Migrate extend statement parser to Kotlin

src/main/kotlin/dsl/ast/model/node/ExtendNode.kt

@@ -0,0 +1,20 @@
+package dsl.ast.model.node
+
+import dsl.token.model.entity.TokenPosition
+
+class ExtendNode(type: Node, identifier: Node, functions: Node, position: TokenPosition) : Node(3, position) {
+    val type: Node
+    get() = children[0]
+
+    val identifier: Node
+    get() = children[1]
+
+    val functions: Node
+    get() = children[2]
+
+    init {
+        children[0] = type
+        children[1] = identifier
+        children[2] = functions
+    }
+}

src/main/kotlin/dsl/ast/parser/ExtendParser.kt

@@ -0,0 +1,40 @@
+package dsl.ast.parser
+
+import dsl.ast.model.entity.ParserOutput
+import dsl.ast.model.node.BlockNode
+import dsl.ast.model.node.ExtendNode
+import dsl.ast.model.node.Node
+import dsl.token.model.entity.TokenList
+import dsl.token.model.enumeration.TokenType
+
+class ExtendParser : Parser() {
+    override fun tryToParse(input: TokenList): ParserOutput {
+        val simpleExtendParser = allOf(
+            terminal(TokenType.EXTEND),
+            assert(TypeParser(), "type to be extended"),
+            assert(terminal(TokenType.AS), "'as' keyword with identifier"),
+            assert(SimpleIdentifierParser(), "identifier"),
+            terminal(TokenType.WITH),
+            assert(mapNode(FunctionDefinitionParser()) { BlockNode(Node.NONE, listOf(it), Node.NONE) }, "method definition")
+        ) {
+            ExtendNode(it[1], it[3], it[5], it[0].position)
+        }
+
+        val complexExtendParser = allOf(
+            terminal(TokenType.EXTEND),
+            assert(TypeParser(), "type to be extended"),
+            assert(terminal(TokenType.AS), "'as' keyword with identifier"),
+            assert(SimpleIdentifierParser(), "identifier"),
+            assert(loop(terminal(TokenType.OPEN_CURLY), assert(FunctionDefinitionParser(), "method definition or }"), terminal(TokenType.CLOSE_CURLY)) {
+                begin, methods, end -> BlockNode(begin, methods, end)
+            }, "block with methods' definitions or 'with' keyword with single method definition")
+        ) {
+            ExtendNode(it[1], it[3], it[4], it[0].position)
+        }
+
+        return oneOf(
+            simpleExtendParser,
+            complexExtendParser
+        ).parse(input)
+    }
+}