Parse lambda expressions

Parser.Tests/MParserShould.cs

@@ -356,9 +356,23 @@ namespace Parser.Tests
             var text = "@sqrt";
             var sut = CreateParser(text);
             var actual = sut.ParseExpression();
-            Assert.IsInstanceOf<FunctionHandleNode>(actual);
-            var f = (FunctionHandleNode) actual;
+            Assert.IsInstanceOf<NamedFunctionHandleNode>(actual);
+            var f = (NamedFunctionHandleNode) actual;
             Assert.AreEqual("sqrt", f.IdentifierName.Token.PureToken.LiteralText);
+            Assert.AreEqual(text, actual.FullText);            
+        }
+
+        [Test]
+        public void ParseLambda()
+        {
+            var text = "@(x, y) x + y";
+            var sut = CreateParser(text);
+            var actual = sut.ParseExpression();
+            Assert.IsInstanceOf<LambdaNode>(actual);
+            var f = (LambdaNode) actual;
+            Assert.AreEqual(2, f.Input.Parameters.Parameters.Count);
+            Assert.IsInstanceOf<BinaryOperationExpressionNode>(f.Body);
+            Assert.AreEqual(text, actual.FullText);            
         }
     }
 }

Parser/MParser.cs

@@ -553,10 +553,19 @@ namespace Parser
         private FunctionHandleNode ParseFunctionHandle()
         {
             var atSign = EatToken();
-            var identifierName = EatToken(TokenKind.Identifier);
-            return Factory.FunctionHandle(
-                Factory.Token(atSign),
-                Factory.IdentifierName(identifierName));
+            if (CurrentToken.Kind == TokenKind.Identifier)
+            {
+                var identifierName = EatToken(TokenKind.Identifier);
+                return Factory.NamedFunctionHandle(
+                    Factory.Token(atSign),
+                    Factory.IdentifierName(identifierName));
+            } else if (CurrentToken.Kind == TokenKind.OpeningBracket)
+            {
+                var inputs = ParseFunctionInputDescription();
+                var body = ParseExpression();
+                return Factory.Lambda(Factory.Token(atSign), inputs, body);
+            }
+            throw new ParsingException($"Unexpected token {CurrentToken.PureToken} while parsing function handle at {CurrentToken.PureToken.Position}.");
         }
         
         private ExpressionNode ParseSubExpression(ParseOptions options, Precedence precedence)

Parser/SyntaxFactory.cs

@@ -542,7 +542,7 @@ namespace Parser
             return result;
         }
         
-        public FunctionHandleNode FunctionHandle(
+        public NamedFunctionHandleNode NamedFunctionHandle(
             TokenNode atSign,
             IdentifierNameNode identifierName)
         {
@@ -551,7 +551,7 @@ namespace Parser
                 atSign,
                 identifierName
             };
-            var result = new FunctionHandleNode(
+            var result = new NamedFunctionHandleNode(
                 children,
                 atSign,
                 identifierName);
@@ -559,5 +559,24 @@ namespace Parser
             return result;
         }
 
+        public LambdaNode Lambda(
+            TokenNode atSign,
+            FunctionInputDescriptionNode input,
+            ExpressionNode body)
+        {
+            var children = new List<SyntaxNode>
+            {
+                atSign,
+                input,
+                body
+            };
+            var result = new LambdaNode(
+                children,
+                atSign,
+                input,
+                body);
+            SetParent(result);
+            return result;
+        }
     }
 }

Parser/SyntaxNode.cs

@@ -587,12 +587,20 @@ namespace Parser
         }
     }
     
-    public class FunctionHandleNode : ExpressionNode
+    public abstract class FunctionHandleNode : ExpressionNode
+    {
+        protected FunctionHandleNode(
+            List<SyntaxNode> children) : base(children)
+        {
+        }
+    }
+
+    public class NamedFunctionHandleNode : FunctionHandleNode
     {
         public TokenNode AtSign { get; }
         public IdentifierNameNode IdentifierName { get; }
 
-        public FunctionHandleNode(
+        public NamedFunctionHandleNode(
             List<SyntaxNode> children,
             TokenNode atSign,
             IdentifierNameNode identifierName) : base(children)
@@ -602,5 +610,21 @@ namespace Parser
         }
     }
 
+    public class LambdaNode : FunctionHandleNode
+    {
+        public TokenNode AtSign { get; }
+        public FunctionInputDescriptionNode Input { get; }
+        public ExpressionNode Body { get; }
 
+        public LambdaNode(
+            List<SyntaxNode> children,
+            TokenNode atSign,
+            FunctionInputDescriptionNode input,
+            ExpressionNode body) : base(children)
+        {
+            AtSign = atSign;
+            Input = input;
+            Body = body;
+        }
+    }
 }