
                just_a_weight = false;
                m = zero_as<T>::of(exp.structure());
              }
            else if (lexer_.first().is_a(one))
              {
                just_a_weight = false;
                m = identity_as<T>::of(exp.structure());
              }
            else if (lexer_.first().is_a(a_word))
              {
                just_a_weight = false;
                m = Element<S, T> (exp.structure(), lexer_.first().as_word());
              }
            accept(a_weight);
            accept(space);
            if (just_a_weight ||
                !lexer_.first().is_a(a_weight) ||
                lexer_.second().is_a(space))
              {
                // Then it could be any weighted.
                Element<S, T> rhs (exp.structure());
                parse_left_weighted(rhs);
                exp = w * rhs;
              }
            else
              {
                // Arg ! First was not a weight, but a monoid value !
                w = lexer_.first().as_weight();
                accept(a_weight);
                exp = m * w;
              }
          }
        else
          /* !lexer_.first().is_a(a_weight)  ||
             (lexer_.first.is_schrod() && !lexer_.second().is_a(space)) */
          parse_stared(exp);
        trace("parse_left_weighted: End",  exp);
      }

      void parse_stared(Element<S, T>& exp)
      {
        trace("parse_stared: Start");
        parse_factor(exp);
        while (lexer_.first().is_a(e_star))
          {
            accept(e_star);
            exp.star();
          }
        trace("parse_stared: End",  exp);
      }

      void parse_factor(Element<S, T>& exp)
      {
        trace("parse_factor: Start");
        if (lexer_.first().is_a(one))
          {
            accept(one);
            exp = identity_as<T>::of(exp.structure());
          }
        else if (lexer_.first().is_a(zero))
          {
            accept(zero);
            exp = zero_as<T>::of(exp.structure());
          }
        else if (lexer_.first().is_a(a_word))
          {
            exp = monoid_elt_t (exp.structure().monoid(), lexer_.first().as_word());
            accept(a_word);
          }
        else if (lexer_.first().is_a(lparen))
          {
            accept(lparen);
            parse_exp(exp);
            accept(rparen);
          }
        else
          parse_error("waiting for a factor get a " +
                      lexer_.first().to_string());
        trace("parse_factor: End",  exp);
      }

      Lexer<S, T>&      lexer_;
      bool              trace_;
      bool              error_;
      std::string       error_msg_;
    };

    template <class S, class T>
    std::pair<bool, std::string>
    parse(const std::string& from,
          Element<S, T>& exp,
          bool lex_trace,
          bool parse_trace)
    {
      Lexer<S, T> lexer(lex_trace);
      lexer.lex(from, exp);
      Parser<S, T> parser(lexer, parse_trace);
      parser.parse(exp);
      return std::make_pair(parser.error(), parser.error_msg());
    }

  } // algebra

} // vcsn

#endif // ! VCSN_ALGEBRA_IMPLEMENTATION_SERIES_KRAT_EXP_PARSER_HXX

---