Formula to string added

Former-commit-id: 53eb9bb5b4

src/logic/Formula.cpp

@@ -1,4 +1,5 @@
 #include "src/logic/Formulas.h"
+#include <sstream>
 
 namespace storm {
     namespace logic {
@@ -404,6 +405,12 @@ namespace storm {
             return;
         }
         
+        std::string Formula::toString() const {
+            std::stringstream str2;
+            writeToStream(str2);
+            return str2.str();
+        }
+        
         std::ostream& operator<<(std::ostream& out, Formula const& formula) {
             return formula.writeToStream(out);
         }

src/logic/Formula.h

@@ -174,6 +174,7 @@ namespace storm {
             std::shared_ptr<Formula const> asSharedPointer();
             std::shared_ptr<Formula const> asSharedPointer() const;
             
+            std::string toString() const;
             virtual std::ostream& writeToStream(std::ostream& out) const = 0;
             
             virtual void gatherAtomicExpressionFormulas(std::vector<std::shared_ptr<AtomicExpressionFormula const>>& atomicExpressionFormulas) const;