revamp the formula hierarchy (montro-patch)

Flatten the formula ltl::formula hiearchy into a single ltl::vnode that
has an enumerator to distinguish the types of node, and a common
interface to access children, update reference counts, etc.  The
ltl::formula class is now a thin wrapper around an ltl::vnode pointer to
keep track of reference counts automatically.  Visitor are not used
anymore; we now have map() and traversor() methods that are more
concise.

This basically fixes #43, but should be followed by some fine tuning
that should now be localized to the formula.hh and formula.cc files.

Some statistics about this patch.  I started working on it on Sep 9, had
a first compiling version two weeks later on Sep 22, and it then took 5
days to fixes the ~70 distincts bugs that were introduced during the
conversion.  About 13200 lines were modified, and one third of those
were removed.

* src/ltlast/formula.cc, src/ltlast/formula.hh: Complete rewrite,
including what was in separate nearby files.
* src/ltlast/allnodes.hh, src/ltlast/atomic_prop.cc,
src/ltlast/atomic_prop.hh, src/ltlast/binop.cc, src/ltlast/binop.hh,
src/ltlast/bunop.cc, src/ltlast/bunop.hh, src/ltlast/constant.cc,
src/ltlast/constant.hh, src/ltlast/multop.cc, src/ltlast/multop.hh,
src/ltlast/unop.cc, src/ltlast/unop.hh, src/ltlvisit/dump.cc,
src/ltlvisit/dump.hh, src/ltlast/predecl.hh: Delete these files.  Their
feature have been merged in formula.hh and formula.cc.
* src/ltlast/visitor.hh, src/ltlvisit/clone.cc, src/ltlvisit/clone.hh,
src/ltlvisit/dump.hh, src/ltlvisit/postfix.cc, src/ltlvisit/postfix.hh:
Delete these files, as we do not use visitors anymore.
* bench/stutter/stutter_invariance_formulas.cc,
bench/stutter/stutter_invariance_randomgraph.cc, doc/org/tut01.org,
doc/org/tut02.org, doc/org/tut10.org, doc/org/tut22.org,
iface/ltsmin/ltsmin.cc, iface/ltsmin/ltsmin.hh,
iface/ltsmin/modelcheck.cc, src/bin/autfilt.cc,
src/bin/common_aoutput.cc, src/bin/common_aoutput.hh,
src/bin/common_finput.cc, src/bin/common_finput.hh,
src/bin/common_output.cc, src/bin/common_output.hh,
src/bin/common_trans.cc, src/bin/common_trans.hh, src/bin/dstar2tgba.cc,
src/bin/genltl.cc, src/bin/ltl2tgba.cc, src/bin/ltl2tgta.cc,
src/bin/ltlcross.cc, src/bin/ltldo.cc, src/bin/ltlfilt.cc,
src/bin/ltlgrind.cc, src/bin/randaut.cc, src/bin/randltl.cc,
src/kripke/kripkeexplicit.cc, src/kripke/kripkeexplicit.hh,
src/kripkeparse/kripkeparse.yy, src/ltlast/Makefile.am,
src/ltlenv/declenv.cc, src/ltlenv/declenv.hh, src/ltlenv/defaultenv.cc,
src/ltlenv/defaultenv.hh, src/ltlenv/environment.hh,
src/ltlparse/ltlparse.yy, src/ltlparse/public.hh,
src/ltlvisit/Makefile.am, src/ltlvisit/apcollect.cc,
src/ltlvisit/apcollect.hh, src/ltlvisit/contain.cc,
src/ltlvisit/contain.hh, src/ltlvisit/dot.cc, src/ltlvisit/dot.hh,
src/ltlvisit/exclusive.cc, src/ltlvisit/exclusive.hh,
src/ltlvisit/length.cc, src/ltlvisit/length.hh, src/ltlvisit/mark.cc,
src/ltlvisit/mark.hh, src/ltlvisit/mutation.cc,
src/ltlvisit/mutation.hh, src/ltlvisit/nenoform.cc,
src/ltlvisit/nenoform.hh, src/ltlvisit/print.cc, src/ltlvisit/print.hh,
src/ltlvisit/randomltl.cc, src/ltlvisit/randomltl.hh,
src/ltlvisit/relabel.cc, src/ltlvisit/relabel.hh,
src/ltlvisit/remove_x.cc, src/ltlvisit/remove_x.hh,
src/ltlvisit/simpfg.cc, src/ltlvisit/simpfg.hh,
src/ltlvisit/simplify.cc, src/ltlvisit/simplify.hh, src/ltlvisit/snf.cc,
src/ltlvisit/snf.hh, src/ltlvisit/unabbrev.cc, src/ltlvisit/unabbrev.hh,
src/parseaut/parseaut.yy, src/ta/taexplicit.cc, src/ta/tgtaexplicit.cc,
src/taalgos/minimize.cc, src/taalgos/tgba2ta.cc, src/tests/bare.test,
src/tests/checkpsl.cc, src/tests/checkta.cc,
src/tests/complementation.cc, src/tests/consterm.cc,
src/tests/emptchk.cc, src/tests/equalsf.cc, src/tests/ikwiad.cc,
src/tests/isop.test, src/tests/kind.cc, src/tests/length.cc,
src/tests/ltldo.test, src/tests/ltlfilt.test, src/tests/ltlgrind.test,
src/tests/ltlprod.cc, src/tests/ltlrel.cc,
src/tests/parse_print_test.cc, src/tests/parseaut.test,
src/tests/parseerr.test, src/tests/randtgba.cc, src/tests/readltl.cc,
src/tests/reduc.cc, src/tests/syntimpl.cc, src/tests/taatgba.cc,
src/tests/tostring.cc, src/tests/twagraph.cc, src/tests/utf8.test,
src/twa/acc.cc, src/twa/bdddict.cc, src/twa/bdddict.hh,
src/twa/bddprint.cc, src/twa/formula2bdd.cc, src/twa/formula2bdd.hh,
src/twa/taatgba.cc, src/twa/taatgba.hh, src/twa/twa.cc, src/twa/twa.hh
src/twa/twagraph.cc, src/twa/twagraph.hh, src/twa/twasafracomplement.cc,
src/twaalgos/compsusp.cc, src/twaalgos/compsusp.hh,
src/twaalgos/dtgbasat.cc, src/twaalgos/hoa.cc, src/twaalgos/lbtt.cc,
src/twaalgos/ltl2taa.cc, src/twaalgos/ltl2taa.hh,
src/twaalgos/ltl2tgba_fm.cc, src/twaalgos/ltl2tgba_fm.hh,
src/twaalgos/minimize.cc, src/twaalgos/minimize.hh,
src/twaalgos/neverclaim.cc, src/twaalgos/postproc.cc,
src/twaalgos/postproc.hh, src/twaalgos/powerset.cc,
src/twaalgos/powerset.hh, src/twaalgos/randomgraph.cc,
src/twaalgos/remprop.cc, src/twaalgos/remprop.hh, src/twaalgos/stats.cc,
src/twaalgos/stats.hh, src/twaalgos/stutter.cc, src/twaalgos/stutter.hh,
src/twaalgos/translate.cc, src/twaalgos/translate.hh,
wrap/python/ajax/spotcgi.in, wrap/python/spot.py,
wrap/python/spot_impl.i, wrap/python/Makefile.am,
wrap/python/tests/automata-io.ipynb, wrap/python/tests/formulas.ipynb,
wrap/python/tests/ltl2tgba.py, wrap/python/tests/ltlparse.py,
wrap/python/tests/ltlsimple.py, wrap/python/tests/randltl.ipynb: Adjust
to use the new interface.
* src/sanity/style.test: Accept more C++11 patterns.
* NEWS: Mention the change.

src/ltlvisit/exclusive.cc

@@ -18,10 +18,6 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include "exclusive.hh"
-#include "ltlenv/defaultenv.hh"
-#include "ltlast/multop.hh"
-#include "ltlast/unop.hh"
-#include "ltlast/constant.hh"
 #include "twaalgos/mask.hh"
 #include "misc/casts.hh"
 #include "misc/minato.hh"
@@ -29,20 +25,12 @@
 
 namespace spot
 {
-  exclusive_ap::~exclusive_ap()
-  {
-    for (auto& g: groups)
-      for (auto ap: g)
-	ap->destroy();
-  }
-
   namespace
   {
-    static const std::vector<const spot::ltl::atomic_prop*>
+    static const std::vector<ltl::formula>
     split_aps(const char* arg)
     {
-      auto& env = spot::ltl::default_environment::instance();
-      std::vector<const spot::ltl::atomic_prop*> group;
+      std::vector<ltl::formula> group;
       auto start = arg;
       while (*start)
 	{
@@ -73,8 +61,7 @@ namespace spot
 		  throw std::invalid_argument(s);
 		}
 	      std::string ap(start, end - start);
-	      auto* t = env.require(ap);
-	      group.push_back(down_cast<const spot::ltl::atomic_prop*>(t));
+	      group.emplace_back(ltl::formula::ap(ap));
 	      do
 		++end;
 	      while (*end == ' ' || *end == '\t');
@@ -99,8 +86,7 @@ namespace spot
 	      while (rend > start && (rend[-1] == ' ' || rend[-1] == '\t'))
 		--rend;
 	      std::string ap(start, rend - start);
-	      auto* t = env.require(ap);
-	      group.push_back(down_cast<const spot::ltl::atomic_prop*>(t));
+	      group.emplace_back(ltl::formula::ap(ap));
 	      if (*end == ',')
 		start = end + 1;
 	      else
@@ -116,29 +102,27 @@ namespace spot
     add_group(split_aps(ap_csv));
   }
 
-  void exclusive_ap::add_group(std::vector<const ltl::atomic_prop*> ap)
+  void exclusive_ap::add_group(std::vector<ltl::formula> ap)
   {
     groups.push_back(ap);
   }
 
   namespace
   {
-    const ltl::formula*
-    nand(const ltl::formula* lhs, const ltl::formula* rhs)
+    ltl::formula
+    nand(ltl::formula lhs, ltl::formula rhs)
     {
-      auto f = ltl::multop::instance(ltl::multop::And,
-				     lhs->clone(), rhs->clone());
-      return ltl::unop::instance(ltl::unop::Not, f);
+      return ltl::formula::Not(ltl::formula::And({lhs, rhs}));
     }
   }
 
-  const ltl::formula*
-  exclusive_ap::constrain(const ltl::formula* f) const
+  ltl::formula
+  exclusive_ap::constrain(ltl::formula f) const
   {
-    spot::ltl::atomic_prop_set* s = atomic_prop_collect(f);
+    auto* s = atomic_prop_collect(f);
 
-    std::vector<const ltl::atomic_prop*> group;
-    ltl::multop::vec* v = new ltl::multop::vec;
+    std::vector<ltl::formula> group;
+    std::vector<ltl::formula> v;
 
     for (auto& g: groups)
       {
@@ -151,14 +135,11 @@ namespace spot
 	unsigned s = group.size();
 	for (unsigned j = 0; j < s; ++j)
 	  for (unsigned k = j + 1; k < s; ++k)
-	    v->push_back(nand(group[j], group[k]));
+	    v.push_back(nand(group[j], group[k]));
       };
 
     delete s;
-
-    auto* c = ltl::unop::instance(ltl::unop::G,
-				  ltl::multop::instance(ltl::multop::And, v));
-    return ltl::multop::instance(ltl::multop::And, f->clone(), c);
+    return ltl::formula::And({f, ltl::formula::G(ltl::formula::And(v))});
   }
 
   twa_graph_ptr exclusive_ap::constrain(const_twa_graph_ptr aut,