Error while making on Ubuntu 16.04

[guicho271828]

[guicho VAL]$ LANG=C bison --version
bison (GNU Bison) 3.0.4
Written by Robert Corbett and Richard Stallman.

Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
[guicho VAL]$ LANG=C c++ --version
c++ (Ubuntu 5.4.0-6ubuntu1~16.04.1) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[guicho VAL]$ uname -a 
Linux guicho-desktop 4.4.0-31-generic #50-Ubuntu SMP Wed Jul 13 00:07:12 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
[guicho VAL]$ LANG=C make
g++ -g   -o validate src/pddl+.o src/ptree.o src/Action.o src/Proposition.o src/FuncExp.o src/typecheck.o src/main.o src/Validator.o src/RepairAdvice.o src/LaTeXSupport.o src/State.o src/Plan.o src/Ownership.o src/Environment.o src/Polynomial.o src/DebugWriteController.o src/Utils.o src/TrajectoryConstraints.o src/RobustAnalyse.o src/random.o src/Events.o src/PrettyPrinter.o 
src/pddl+.o: In function `yyparse()':
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:269: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:274: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:317: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:340: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:378: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:514: undefined reference to `VAL::var_symbol_table_stack::symbol_get(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:635: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:690: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:704: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:1150: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:1159: undefined reference to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
src/pddl+.o:/home/guicho/repos/c-or-cpp/VAL/src/pddl+.yacc:1168: more undefined references to `VAL::log_error(VAL::error_severity, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)' follow
collect2: error: ld returned 1 exit status
Makefile:80: recipe for target 'validate' failed
make: *** [validate] Error 1

[guicho271828]

fixed in #25