Parse function handles

Parser.Tests/MParserShould.cs

@@ -350,5 +350,15 @@ namespace Parser.Tests
             Assert.AreEqual(text, actual.FullText);            
         }
 
+        [Test]
+        public void ParseFunctionHandle()
+        {
+            var text = "@sqrt";
+            var sut = CreateParser(text);
+            var actual = sut.ParseExpression();
+            Assert.IsInstanceOf<FunctionHandleNode>(actual);
+            var f = (FunctionHandleNode) actual;
+            Assert.AreEqual("sqrt", f.IdentifierName.Token.PureToken.LiteralText);
+        }
     }
 }

Parser/MParser.cs

@@ -549,6 +549,15 @@ namespace Parser
                     throw new ArgumentException(nameof(kind));
             }
         }
+
+        private FunctionHandleNode ParseFunctionHandle()
+        {
+            var atSign = EatToken();
+            var identifierName = EatToken(TokenKind.Identifier);
+            return Factory.FunctionHandle(
+                Factory.Token(atSign),
+                Factory.IdentifierName(identifierName));
+        }
         
         private ExpressionNode ParseSubExpression(ParseOptions options, Precedence precedence)
         {
@@ -561,6 +570,10 @@ namespace Parser
                 var operand = ParseSubExpression(options, newPrecedence);
                 lhs = Factory.UnaryPrefixOperationExpression(Factory.Token(operation), operand);
             }
+            else if (CurrentToken.Kind == TokenKind.At)
+            {
+                return ParseFunctionHandle();
+            }
             else
             {
                 lhs = ParseTerm(options);

Parser/SyntaxFactory.cs

@@ -541,5 +541,23 @@ namespace Parser
             SetParent(result);
             return result;
         }
+        
+        public FunctionHandleNode FunctionHandle(
+            TokenNode atSign,
+            IdentifierNameNode identifierName)
+        {
+            var children = new List<SyntaxNode>
+            {
+                atSign,
+                identifierName
+            };
+            var result = new FunctionHandleNode(
+                children,
+                atSign,
+                identifierName);
+            SetParent(result);
+            return result;
+        }
+
     }
 }

Parser/SyntaxNode.cs

@@ -586,4 +586,21 @@ namespace Parser
             ClosingBracket = closingBracket;
         }
     }
+    
+    public class FunctionHandleNode : ExpressionNode
+    {
+        public TokenNode AtSign { get; }
+        public IdentifierNameNode IdentifierName { get; }
+
+        public FunctionHandleNode(
+            List<SyntaxNode> children,
+            TokenNode atSign,
+            IdentifierNameNode identifierName) : base(children)
+        {
+            AtSign = atSign;
+            IdentifierName = identifierName;
+        }
+    }
+
+
 }