Fix functions without parameters.

VAR.ExpressionEvaluator.Tests/ParserTests.cs

@@ -241,6 +241,19 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.Equal(4m, result);
         }
 
+        [Fact]
+        public void Functions__ZeroParameters()
+        {
+            EvaluationContext evaluationContex = new EvaluationContext();
+            evaluationContex.SetFunction("constant", (parameters) =>
+            {
+                return 9m;
+            });
+            string expression = "constant()";
+            object result = Parser.EvaluateString(expression, evaluationContex);
+            Assert.Equal(9m, result);
+        }
+
         #endregion Functions
 
         #region Strings
@@ -253,6 +266,14 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.Equal("Hello World", result);
         }
         
+        [Fact]
+        public void Strings__Contatenate_Hello_World_SimpleQuotes()
+        {
+            string expression = "'Hello' + ' ' +'World'";
+            object result = Parser.EvaluateString(expression);
+            Assert.Equal("Hello World", result);
+        }
+
         [Fact]
         public void Strings__Contatenate_Hello_World_WithVariables()
         {

VAR.ExpressionEvaluator/Parser.cs

@@ -239,6 +239,8 @@ namespace VAR.ExpressionEvaluator
                 {
                     _tokenizer.NextToken();
                     var parameters = new List<IExpressionNode>();
+                    if (_tokenizer.Token != Token.ParenthesisEnd)
+                    {
                         while (true)
                         {
                             parameters.Add(ParseBooleanOp());
@@ -249,6 +251,7 @@ namespace VAR.ExpressionEvaluator
                             }
                             break;
                         }
+                    }
                     if (_tokenizer.Token != Token.ParenthesisEnd)
                     {
                         throw new MissingCloseParenthesisException();