Adding DateTime and Timespan support

src/NReco.LambdaParser.Tests/LambdaParserTests.cs

@@ -25,6 +25,10 @@ public class LambdaParserTests {
 			varContext["nullVar"] = null;
 			varContext["name_with_underscore"] = "a_b";
 			varContext["_name_with_underscore"] = "_a_b";
+			varContext["day1"] = new DateTime().AddDays(1);
+			varContext["day2"] = new DateTime().AddDays(2);
+			varContext["oneDay"] = new TimeSpan(1,0,0,0);
+			varContext["twoDays"] = new TimeSpan(2,0,0,0);
 			return varContext;
 		}
 
@@ -102,6 +106,20 @@ public class LambdaParserTests {
 
 			Assert.True((bool)lambdaParser.Eval("5>two && (5>7 || test.Contains(\"t\") )", varContext));
 			Assert.True((bool)lambdaParser.Eval("null!=test && test!=null && test.Contains(\"t\") && true == Yes && false==!Yes && false!=Yes", varContext));
+
+			Assert.Equal(new DateTime().AddDays(2), lambdaParser.Eval("day1 + oneDay", varContext));
+			Assert.Equal(new DateTime().AddDays(2), lambdaParser.Eval("oneDay + day1", varContext));
+			Assert.Equal(new DateTime().AddDays(1), lambdaParser.Eval("day2 - oneDay", varContext));
+			Assert.Equal(new DateTime().AddDays(1), lambdaParser.Eval("day2 + -oneDay", varContext));
+			Assert.Equal(new DateTime().AddDays(1), lambdaParser.Eval("-oneDay + day2", varContext));
+			Assert.Equal(new TimeSpan(1,0,0,0), lambdaParser.Eval("day2 - day1", varContext));
+			Assert.Equal(new TimeSpan(1,0,0,0).Negate(), lambdaParser.Eval("day1 - day2", varContext));
+			Assert.Equal(new TimeSpan(1,0,0,0), lambdaParser.Eval("day2 - day1", varContext));
+			Assert.Equal(new TimeSpan(2,0,0,0), lambdaParser.Eval("oneDay + oneDay", varContext));
+			Assert.Equal(new TimeSpan(1,0,0,0), lambdaParser.Eval("twoDays - oneDay", varContext));
+			Assert.Equal(new TimeSpan(1,0,0,0), lambdaParser.Eval("twoDays + -oneDay", varContext));
+			Assert.Equal(new TimeSpan(1,0,0,0).Negate(), lambdaParser.Eval("oneDay - twoDays", varContext));
+			Assert.Equal(new TimeSpan(1,0,0,0).Negate(), lambdaParser.Eval("-twoDays + oneDay", varContext));
 		}
 
 		[Fact]

src/NReco.LambdaParser.Tests/ValueComparerTests.cs

@@ -32,6 +32,14 @@ public class ValueComparerTests {
 			Assert.Equal(cmp.Compare(5, null), 1);
 			Assert.Equal(cmp.Compare(null, 0), -1);
 			Assert.Equal(cmp.Compare(null, null), 0);  // two nulls are equal like in C#
+
+			Assert.Equal(cmp.Compare(new DateTime(), new DateTime().AddDays(1)), -1);
+			Assert.Equal(cmp.Compare(new DateTime().AddDays(1), new DateTime()), 1);
+			Assert.Equal(cmp.Compare(new DateTime(), new DateTime()), 0);
+
+			Assert.Equal(cmp.Compare(new TimeSpan(), new TimeSpan()), 0);
+			Assert.Equal(cmp.Compare(new TimeSpan(), new TimeSpan(0,0,1)), -1);
+			Assert.Equal(cmp.Compare(new TimeSpan(0,0,1), new TimeSpan()), 1);
 		}
 
 		[Fact]

src/NReco.LambdaParser/Linq/LambdaParameterWrapper.cs

@@ -186,20 +186,55 @@ internal sealed class LambdaParameterWrapper : IComparable {
 		public static LambdaParameterWrapper operator +(LambdaParameterWrapper c1, LambdaParameterWrapper c2) {
 			if (c1.Value is string || c2.Value is string) {
 				return new LambdaParameterWrapper( Convert.ToString(c1.Value) + Convert.ToString(c2.Value), c1.Cmp);
-			} else {
-				var c1decimal = Convert.ToDecimal(c1.Value, CultureInfo.InvariantCulture);
-				var c2decimal = Convert.ToDecimal(c2.Value,  CultureInfo.InvariantCulture);
-				return new LambdaParameterWrapper(c1decimal + c2decimal, c1.Cmp);
+			} 
+
+			if (c1.Value is TimeSpan c1TimeSpan && c2.Value is DateTime c2DateTime) 
+			{
+				return new LambdaParameterWrapper(c2DateTime.Add(c1TimeSpan), c1.Cmp);
+			}
+
+			if (c1.Value is DateTime c1DateTime && c2.Value is TimeSpan c2TimeSpan) 
+			{
+				return new LambdaParameterWrapper(c1DateTime.Add(c2TimeSpan), c1.Cmp);
 			}
+
+			if (c1.Value is TimeSpan c1ts && c2.Value is TimeSpan c2ts)
+			{
+				return new LambdaParameterWrapper(c1ts + c2ts, c1.Cmp);
+			}
+
+			var c1decimal = Convert.ToDecimal(c1.Value, CultureInfo.InvariantCulture);
+			var c2decimal = Convert.ToDecimal(c2.Value,  CultureInfo.InvariantCulture);
+			return new LambdaParameterWrapper(c1decimal + c2decimal, c1.Cmp);
 		}
 
 		public static LambdaParameterWrapper operator -(LambdaParameterWrapper c1, LambdaParameterWrapper c2) {
+			if (c1.Value is TimeSpan c1ts && c2.Value is TimeSpan c2ts)
+			{
+				return new LambdaParameterWrapper(c1ts - c2ts, c1.Cmp);
+			}
+
+			if (c1.Value is DateTime c1dt && c2.Value is DateTime c2dt)
+			{
+				return new LambdaParameterWrapper(c1dt - c2dt, c1.Cmp);
+			}
+
+			if (c1.Value is DateTime c1DateTime && c2.Value is TimeSpan c2TimeSpan) 
+			{
+				return new LambdaParameterWrapper(c1DateTime.Add(c2TimeSpan.Negate()), c1.Cmp);
+			}
+
 			var c1decimal = Convert.ToDecimal(c1.Value, CultureInfo.InvariantCulture);
 			var c2decimal = Convert.ToDecimal(c2.Value, CultureInfo.InvariantCulture);
 			return new LambdaParameterWrapper(c1decimal - c2decimal, c1.Cmp);
 		}
 
 		public static LambdaParameterWrapper operator -(LambdaParameterWrapper c1) {
+			if(c1.Value is TimeSpan ts)
+			{
+				return new LambdaParameterWrapper(ts.Negate(), c1.Cmp);
+			}
+
 			var c1decimal = Convert.ToDecimal(c1.Value, CultureInfo.InvariantCulture);
 			return new LambdaParameterWrapper(-c1decimal, c1.Cmp);
 		}