0.2.2

SharedAssemblyInfo.cs

@@ -0,0 +1,8 @@
+using System.Reflection;
+
+[assembly: AssemblyCompany("VAR")]
+[assembly: AssemblyCopyright("Copyright © VAR 2019-2020")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+[assembly: AssemblyVersion("0.2.2.0")]
+[assembly: AssemblyFileVersion("0.2.2.0")]

VAR.ExpressionEvaluator.Tests/ParserTests.cs

@@ -1,6 +1,6 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
-using System;
 using System.Linq;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace VAR.ExpressionEvaluator.Tests
 {
@@ -171,6 +171,17 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(50m, result);
         }
 
+        [TestMethod()]
+        public void Variables__Var1DivideVar2()
+        {
+            EvaluationContext evaluationContex = new EvaluationContext();
+            evaluationContex.SetVariable("_v1", 100);
+            evaluationContex.SetVariable("$v2", 20);
+            string expression = "_v1 / $v2";
+            object result = Parser.EvaluateString(expression, evaluationContex);
+            Assert.AreEqual(5m, result);
+        }
+
         #endregion Variables
 
         #region Funcitions
@@ -188,6 +199,29 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(10m, result);
         }
 
+        [TestMethod()]
+        public void Functions__NestedTest()
+        {
+            EvaluationContext evaluationContex = new EvaluationContext();
+            evaluationContex.SetVariable("linea1", 1);
+            evaluationContex.SetVariable("linea2", 1);
+            evaluationContex.SetVariable("linea4", 4);
+            evaluationContex.SetFunction("iif", (parameters) =>
+            {
+                if (((bool)parameters[0]) == true)
+                {
+                    return parameters[1];
+                }
+                else
+                {
+                    return parameters[2];
+                }
+            });
+            string expression = "iif(linea1>linea2,iif(linea1>linea4, linea1, iif(linea4>linea2,linea4,linea2)),iif(linea2>linea4,linea2,linea4))";
+            object result = Parser.EvaluateString(expression, evaluationContex);
+            Assert.AreEqual(4m, result);
+        }
+
         #endregion Functions
 
         #region Strings
@@ -266,6 +300,22 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(false, result);
         }
 
+        [TestMethod()]
+        public void Relations_StringEmptyGreatherThan1_EqualsFalse()
+        {
+            string expression = "\"\">1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
+        [TestMethod()]
+        public void Relations_1GreatherThanStringEmpty_EqualsFalse()
+        {
+            string expression = "1>\"\"";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
         [TestMethod()]
         public void Relations_1Equals1_EqualsTrue()
         {
@@ -274,6 +324,22 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(true, result);
         }
 
+        [TestMethod()]
+        public void Relations_StringEmptyEquals1_EqualsFalse()
+        {
+            string expression = "\"\"=1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
+        [TestMethod()]
+        public void Relations_1EqualsStringEmpty_EqualsFalse()
+        {
+            string expression = "1=\"\"";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
         [TestMethod()]
         public void Relations_10NotEquals1_EqualsTrue()
         {
@@ -282,6 +348,46 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(true, result);
         }
 
+        [TestMethod()]
+        public void Relations_StringEmptyNotEquals1_EqualsTrue()
+        {
+            string expression = "\"\"!=1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(true, result);
+        }
+
+        [TestMethod()]
+        public void Relations_1NotEqualsStringEmpty_EqualsTrue()
+        {
+            string expression = "1!=\"\"";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(true, result);
+        }
+
+        [TestMethod()]
+        public void Relations_10Different1_EqualsTrue()
+        {
+            string expression = "10<>1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(true, result);
+        }
+
+        [TestMethod()]
+        public void Relations_StringEmptyDifferent1_EqualsTrue()
+        {
+            string expression = "\"\"<>1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(true, result);
+        }
+
+        [TestMethod()]
+        public void Relations_1DifferentStringEmpty_EqualsTrue()
+        {
+            string expression = "1<>\"\"";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(true, result);
+        }
+
         [TestMethod()]
         public void Relations_10LessThan1_EqualsFalse()
         {
@@ -290,6 +396,22 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(false, result);
         }
 
+        [TestMethod()]
+        public void Relations_StringEmptyLessThan1_EqualsFalse()
+        {
+            string expression = "\"\"<1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
+        [TestMethod()]
+        public void Relations_1LessThanStringEmpty_EqualsFalse()
+        {
+            string expression = "1<\"\"";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
         [TestMethod()]
         public void Relations_1GreaterOrEqualThan1_EqualsTrue()
         {
@@ -298,6 +420,22 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(true, result);
         }
 
+        [TestMethod()]
+        public void Relations_StringEmptyGreaterOrEqualThan1_EqualsFalse()
+        {
+            string expression = "\"\">=1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
+        [TestMethod()]
+        public void Relations_1GreaterOrEqualThanStringEmpty_EqualsFalse()
+        {
+            string expression = "1>=\"\"";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
         [TestMethod()]
         public void Relations_1LessOrEqualThan1_EqualsTrue()
         {
@@ -322,6 +460,22 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(false, result);
         }
 
+        [TestMethod()]
+        public void Relations_StringEmptyLessOrEqualThan1_EqualsFalse()
+        {
+            string expression = "\"\"<=1";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
+        [TestMethod()]
+        public void Relations_1LessOrEqualThanStringEmpty_EqualsFalse()
+        {
+            string expression = "1<=\"\"";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(false, result);
+        }
+
         #endregion Relations
 
         #region BooleanOps
@@ -367,5 +521,45 @@ namespace VAR.ExpressionEvaluator.Tests
 
         #endregion BooleanOps
 
+        #region Null value
+
+
+        [TestMethod()]
+        public void NullValue_NullPlusAnything_EqualsNull()
+        {
+            Assert.AreEqual(null, Parser.EvaluateString("null + 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null + 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 + null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 + null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null + null"));
+        }
+
+        [TestMethod()]
+        public void NullValue_NullMinusAnything_EqualsNull()
+        {
+            Assert.AreEqual(null, Parser.EvaluateString("null - 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null - 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 - null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 - null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null - null"));
+        }
+
+        [TestMethod()]
+        public void NullValue_NullByAnything_EqualsNull()
+        {
+            Assert.AreEqual(null, Parser.EvaluateString("null * 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null * 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 * null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 * null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null * null"));
+
+            Assert.AreEqual(null, Parser.EvaluateString("null / 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null / 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 / null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 / null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null / null"));
+        }
+
+        #endregion
     }
 }

VAR.ExpressionEvaluator.Tests/Properties/AssemblyInfo.cs

@@ -4,12 +4,6 @@ using System.Runtime.InteropServices;
 [assembly: AssemblyTitle("VAR.ExpressionEvaluator.Tests")]
 [assembly: AssemblyDescription("")]
 [assembly: AssemblyConfiguration("")]
-[assembly: AssemblyCompany("")]
 [assembly: AssemblyProduct("VAR.ExpressionEvaluator.Tests")]
-[assembly: AssemblyCopyright("Copyright © VAR 2019")]
-[assembly: AssemblyTrademark("")]
-[assembly: AssemblyCulture("")]
 [assembly: ComVisible(false)]
 [assembly: Guid("3195f0e0-9489-49ce-8fc2-627a73f80cc7")]
-[assembly: AssemblyVersion("0.1.0.0")]
-[assembly: AssemblyFileVersion("0.1.0.0")]

VAR.ExpressionEvaluator.Tests/TokenizerTests.cs

@@ -1,5 +1,5 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System.IO;
-using System.IO;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 
 namespace VAR.ExpressionEvaluator.Tests
 {
@@ -90,9 +90,9 @@ namespace VAR.ExpressionEvaluator.Tests
         }
 
         [TestMethod()]
-        public void Tokenizer__Keywords()
+        public void Tokenizer__Identifiers()
         {
-            var testString = "null true false";
+            var testString = "null true false _$variable1 $variable2 [;{}#]";
             var t = new Tokenizer(new StringReader(testString));
 
             // "null"
@@ -110,6 +110,21 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.AreEqual(t.Text, "false");
             t.NextToken();
 
+            // "_$variable1"
+            Assert.AreEqual(t.Token, Token.Identifier);
+            Assert.AreEqual(t.Text, "_$variable1");
+            t.NextToken();
+
+            // "$variable2"
+            Assert.AreEqual(t.Token, Token.Identifier);
+            Assert.AreEqual(t.Text, "$variable2");
+            t.NextToken();
+
+            // ";{}#"
+            Assert.AreEqual(t.Token, Token.Identifier);
+            Assert.AreEqual(t.Text, ";{}#");
+            t.NextToken();
+
             Assert.AreEqual(t.Token, Token.EOF);
         }
 

VAR.ExpressionEvaluator.Tests/VAR.ExpressionEvaluator.Tests.csproj

@@ -51,6 +51,9 @@
     </Otherwise>
   </Choose>
   <ItemGroup>
+    <Compile Include="..\SharedAssemblyInfo.cs">
+      <Link>Properties\SharedAssemblyInfo.cs</Link>
+    </Compile>
     <Compile Include="ExpressionBinaryNodeTests.cs" />
     <Compile Include="ExpressionNumberNodeTests.cs" />
     <Compile Include="ExpressionStringNodeTests.cs" />

VAR.ExpressionEvaluator/Build.NuGet.cmd

@@ -5,6 +5,7 @@ if exist "%windir%\Microsoft.Net\Framework\v4.0.30319" set MsBuildPath=%windir%\
 if exist "%windir%\Microsoft.Net\Framework64\v4.0.30319" set MsBuildPath=%windir%\Microsoft.NET\Framework64\v4.0.30319
 if exist "C:\Program Files (x86)\MSBuild\14.0\Bin" set MsBuildPath=C:\Program Files (x86)\MSBuild\14.0\Bin
 if exist "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin" set MsBuildPath=C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin
+if exist "C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin" set MsBuildPath=C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin
 set PATH=%MsBuildPath%;%PATH%
 
 echo %MsBuildPath%

VAR.ExpressionEvaluator/EvaluationContext.cs

@@ -39,6 +39,11 @@ namespace VAR.ExpressionEvaluator
 
         public void SetVariable(string name, object value)
         {
+            if (value is DBNull)
+            {
+                value = null;
+            }
+
             if (value is DateTime)
             {
                 value = ((DateTime)value).ToString("s");
@@ -60,7 +65,7 @@ namespace VAR.ExpressionEvaluator
         {
             if (_variables.ContainsKey(name) == false)
             {
-                return null;
+                throw new Exception(string.Format("Variable {0} not found", name));
             }
             return _variables[name];
         }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanAndNode.cs

@@ -9,9 +9,10 @@
 
         private static object BooleanAndOp(object leftValue, object rightValue)
         {
-            bool bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
+            bool? bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
-            bool brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
+            bool? brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
-            return bLeftValue && brightValue;
+            if (bLeftValue == null || bLeftValue == null) { return null; }
+            return bLeftValue.Value && brightValue.Value;
         }
     }
 }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanNode.cs

@@ -14,8 +14,13 @@
             return _value;
         }
 
-        public static bool ConvertToBoolean(object value)
+        public static bool? ConvertToBoolean(object value)
         {
+            if (value == null)
+            {
+                return null;
+            }
+
             if (value is bool)
             {
                 return (bool)value;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanNotNode.cs

@@ -10,6 +10,7 @@
         private static object BooleanNotOp(object value)
         {
             value = ExpressionBooleanNode.ConvertToBoolean(value);
+            if (value == null) { return null; }
             return !(bool)value;
         }
     }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanOrNode.cs

@@ -9,9 +9,10 @@
 
         private static object BooleanOrOp(object leftValue, object rightValue)
         {
-            bool bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
+            bool? bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
-            bool brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
+            bool? brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
-            return bLeftValue || brightValue;
+            if (bLeftValue == null || bLeftValue == null) { return null; }
+            return bLeftValue.Value || brightValue.Value;
         }
     }
 }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionDivisionNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object DivisionOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string)
             {
                 if (decimal.TryParse((string)leftValue, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionEqualsNode.cs

@@ -17,6 +17,12 @@ namespace VAR.ExpressionEvaluator
             }
 
             if (leftValue is string)
+            {
+                if (string.IsNullOrEmpty((string)leftValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)leftValue, out decimal dec) == false)
                     {
@@ -24,7 +30,14 @@ namespace VAR.ExpressionEvaluator
                     }
                     leftValue = dec;
                 }
+            }
             if (rightValue is string)
+            {
+                if (string.IsNullOrEmpty((string)rightValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)rightValue, out decimal dec) == false)
                     {
@@ -32,6 +45,16 @@ namespace VAR.ExpressionEvaluator
                     }
                     rightValue = dec;
                 }
+            }
+
+            if (leftValue == null && rightValue == null)
+            {
+                return true;
+            }
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
 
             if ((leftValue is decimal) == false || (rightValue is decimal) == false)
             {

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionGreaterOrEqualThanNode.cs

@@ -17,6 +17,12 @@ namespace VAR.ExpressionEvaluator
             }
 
             if (leftValue is string)
+            {
+                if (string.IsNullOrEmpty((string)leftValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)leftValue, out decimal dec) == false)
                     {
@@ -24,7 +30,14 @@ namespace VAR.ExpressionEvaluator
                     }
                     leftValue = dec;
                 }
+            }
             if (rightValue is string)
+            {
+                if (string.IsNullOrEmpty((string)rightValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)rightValue, out decimal dec) == false)
                     {
@@ -32,6 +45,12 @@ namespace VAR.ExpressionEvaluator
                     }
                     rightValue = dec;
                 }
+            }
+
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
 
             if ((leftValue is decimal) == false || (rightValue is decimal) == false)
             {

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionGreaterThanNode.cs

@@ -17,6 +17,12 @@ namespace VAR.ExpressionEvaluator
             }
 
             if (leftValue is string)
+            {
+                if (string.IsNullOrEmpty((string)leftValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)leftValue, out decimal dec) == false)
                     {
@@ -24,7 +30,14 @@ namespace VAR.ExpressionEvaluator
                     }
                     leftValue = dec;
                 }
+            }
             if (rightValue is string)
+            {
+                if (string.IsNullOrEmpty((string)rightValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)rightValue, out decimal dec) == false)
                     {
@@ -32,6 +45,12 @@ namespace VAR.ExpressionEvaluator
                     }
                     rightValue = dec;
                 }
+            }
+
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
 
             if ((leftValue is decimal) == false || (rightValue is decimal) == false)
             {

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionLessOrEqualThanNode.cs

@@ -17,6 +17,12 @@ namespace VAR.ExpressionEvaluator
             }
 
             if (leftValue is string)
+            {
+                if (string.IsNullOrEmpty((string)leftValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)leftValue, out decimal dec) == false)
                     {
@@ -24,7 +30,14 @@ namespace VAR.ExpressionEvaluator
                     }
                     leftValue = dec;
                 }
+            }
             if (rightValue is string)
+            {
+                if (string.IsNullOrEmpty((string)rightValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)rightValue, out decimal dec) == false)
                     {
@@ -32,6 +45,12 @@ namespace VAR.ExpressionEvaluator
                     }
                     rightValue = dec;
                 }
+            }
+
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
 
             if ((leftValue is decimal) == false || (rightValue is decimal) == false)
             {

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionLessThanNode.cs

@@ -17,6 +17,12 @@ namespace VAR.ExpressionEvaluator
             }
 
             if (leftValue is string)
+            {
+                if (string.IsNullOrEmpty((string)leftValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)leftValue, out decimal dec) == false)
                     {
@@ -24,7 +30,14 @@ namespace VAR.ExpressionEvaluator
                     }
                     leftValue = dec;
                 }
+            }
             if (rightValue is string)
+            {
+                if (string.IsNullOrEmpty((string)rightValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)rightValue, out decimal dec) == false)
                     {
@@ -32,6 +45,12 @@ namespace VAR.ExpressionEvaluator
                     }
                     rightValue = dec;
                 }
+            }
+
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
 
             if ((leftValue is decimal) == false || (rightValue is decimal) == false)
             {

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionMinusNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object MinusOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string)
             {
                 if (decimal.TryParse((string)leftValue, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionMultiplyNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object MultiplyOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string)
             {
                 if (decimal.TryParse((string)leftValue, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionNotEqualsNode.cs

@@ -17,6 +17,12 @@ namespace VAR.ExpressionEvaluator
             }
 
             if (leftValue is string)
+            {
+                if (string.IsNullOrEmpty((string)leftValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)leftValue, out decimal dec) == false)
                     {
@@ -24,7 +30,14 @@ namespace VAR.ExpressionEvaluator
                     }
                     leftValue = dec;
                 }
+            }
             if (rightValue is string)
+            {
+                if (string.IsNullOrEmpty((string)rightValue))
+                {
+                    leftValue = null;
+                }
+                else
                 {
                     if (decimal.TryParse((string)rightValue, out decimal dec) == false)
                     {
@@ -32,6 +45,16 @@ namespace VAR.ExpressionEvaluator
                     }
                     rightValue = dec;
                 }
+            }
+
+            if (leftValue == null && rightValue == null)
+            {
+                return false;
+            }
+            if (leftValue == null || rightValue == null)
+            {
+                return true;
+            }
 
             if ((leftValue is decimal) == false || (rightValue is decimal) == false)
             {

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionNullNode.cs

@@ -0,0 +1,10 @@
+namespace VAR.ExpressionEvaluator
+{
+    public class ExpressionNullNode : IExpressionNode
+    {
+        public object Eval(IEvaluationContext evaluationContext)
+        {
+            return null;
+        }
+    }
+}

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionNumberNegateNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object NumberNegateOp(object value)
         {
+            if (value == null)
+            {
+                return null;
+            }
+
             if (value is string)
             {
                 if (decimal.TryParse((string)value, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionPlusNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object PlusOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string || rightValue is string)
             {
                 return string.Concat(Convert.ToString(leftValue), Convert.ToString(rightValue));

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionVariableNode.cs

@@ -14,10 +14,6 @@ namespace VAR.ExpressionEvaluator
         public object Eval(IEvaluationContext evaluationContext)
         {
             object value = evaluationContext.GetVariable(_name);
-            if (value == null)
-            {
-                throw new Exception(string.Format("Variable {0} not found", _name));
-            }
             return value;
         }
     }

VAR.ExpressionEvaluator/Parser.cs

@@ -197,6 +197,11 @@ namespace VAR.ExpressionEvaluator
                     _tokenizer.NextToken();
                     return new ExpressionBooleanNode(false);
                 }
+                if (identifierToLower == "null")
+                {
+                    _tokenizer.NextToken();
+                    return new ExpressionNullNode();
+                }
 
                 string identifier = _tokenizer.Text;
                 _tokenizer.NextToken();
@@ -211,7 +216,7 @@ namespace VAR.ExpressionEvaluator
                     var parameters = new List<IExpressionNode>();
                     while (true)
                     {
-                        parameters.Add(ParsePlusAndMinus());
+                        parameters.Add(ParseBooleanOp());
                         if (_tokenizer.Token == Token.Comma)
                         {
                             _tokenizer.NextToken();

VAR.ExpressionEvaluator/Properties/AssemblyInfo.cs

@@ -4,12 +4,6 @@ using System.Runtime.InteropServices;
 [assembly: AssemblyTitle("VAR.ExpressionEvaluator")]
 [assembly: AssemblyDescription("Expression Evaluation Library")]
 [assembly: AssemblyConfiguration("")]
-[assembly: AssemblyCompany("VAR")]
 [assembly: AssemblyProduct("VAR.ExpressionEvaluator")]
-[assembly: AssemblyCopyright("Copyright © VAR 2019")]
-[assembly: AssemblyTrademark("")]
-[assembly: AssemblyCulture("")]
 [assembly: ComVisible(false)]
 [assembly: Guid("74635f68-55b1-4819-84a3-9ea818d396d9")]
-[assembly: AssemblyVersion("0.1.0.0")]
-[assembly: AssemblyFileVersion("0.1.0.0")]

VAR.ExpressionEvaluator/Tokenizer.cs

@@ -144,6 +144,11 @@ namespace VAR.ExpressionEvaluator
                         NextChar();
                         _currentToken = Token.LessOrEqualThan;
                     }
+                    if (_currentChar == '>')
+                    {
+                        NextChar();
+                        _currentToken = Token.NotEquals;
+                    }
                     return;
 
                 case '&':
@@ -171,16 +176,51 @@ namespace VAR.ExpressionEvaluator
             }
 
             // Identifier
-            if (char.IsLetter(_currentChar))
+            if (IsIdentifierStartLetter(_currentChar))
             {
                 var sb = new StringBuilder();
-                while (char.IsLetterOrDigit(_currentChar) || _currentChar == '_')
+                while (IsIdentifierLetter(_currentChar))
                 {
                     sb.Append(_currentChar);
                     NextChar();
                     if (_currentChar == '\0') { break; }
                 }
                 _text = sb.ToString();
+                _currentToken = Token.Identifier;
+            }
+            else if (_currentChar == '[')
+            {
+                char stringEndsWith = ']';
+
+                NextChar();
+                StringBuilder sbString = new StringBuilder();
+                while (_currentChar != stringEndsWith && _currentChar != '\0')
+                {
+                    if (_currentChar != '\\')
+                    {
+                        sbString.Append(_currentChar);
+                    }
+                    else
+                    {
+                        NextChar();
+                        if (_currentChar == stringEndsWith)
+                        {
+                            sbString.Append(stringEndsWith);
+                        }
+                        else
+                        {
+                            // FIXME: Other escaped characters
+                            sbString.Append(_currentChar);
+                        }
+                    }
+                    NextChar();
+                }
+                NextChar();
+                _text = sbString.ToString();
+                _currentToken = Token.Identifier;
+            }
+            if (_currentToken == Token.Identifier)
+            {
                 string textLowercase = _text.ToLower();
                 if (textLowercase == "and")
                 {
@@ -216,7 +256,11 @@ namespace VAR.ExpressionEvaluator
                     else
                     {
                         NextChar();
-                        if (_currentChar == '\\')
+                        if (_currentChar == stringEndsWith)
+                        {
+                            sbString.Append(stringEndsWith);
+                        }
+                        else if (_currentChar == '\\')
                         {
                             sbString.Append('\\');
                         }
@@ -260,5 +304,15 @@ namespace VAR.ExpressionEvaluator
 
             throw new InvalidDataException(string.Format("Unexpected character: {0} at {1}", _currentChar, _currentPosition));
         }
+
+        private static bool IsIdentifierLetter(char c)
+        {
+            return char.IsLetterOrDigit(c) || c == '_' || c == '$' || c == '#' || c == '@';
+        }
+
+        private static bool IsIdentifierStartLetter(char c)
+        {
+            return char.IsLetter(c) || c == '_' || c == '$' || c == '#' || c == '@';
+        }
     }
 }

VAR.ExpressionEvaluator/VAR.ExpressionEvaluator.csproj

@@ -41,6 +41,9 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="..\SharedAssemblyInfo.cs">
+      <Link>Properties\SharedAssemblyInfo.cs</Link>
+    </Compile>
     <Compile Include="EvaluationContext.cs" />
     <Compile Include="ExpressionNodes\ExpressionBooleanAndNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionBooleanNode.cs" />
@@ -55,6 +58,7 @@
     <Compile Include="ExpressionNodes\ExpressionLessThanNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionMultiplyNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionNotEqualsNode.cs" />
+    <Compile Include="ExpressionNodes\ExpressionNullNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionUnaryNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionBinaryNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionMinusNode.cs" />