Replace the constant_term visitor by a flag in the formulae.

* src/ltlast/formula.hh (formula::accepts_eword): New method.
(formula::is.accepting_eword): New flag.
* src/ltlast/formula.cc (print_formula_props): Display the new
property.
* src/ltlast/atomic_prop.cc, src/ltlast/automatop.cc,
src/ltlast/binop.cc, src/ltlast/bunop.cc, src/ltlast/constant.cc,
src/ltlast/multop.cc, src/ltlast/unop.cc: Update
is.accepting_eword as appropriate.
* src/ltltest/consterm.cc, src/tgbaalgos/ltl2tgba_fm.cc: Adjust to
use accepts_eword().
* src/ltlvisit/consterm.cc, src/ltlvisit/consterm.hh: Delete.
* src/ltlvisit/Makefile.am: Remove these files.

src/ltlast/atomic_prop.cc

@@ -45,6 +45,7 @@ namespace spot
       is.eventual = false;
       is.universal = false;
       is.not_marked = true;
+      is.accepting_eword = false;
     }
 
     atomic_prop::~atomic_prop()

src/ltlast/automatop.cc

@@ -41,6 +41,7 @@ namespace spot
       is.eventual = false;
       is.universal = false;
       is.not_marked = true;
+      is.accepting_eword = false;
 
       unsigned s = v->size();
       for (unsigned i = 0; i < s; ++i)

src/ltlast/binop.cc

@@ -56,6 +56,7 @@ namespace spot
 	case Equiv:
 	  is.sugar_free_boolean = false;
 	  is.in_nenoform = false;
+	  is.accepting_eword = false;
 	  break;
 	case EConcatMarked:
 	  is.not_marked = false;
@@ -65,6 +66,7 @@ namespace spot
 	  is.ltl_formula = false;
 	  is.boolean = false;
 	  is.eltl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	case U:
 	  // 1 U a = Fa
@@ -72,6 +74,7 @@ namespace spot
 	    is.eventual = 1;
 	  is.boolean = false;
 	  is.eltl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	case W:
 	  // a W 0 = Ga
@@ -79,6 +82,7 @@ namespace spot
 	    is.universal = 1;
 	  is.boolean = false;
 	  is.eltl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	case R:
 	  // 0 R a = Ga
@@ -86,6 +90,7 @@ namespace spot
 	    is.universal = 1;
 	  is.boolean = false;
 	  is.eltl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	case M:
 	  // a M 1 = Fa
@@ -93,6 +98,7 @@ namespace spot
 	    is.eventual = 1;
 	  is.boolean = false;
 	  is.eltl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	}
     }

src/ltlast/bunop.cc

@@ -35,16 +35,21 @@ namespace spot
     {
       props = child->get_props();
 
+      is.boolean = false;
+      is.ltl_formula = false;
+      is.eltl_formula = false;
+      is.eventual = false;
+      is.universal = false;
+
       switch (op_)
 	{
-	case Equal:
 	case Star:
+	  if (min_ == 0)
+	    is.accepting_eword = true;
+	  break;
+	case Equal:
 	case Goto:
-	  is.boolean = false;
-	  is.ltl_formula = false;
-	  is.eltl_formula = false;
-	  is.eventual = false;
-	  is.universal = false;
+	  is.accepting_eword = (min_ == 0);
 	  break;
 	}
     }

src/ltlast/constant.cc

@@ -51,6 +51,7 @@ namespace spot
 	  is.eventual = true;
 	  is.universal = true;
 	  is.not_marked = true;
+	  is.accepting_eword = false;
 	  break;
 	case constant::EmptyWord:
 	  is.boolean = false;
@@ -64,6 +65,7 @@ namespace spot
 	  is.eventual = false;
 	  is.universal = false;
 	  is.not_marked = true;
+	  is.accepting_eword = true;
 	  break;
 	}
     }

src/ltlast/formula.cc

@@ -86,6 +86,7 @@ namespace spot
       proprint(is_eventual, "e", "pure eventuality");
       proprint(is_universal, "u", "purely universal");
       proprint(is_marked, "+", "marked");
+      proprint(accepts_eword, "0", "accepts the empty word");
       return out;
     }
   }

src/ltlast/formula.hh

@@ -211,6 +211,12 @@ namespace spot
 	return !is.not_marked;
       }
 
+      /// Whether the formula accepts [*0].
+      bool accepts_eword() const
+      {
+	return is.accepting_eword;
+      }
+
       /// The properties as a field of bits.  For internal use.
       unsigned get_props() const
       {
@@ -252,7 +258,7 @@ namespace spot
 	// "the formula is".
 	bool boolean:1;		   // No temporal operators.
 	bool sugar_free_boolean:1; // Only AND, OR, and NOT operators.
-	bool in_nenoform:1;	   // Negative Normal Form
+	bool in_nenoform:1;	   // Negative Normal Form.
 	bool X_free:1;		   // No X operators.
 	bool sugar_free_ltl:1;	   // No F and G operators.
 	bool ltl_formula:1;	   // Only LTL operators.
@@ -260,7 +266,8 @@ namespace spot
 	bool psl_formula:1;	   // Only PSL operators.
 	bool eventual:1;	   // Purely eventual formula.
 	bool universal:1;	   // Purely universal formula.
-	bool not_marked:1;	   // No occurrence of EConcatMarked
+	bool not_marked:1;	   // No occurrence of EConcatMarked.
+	bool accepting_eword:1;	   // Accepts the empty word.
       };
       union
       {

src/ltlast/multop.cc

@@ -28,7 +28,6 @@
 #include "multop.hh"
 #include "constant.hh"
 #include "visitor.hh"
-#include "ltlvisit/consterm.hh"
 
 namespace spot
 {
@@ -40,10 +39,6 @@ namespace spot
       unsigned s = v->size();
       assert(s > 1);
 
-      props = (*v)[0]->get_props();
-      for (unsigned i = 1; i < s; ++i)
-	props &= (*v)[i]->get_props();
-
       switch (op)
 	{
 	case Concat:
@@ -53,15 +48,29 @@ namespace spot
 	  is.eltl_formula = false;
 	  is.eventual = false;
 	  is.universal = false;
-	  break;
+	  // fall through
 	case AndNLM:
 	  // The non-matching-length-And (&) can only appear in the
 	  // rational parts of PSL formula.  We don't remove the
 	  // Boolean flag, because applied to atomic propositions a&b
 	  // has the same effect as a&&b.
 	case And:
-	case Or:
+	  props = (*v)[0]->get_props();
+	  for (unsigned i = 1; i < s; ++i)
+	    props &= (*v)[i]->get_props();
 	  break;
+	case Or:
+	  {
+	    bool ew = (*v)[0]->accepts_eword();
+	    props = (*v)[0]->get_props();
+	    for (unsigned i = 1; i < s; ++i)
+	      {
+		ew |= (*v)[i]->accepts_eword();
+		props &= (*v)[i]->get_props();
+	      }
+	    is.accepting_eword = ew;
+	    break;
+	  }
 	}
     }
 
@@ -280,21 +289,20 @@ namespace spot
 		++i;
 	      }
 	  }
-	// We have    a* & [*0] & 0  = 0  // already checked above
-	//     but    a* & [*0] & c* = [*0]
-	// So if [*0] has been seen, check if all term recognize the
+	// We have    a* & [*0] & c  = 0
+	//     and    a* & [*0] & c* = [*0]
+	// So if [*0] has been seen, check if alls term recognize the
 	// empty word.
 	if (weak_abs_seen)
 	  {
-	    bool acc_empty = true;
+	    bool acc_eword = true;
 	    for (i = v->begin(); i != v->end(); ++i)
 	      {
-		if (acc_empty)
-		  acc_empty = constant_term_as_bool(*i);
+		acc_eword &= (*i)->accepts_eword();
 		(*i)->destroy();
 	      }
 	    delete v;
-	    if (acc_empty)
+	    if (acc_eword)
 	      return weak_abs;
 	    else
 	      return constant::false_instance();

src/ltlast/unop.cc

@@ -40,34 +40,40 @@ namespace spot
 	{
 	case Not:
 	  is.in_nenoform = !!dynamic_cast<atomic_prop*>(child);
+	  is.accepting_eword = false;
 	  break;
 	case X:
 	  is.boolean = false;
 	  is.X_free = false;
 	  is.eltl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	case F:
 	  is.boolean = false;
 	  is.eltl_formula = false;
 	  is.sugar_free_ltl = false;
 	  is.eventual = true;
+	  is.accepting_eword = false;
 	  break;
 	case G:
 	  is.boolean = false;
 	  is.eltl_formula = false;
 	  is.sugar_free_ltl = false;
 	  is.universal = true;
+	  is.accepting_eword = false;
 	  break;
 	case Finish:
 	  is.boolean = false;
 	  is.ltl_formula = false;
 	  is.psl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	case Closure:
 	case NegClosure:
 	  is.boolean = false;
 	  is.ltl_formula = false;
 	  is.eltl_formula = false;
+	  is.accepting_eword = false;
 	  break;
 	}
     }