ungrey first part of Linked

src/exercises/linked.md

@@ -15,12 +15,20 @@ struct Linked<'a, F> {
 }
 
 impl<'a, F: FnMut(String)> Linked<'a, F> {
-# /*
+# fn __() {
+# mod __ {
+# struct Node<'a> { next: Option<Box<Self>>, value: &'a str }
+# struct Linked<'a, F> { node: Box<Node<'a>>, callback: &'a mut F }
+# impl<F> Linked<'_, F> {
     fn with(&mut self, value: &str) -> Linked<'_, F> {
+# unimplemented!() } fn with2(self) { let _ =
         Self {
             node: Node {
                 next: Some(self.node),
-# */
+# value: unimplemented!(),
+# }.into(),
+# callback: self.callback,
+# }; } } } }
 # fn with<'b>(&'b mut self, value: &'b str) -> Linked<'b, F> {
 # Linked {
 # node: Node {