trival: new class for tri-valued logic

* spot/misc/trival.hh: New file.
* spot/misc/Makefile.am: Add it.
* python/spot_impl.i: Add Python bindings.
* tests/core/trival.cc, tests/core/trival.test,
tests/python/trival.py: New files, testing it.
* tests/Makefile.am: Add them.

tests/core/trival.cc

@@ -0,0 +1,50 @@
+// -*- coding: utf-8 -*-
+// Copyright (C) 2016 Laboratoire de Recherche et Developpement de
+// l'Epita (LRDE).
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot 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 3 of the License, or
+// (at your option) any later version.
+//
+// Spot is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+// License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#undef NDEBUG
+#include <spot/misc/trival.hh>
+#include <cassert>
+
+int main()
+{
+  spot::trival v1;
+  spot::trival v2(false);
+  spot::trival v3(true);
+  spot::trival v4 = spot::trival::maybe();
+  assert(v1 != v2);
+  assert(v1 != v3);
+  assert(v2 != v3);
+  assert(v4 != v2);
+  assert(v4 != v3);
+  assert(v2 == false);
+  assert(true == v3);
+  assert(v4 == spot::trival::maybe());
+  assert(v3);
+  assert(!v2);
+  assert(!(bool)!v1);
+  assert(!(bool)v1);
+  assert(!(bool)!v3);
+
+  for (auto u : {v2, v1, v3})
+    for (auto v : {v2, v1, v3})
+      std::cout << u << " && " << v << " == " << (u && v) << '\n';
+  for (auto u : {v2, v1, v3})
+    for (auto v : {v2, v1, v3})
+      std::cout << u << " || " << v << " == " << (u || v) << '\n';
+}