Add test for non-pure function definition

tests/test_ASTNodeFunctionExpressionBuilder.cpp

@@ -1141,5 +1141,98 @@ f((1,2,3),2,3);
         CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{"bad number of arguments: expecting 2, provided 3"});
       }
     }
+
+    SECTION("non pure function")
+    {
+      SECTION("argument modification")
+      {
+        SECTION("++ argument")
+        {
+          std::string_view data = R"(
+let non_pure : R -> R, x -> 3 * ++x;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+
+        SECTION("argument ++")
+        {
+          std::string_view data = R"(
+let non_pure : R -> R, x -> 1 + x ++;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+
+        SECTION("-- argument")
+        {
+          std::string_view data = R"(
+let non_pure : R -> R, x -> 3 * --x;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+
+        SECTION("argument --")
+        {
+          std::string_view data = R"(
+let non_pure : R -> R, x -> 1 + x --;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+      }
+
+      SECTION("outer variable modification")
+      {
+        SECTION("++ outer variable")
+        {
+          std::string_view data = R"(
+let a:R, a = 4;
+let non_pure : R -> R, x -> x * ++a;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+
+        SECTION("outer variable ++")
+        {
+          std::string_view data = R"(
+let a:R, a = 4;
+let non_pure : R -> R, x -> x + a++;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+
+        SECTION("-- outer variable")
+        {
+          std::string_view data = R"(
+let a:R, a = 4;
+let non_pure : R -> R, x -> x * --a;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+
+        SECTION("outer variable --")
+        {
+          std::string_view data = R"(
+let a:R, a = 4;
+let non_pure : R -> R, x -> x + a--;
+)";
+
+          CHECK_EXPRESSION_BUILDER_THROWS_WITH(data, std::string{
+                                                       "invalid function definition. Function data must be constant!"});
+        }
+      }
+    }
   }
 }