lb.Lexing.lex_start_p <- {lex_start_p with Lexing.pos_fname = filename};
lb.Lexing.lex_curr_p <- {lex_curr_p with Lexing.pos_fname = filename}
lb.Lexing.lex_start_p <- {lex_start_p with Lexing.pos_fname = filename};
lb.Lexing.lex_curr_p <- {lex_curr_p with Lexing.pos_fname = filename}