Introduce rational operators and trivial simplification rules.

Trivial simplifications rules (such as "FFa=Fa" or "x&1=x")
are performed any time a formule is instanciated.

* src/ltlast/constant.hh, src/ltlast/constant.cc
(true_instance, true_instance_): Declare the true_instance_ as a
static member, and move true_instance() into the .hh so it gets
inlined.  Have true_instance_ as a class variable will ensure that
it is the first formula instantiated.  Binop simplifications rely
on this to order arguments.
(false_instance, false_instance_): Likewise.
(empty_word_instance, empty_word_instance_): New method and static
member.
* src/ltlast/formula.hh (formula::formula): If max_count_ ever
loops, skip the first three values so that constants always have
smaller hash codes.
* src/ltlast/binop.hh, src/ltlast/binop.cc (instance): Add
simplifications and document them.
* src/ltlast/multop.hh (multop::Concat): New operator.
* src/ltlast/multop.cc (op_name): Handle Concat.
(instance): Inline Concat arguments without reordering.  Handle
absorbent and neutral elements for all operators.
* src/ltlast/unop.hh (unop::Star): New operator.
* src/ltlast/unop.cc (op_name): Handle Star.
(instance): Handle Star, and add trivial simplifications for
other unary operators.
* src/ltlparse/ltlparse.yy (OP_CONCAT, OP_STAR, CONST_EMPTYWORD):
Declare these new operators and add rules for them.
* src/ltlparse/ltlscan.ll (OP_CONCAT, OP_STAR, CONST_EMPTYWORD):
Output these new operators.
* src/ltltest/equals.test: New tests.
* src/ltltest/parse.test: Remove redundant test.
* src/ltltest/tunabbrev.test, src/tgbatest/emptchk.test: Adjust tests.
* src/ltlvisit/basicreduce.cc, src/ltlvisit/contain.cc,
src/ltlvisit/nenoform.cc, src/ltlvisit/reduce.cc,
src/ltlvisit/syntimpl.cc, src/ltlvisit/tostring.cc,
src/ltlvisit/tunabbrev.cc: Complete visitors to handle new
operators.
* src/ltltest/nenoform.test: More tests.
* src/ltlvisit/lunabbrev.cc (unabbreviate_logic_visitor::visit):
Clone formulae before instance() function actually have a chance
to destroy them.
* src/tgba/formula2bdd.cc, src/tgbaalgos/eltl2tgba_lacim.cc,
src/tgbaalgos/ltl2taa.cc, src/tgbaalgos/ltl2tgba_fm.cc,
src/tgbaalgos/ltl2tgba_lacim.cc: Adjust switches to assert on new
operators.

src/ltlast/unop.hh

@@ -1,8 +1,8 @@
-// Copyright (C) 2009 Laboratoire de Recherche et Développement
+// Copyright (C) 2009, 2010 Laboratoire de Recherche et D<>veloppement
 // de l'Epita (LRDE).
 // Copyright (C) 2003, 2004 Laboratoire d'Informatique de Paris
-// 6 (LIP6), département Systèmes Répartis Coopératifs (SRC),
-// Université Pierre et Marie Curie.
+// 6 (LIP6), d<EFBFBD>partement Syst<73>mes R<>partis Coop<6F>ratifs (SRC),
+// Universit<EFBFBD> Pierre et Marie Curie.
 //
 // This file is part of Spot, a model checking library.
 //
@@ -40,11 +40,40 @@ namespace spot
     class unop : public ref_formula
     {
     public:
-      enum type { Not, X, F, G, Finish }; // Finish is used in ELTL formulae.
+      enum type {
+	// LTL
+	Not, X, F, G,
+	// ELTL
+	Finish,
+	// Kleene Star
+	Star,
+	};
 
-      /// Build an unary operator with operation \a op and
+      /// \brief Build an unary operator with operation \a op and
       /// child \a child.
-      static unop* instance(type op, formula* child);
+      ///
+      /// The following trivial simplifications are performed
+      /// automatically (the left expression is rewritten as the right
+      /// expression):
+      ///   - 0* = #e
+      ///   - #e* = #e
+      ///   - Exp** = Exp*
+      ///   - FF(Exp) = F(Exp)
+      ///   - GG(Exp) = G(Exp)
+      ///   - F(0) = 0
+      ///   - G(0) = 0
+      ///   - F(1) = 1
+      ///   - G(1) = 1
+      ///   - F(#e) = 1
+      ///   - G(#e) = 1
+      ///   - !1 = 0
+      ///   - !0 = 1
+      ///   - !!Exp = Exp
+      ///
+      /// This rewriting implies that it is not possible to build an
+      /// LTL formula object that is SYNTACTICALLY equal to one of
+      /// these left expressions.
+      static formula* instance(type op, formula* child);
 
       virtual void accept(visitor& v);
       virtual void accept(const_visitor& v) const;