Rewrites example and text to avoid repetition

This fixes #2237, but also refers to #1924. It's always better to have
two valid examples, than to have a single one.

Another alternative is, of course, to eliminate indexing of one of
them, but this is probably better.

doc/Language/operators.pod6

@@ -1388,26 +1388,28 @@ the C<temp> was undone, you'd get the original value, not the C<temp> one:
 
     sub prefix:<let>(Mu $a is rw)
 
-Restores the previous value if the block exits unsuccessfully. A
-successful exit means the block returned a defined value or a list.
+Refers to a variable in an outer scope whose value will be restored if the block
+exits unsuccessfully, implying that the block returned a defined object.
 
-    my $answer = 42;
+=begin code
+my $name = "Jane Doe";
 
-    {
-        let $answer = 84;
-        die if not Bool.pick;
-        CATCH {
-            default { say "it's been reset :(" }
-        }
-        say "we made it 84 sticks!";
+{
+    let $name = prompt("Say your name ");
+    die if !$name;
+    CATCH {
+        default { say "No name entered" }
     }
+    say "We have $name";
+}
 
-    say $answer;
+say "We got $name";
+=end code
 
-In the above case, if the C<Bool.pick> returns true, the answer will
-stay as 84 because the block returns a defined value (C<say> returns
-true). Otherwise the C<die> statement will cause the block to exit
-unsuccessfully, resetting the answer to 42.
+This code provides a default name for C<$name>. If the user exits from the
+prompt of simply does not provide a valid input for C<$name>; C<let> will
+restore the default value provided at the top. If user input is valid, it will
+keep that.
 
 =comment this is duplicated in variables.pod