tl: extend F[n:m] and G[n:m] to the case of m=$

Suggested by Victor Khomenko.

* spot/tl/formula.cc, spot/tl/formula.hh, spot/parsetl/parsetl.yy:
Implement this.
* NEWS, doc/tl/tl.tex: Document it.
* tests/core/sugar.test, tests/python/ltlparse.py: Add some tests.

NEWS

@@ -93,6 +93,9 @@ New in spot 2.7.4.dev (not yet released)
     terms of the existing PSL operators.  ##[+] and ##[*] are sugar
     for ##[1:$] and ##[0:$].
 
+  - The F[n:m] and G[n:m] operators introduced in Spot 2.7 now
+    support the case where m=$.
+
   - spot::relabel_apply() makes it easier to reverse the effect
     of spot::relabel() or spot::relabel_bse() on formula.
 

doc/tl/tl.tex

@@ -523,7 +523,7 @@ $\M$, and $\W$ if you are only familiar with $\X$ and $\U$.
 \subsection{Syntactic Sugar}
 
 The syntax on the left is equivalent to the syntax on the right.
-These rewritings taken from the syntax of TSLF~\citep{jacobs.16.synt}
+Some of rewritings taken from the syntax of TSLF~\citep{jacobs.16.synt}
 are performed from left to right when parsing a formula.  They express
 the fact that some formula $f$ has to be true in $n$ steps, or at some
 or all times between $n$ and $m$ steps.
@@ -532,9 +532,11 @@ or all times between $n$ and $m$ steps.
   \XREP{\mvar{n}} f
   & \equiv \underbrace{\X\X\ldots\X}_{\mathclap{\text{\mvar{n} occurrences of~}\X}} f \\
   \FREP{\mvar{n}:\mvar{m}}f
-  & \equiv \underbrace{\vphantom{(}\X\X\ldots\X}_{\mathclap{\text{\mvar{n} occ. of~}\X}} (f \OR \underbrace{\X(f \OR \X(\ldots \OR \X f))}_{\mathclap{\mvar{m}-\mvar{n}\text{~occ. of~}\X}}) \\
+  & \equiv \underbrace{\vphantom{(}\X\X\ldots\X}_{\mathclap{\text{\mvar{n} occ. of~}\X}} (f \OR \underbrace{\X(f \OR \X(\ldots \OR \X f))}_{\mathclap{\mvar{m}-\mvar{n}\text{~occ. of~}\X}})
+  & \FREP{\mvar{n}:}f &\equiv \XREP{\mvar{n}}\F{}f\\
   \GREP{\mvar{n}:\mvar{m}}f
-  & \equiv \underbrace{\vphantom{(}\X\X\ldots\X}_{\mathclap{\text{\mvar{n} occ. of~}\X}} (f \AND \underbrace{\X(f \AND \X(\ldots \AND \X f))}_{\mathclap{\mvar{m}-\mvar{n}\text{~occ. of~}\X}}) \\
+  & \equiv \underbrace{\vphantom{(}\X\X\ldots\X}_{\mathclap{\text{\mvar{n} occ. of~}\X}} (f \AND \underbrace{\X(f \AND \X(\ldots \AND \X f))}_{\mathclap{\mvar{m}-\mvar{n}\text{~occ. of~}\X}})
+  & \GREP{\mvar{n}:}f &\equiv \XREP{\mvar{n}}\G{}f\\
 \end{align*}
 
 \subsection{Trivial Identities (Occur Automatically)}

spot/parsetl/parsetl.yy

@@ -887,6 +887,10 @@ subformula: booleanatom
 	    | OP_FREP OP_SQBKT_NUM OP_SQBKT_SEP OP_SQBKT_NUM OP_SQBKT_CLOSE
               subformula %prec OP_FREP
               { $$ = fnode::nested_unop_range(op::X, op::Or, $2, $4, $6); }
+	    | OP_FREP OP_SQBKT_NUM OP_SQBKT_SEP_unbounded OP_SQBKT_CLOSE
+              subformula %prec OP_FREP
+            { $$ = fnode::nested_unop_range(op::X, op::Or, $2,
+                                            fnode::unbounded(), $5); }
 	    | OP_FREP OP_SQBKT_NUM OP_SQBKT_SEP OP_SQBKT_NUM OP_SQBKT_CLOSE
               error
 	      { missing_right_op($$, @1 + @5, "F[.] operator"); }
@@ -904,6 +908,10 @@ subformula: booleanatom
 	    | OP_GREP OP_SQBKT_NUM OP_SQBKT_SEP OP_SQBKT_NUM OP_SQBKT_CLOSE
               subformula %prec OP_GREP
               { $$ = fnode::nested_unop_range(op::X, op::And, $2, $4, $6); }
+	    | OP_GREP OP_SQBKT_NUM OP_SQBKT_SEP_unbounded OP_SQBKT_CLOSE
+              subformula %prec OP_GREP
+            { $$ = fnode::nested_unop_range(op::X, op::And, $2,
+                                            fnode::unbounded(), $5); }
 	    | OP_GREP OP_SQBKT_NUM OP_SQBKT_CLOSE subformula %prec OP_GREP
               { $$ = fnode::nested_unop_range(op::X, op::And, $2, $2, $4);
                 error_list.emplace_back(@1 + @3,

spot/tl/formula.cc

@@ -1657,11 +1657,14 @@ namespace spot
     const fnode* res = f;
     if (max < min)
       std::swap(min, max);
+    if (max != unbounded())
       for (unsigned i = min; i < max; ++i)
         {
           const fnode* a = f->clone();
           res = fnode::multop(bo, {a, fnode::unop(uo, res)});
         }
+    else
+      res = fnode::unop(bo == op::Or ? op::F : op::G, res);
     for (unsigned i = 0; i < min; ++i)
       res = fnode::unop(uo, res);
     return res;

spot/tl/formula.hh

@@ -906,7 +906,8 @@ namespace spot
 
     /// \brief Construct F[n:m]
     ///
-    /// F[2:3] = XX(a | Xa)
+    /// F[2:3]a = XX(a | Xa)
+    /// F[2:$]a = XXFa
     ///
     /// This syntax is from TSLF; the operator is called next_e![n..m] in PSL.
     static formula F(unsigned min_level, unsigned max_level, const formula& f)
@@ -916,7 +917,8 @@ namespace spot
 
     /// \brief Construct G[n:m]
     ///
-    /// G[2:3] = XX(a & Xa)
+    /// G[2:3]a = XX(a & Xa)
+    /// G[2:$]a = XXGa
     ///
     /// This syntax is from TSLF; the operator is called next_a![n..m] in PSL.
     static formula G(unsigned min_level, unsigned max_level, const formula& f)
@@ -1217,6 +1219,10 @@ namespace spot
     ///
     /// For instance nested_unup_range(op::X, op::Or, 2, 4, a) returns
     /// XX(a | X(a | Xa)).
+    ///
+    /// For `max==unbounded()`, \a uo is repeated \a min times, and
+    /// its child is set to `F(a)` if \a bo is `op::Or` or to `G(a)`
+    /// otherwise.
     static const formula nested_unop_range(op uo, op bo, unsigned min,
                                            unsigned max, formula f)
     {

tests/core/sugar.test

@@ -30,9 +30,13 @@ G[2:4]a
 G[4:2]a
 F[2:4]a
 F[4:2]a
+F[2:$]a
+F[2..]a
 X [4]a | b
 G [2:4] a | b
 G [4:2] a | b
+G [2:] a | b
+G [2..] a | b
 F [2:4] a |  b
 F [4:2]a | F[2:2]b
 F[]a|G[]b|X[]c
@@ -61,9 +65,13 @@ XX(a & X(a & Xa))
 XX(a & X(a & Xa))
 XX(a | X(a | Xa))
 XX(a | X(a | Xa))
+XXFa
+XXFa
 b | XXXXa
 b | XX(a & X(a & Xa))
 b | XX(a & X(a & Xa))
+b | XXGa
+b | XXGa
 b | XX(a | X(a | Xa))
 XX(a | X(a | Xa)) | XXb
 FGa | Gb | XGc
@@ -93,7 +101,7 @@ F[3:1]
 F[3:1][2:1]
 F[a
 G[2:4]
-G[2:]a
+G[2:.]a
 G[4]a
 G[a
 X[2
@@ -163,12 +171,12 @@ syntax error, unexpected end of formula
 missing right operand for "G[.] operator"
 
 ltlfilt:err.in:6: parse error:
->>> G[2:]a
+>>> G[2:.]a
         ^
-syntax error, unexpected closing bracket, expecting $num
+syntax error, unexpected $undefined, expecting closing bracket
 
->>> G[2:]a
+>>> G[2:.]a
-    ^^^^^
+    ^^^^^^
 treating this G[.] as a simple G
 
 ltlfilt:err.in:7: parse error:

tests/python/ltlparse.py

@@ -1,5 +1,5 @@
 # -*- mode: python; coding: utf-8 -*-
-# Copyright (C) 2009-2012, 2014-2017 Laboratoire de Recherche et
+# Copyright (C) 2009-2012, 2014-2017, 2019 Laboratoire de Recherche et
 # Développement de l'Epita (LRDE).
 # Copyright (C) 2003, 2004 Laboratoire d'Informatique de Paris 6 (LIP6),
 # département Systèmes Répartis Coopératifs (SRC), Université Pierre
@@ -199,3 +199,14 @@ for (x, msg) in [('a->', "missing right operand for \"implication operator\""),
     del f9
 
 assert spot.fnode_instances_check()
+
+f = spot.formula_F(2, 4, spot.formula_ap("a"))
+assert f == spot.formula("XX(a | X(a | X(a)))")
+f = spot.formula_G(2, 4, spot.formula_ap("a"))
+assert f == spot.formula("XX(a & X(a & X(a)))")
+f = spot.formula_X(2, spot.formula_ap("a"))
+assert f == spot.formula("XX(a)")
+f = spot.formula_G(2, spot.formula_unbounded(), spot.formula_ap("a"))
+assert f == spot.formula("XXG(a)")
+f = spot.formula_F(2, spot.formula_unbounded(), spot.formula_ap("a"))
+assert f == spot.formula("XXF(a)")