Parser: Parse number negation.

VAR.ExpressionEvaluator.Tests/ParserTests.cs

@@ -36,5 +36,46 @@ namespace VAR.ExpressionEvaluator.Tests
             object result = Parser.EvaluateString(expression);
             Assert.AreEqual(900000m, result);
         }
+
+        [TestMethod()]
+        public void ParseString__MinusTen()
+        {
+            string expression = "-10";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(-10m, result);
+        }
+
+        [TestMethod()]
+        public void ParseString__PlusTen()
+        {
+            string expression = "+10";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(10m, result);
+        }
+
+        [TestMethod()]
+        public void ParseString__MinusMinusTen()
+        {
+            string expression = "--10";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(10m, result);
+        }
+
+        [TestMethod()]
+        public void ParseString__MinusPlusChainTen()
+        {
+            string expression = "--++-+-10";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(10m, result);
+        }
+
+        [TestMethod()]
+        public void ParseString__10Minus20Minus30()
+        {
+            string expression = "10 + -20 - +30";
+            object result = Parser.EvaluateString(expression);
+            Assert.AreEqual(-40m, result);
+        }
+
     }
 }

VAR.ExpressionEvaluator/ExpressionNumberNegateNode.cs

@@ -0,0 +1,15 @@
+namespace VAR.ExpressionEvaluator
+{
+    public class ExpressionNumberNegateNode : ExpressionUnaryNode
+    {
+        public ExpressionNumberNegateNode(IExpressionNode node) :
+            base(node, NumberNegateOp)
+        {
+        }
+
+        private static object NumberNegateOp(object value)
+        {
+            return - (decimal)value;
+        }
+    }
+}

VAR.ExpressionEvaluator/ExpressionUnaryNode.cs

@@ -0,0 +1,24 @@
+using System;
+
+namespace VAR.ExpressionEvaluator
+{
+    public class ExpressionUnaryNode : IExpressionNode
+    {
+        private IExpressionNode _node;
+        private readonly Func<object, object> _operation;
+
+        public ExpressionUnaryNode(IExpressionNode node, Func<object, object> operation)
+        {
+            _node = node;
+            _operation = operation;
+        }
+
+        public object Eval()
+        {
+            object value = _node.Eval();
+
+            object result = _operation(value);
+            return result;
+        }
+    }
+}

VAR.ExpressionEvaluator/Parser.cs

@@ -26,19 +26,19 @@ namespace VAR.ExpressionEvaluator
 
         public IExpressionNode ParsePlusAndMinus()
         {
-            IExpressionNode leftNode = ParseTerminus();
+            IExpressionNode leftNode = ParseUnary();
             while (true)
             {
                 if (_tokenizer.Token == Token.Plus)
                 {
                     _tokenizer.NextToken();
-                    IExpressionNode rightNode = ParseTerminus();
+                    IExpressionNode rightNode = ParseUnary();
                     leftNode = new ExpressionPlusNode(leftNode, rightNode);
                 }
                 else if (_tokenizer.Token == Token.Minus)
                 {
                     _tokenizer.NextToken();
-                    IExpressionNode rightNode = ParseTerminus();
+                    IExpressionNode rightNode = ParseUnary();
                     leftNode = new ExpressionMinusNode(leftNode, rightNode);
                 }
                 else
@@ -48,6 +48,22 @@ namespace VAR.ExpressionEvaluator
             }
         }
 
+        private IExpressionNode ParseUnary()
+        {
+            if (_tokenizer.Token == Token.Plus)
+            {
+                _tokenizer.NextToken();
+                return ParseUnary();
+            }
+            if (_tokenizer.Token == Token.Minus)
+            {
+                _tokenizer.NextToken();
+                var node = ParseUnary();
+                return new ExpressionNumberNegateNode(node);
+            }
+            return ParseTerminus();
+        }
+
         private IExpressionNode ParseTerminus()
         {
             if (_tokenizer.Token == Token.Number)

VAR.ExpressionEvaluator/VAR.ExpressionEvaluator.csproj

@@ -41,8 +41,10 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="ExpressionUnaryNode.cs" />
     <Compile Include="ExpressionBinaryNode.cs" />
     <Compile Include="ExpressionMinusNode.cs" />
+    <Compile Include="ExpressionNumberNegateNode.cs" />
     <Compile Include="ExpressionPlusNode.cs" />
     <Compile Include="ExpressionStringNode.cs" />
     <Compile Include="ExpressionNumberNode.cs" />