acc_code: parse from the constructor

* spot/twa/acc.hh, spot/twa/acc.cc (parse_acc_code): Rename as...
(acc_cond::acc_code): ... this, making it a lot easier to build
acceptance conditions from strings.
* NEWS: Mention the change.
* spot/twaalgos/dtwasat.cc, spot/bin/randaut.cc, spot/tests/acc.cc:
Adjust.
* wrap/python/tests/acc_cond.ipynb, wrap/python/tests/accparse.ipynb,
wrap/python/tests/accparse2.py: Simplify, but not completely to exercise
all variants.
* wrap/python/spot_impl.i: Make acc_code's constructor implicit.

spot/bin/randaut.cc

@@ -347,7 +347,7 @@ main(int argc, char** argv)
 	  spot::acc_cond::acc_code code;
 	  if (opt_acceptance)
 	    {
-	      code = spot::parse_acc_code(opt_acceptance);
+	      code = spot::acc_cond::acc_code(opt_acceptance);
 	      accs = code.used_sets().max_set();
 	      if (opt_colored && accs == 0)
 		error(2, 0, "--colored requires at least one acceptance set; "

spot/tests/acc.cc

@@ -158,14 +158,14 @@ int main()
   std::cout << code3 << ' ' << "{0} false\n";
   print(code3.missing(m, false));
 
-  std::cout << spot::parse_acc_code("t") << '\n';
-  std::cout << spot::parse_acc_code("f") << '\n';
-  std::cout << spot::parse_acc_code("Fin(2)") << '\n';
-  std::cout << spot::parse_acc_code("Inf(2)") << '\n';
-  std::cout << spot::parse_acc_code("Fin(2) | Inf(2)") << '\n';
-  std::cout << spot::parse_acc_code("Inf(2) & Fin(2)") << '\n';
-  auto c1 = spot::parse_acc_code("Fin(0)|Inf(1)&Fin(2)|Fin(3)");
-  auto c2 = spot::parse_acc_code
+  std::cout << spot::acc_cond::acc_code("t") << '\n';
+  std::cout << spot::acc_cond::acc_code("f") << '\n';
+  std::cout << spot::acc_cond::acc_code("Fin(2)") << '\n';
+  std::cout << spot::acc_cond::acc_code("Inf(2)") << '\n';
+  std::cout << spot::acc_cond::acc_code("Fin(2) | Inf(2)") << '\n';
+  std::cout << spot::acc_cond::acc_code("Inf(2) & Fin(2)") << '\n';
+  auto c1 = spot::acc_cond::acc_code("Fin(0)|Inf(1)&Fin(2)|Fin(3)");
+  auto c2 = spot::acc_cond::acc_code
     ("(  Fin  (  0 ))  | (Inf   (   1) &  Fin(2 ))| Fin (3)   ");
   std::cout << c1 << '\n';
   std::cout << c2 << '\n';

spot/twa/acc.cc

@@ -1544,7 +1544,7 @@ namespace spot
 
   }
 
-  acc_cond::acc_code parse_acc_code(const char* input)
+  acc_cond::acc_code::acc_code(const char* input)
   {
     skip_space(input);
     acc_cond::acc_code c;
@@ -1630,6 +1630,6 @@ namespace spot
 	s << "syntax error at '" << input << "', unexpected character.";
 	throw parse_error(s.str());
       }
-    return c;
+    std::swap(c, *this);
   }
 }

spot/twa/acc.hh

@@ -889,6 +889,38 @@ namespace spot
 	      std::function<void(std::ostream&, int)>
 	      set_printer = nullptr) const;
 
+
+      /// \brief Construct an acc_code from a string.
+      ///
+      /// The string can follow the following grammar:
+      ///
+      /// <pre>
+      ///   acc ::= "t"
+      ///         | "f"
+      ///         | "Inf" "(" num ")"
+      ///         | "Fin" "(" num ")"
+      ///         | "(" acc ")"
+      ///         | acc "&" acc
+      ///         | acc "|" acc
+      /// </pre>
+      ///
+      /// Where num is an integer and "&" has priority over "|".  Note that
+      /// "Fin(!x)" and "Inf(!x)" are not supported by this parser.
+      ///
+      /// Or the string can be the name of an acceptance condition, as
+      /// speficied in the HOA format.  (E.g. "Rabin 2", "parity max odd 3",
+      /// "generalized-Rabin 4 2 1", etc.).
+      ///
+      /// A spot::parse_error is thrown on syntax error.
+      acc_code(const char* input);
+
+      /// \brief Build an empty acceptance condition.
+      ///
+      /// This is the same as t().
+      acc_code()
+      {
+      }
+
       // Calls to_text
       SPOT_API
       friend std::ostream& operator<<(std::ostream& os, const acc_code& code);
@@ -1167,26 +1199,6 @@ namespace spot
 
   };
 
-  /// \brief Parse a string into an acc_code
-  ///
-  /// The string should follow the following grammar:
-  ///
-  /// <pre>
-  ///   acc ::= "t"
-  ///         | "f"
-  ///         | "Inf" "(" num ")"
-  ///         | "Fin" "(" num ")"
-  ///         | "(" acc ")"
-  ///         | acc "&" acc
-  ///         | acc "|" acc
-  /// </pre>
-  ///
-  /// Where num is an integer and "&" has priority over "|".  Note that
-  /// "Fin(!x)" and "Inf(!x)" are not supported by this parser.
-  ///
-  /// A spot::parse_error is thrown on syntax error.
-  SPOT_API acc_cond::acc_code parse_acc_code(const char* input);
-
   SPOT_API
   std::ostream& operator<<(std::ostream& os, const acc_cond& acc);
 }

spot/twaalgos/dtwasat.cc

@@ -1313,7 +1313,7 @@ namespace spot
     if (!accstr.empty())
       {
 	user_supplied_acc = true;
-	target_acc = parse_acc_code(accstr.c_str());
+	target_acc = acc_cond::acc_code(accstr.c_str());
 	// Just in case we were given something like
 	//  Fin(1) | Inf(3)
 	// Rewrite it as