Small fixes to code samples in Tutorials

doc/tutorial-borrowed-ptr.md

@@ -302,7 +302,7 @@ rejected by the compiler):
 fn example3() -> int {
     let mut x = ~X {f: 3};
     let y = &x.f;
-    x = ~{f: 4};  // Error reported here.
+    x = ~X {f: 4};  // Error reported here.
     *y
 }
 ~~~
@@ -366,12 +366,14 @@ Things get trickier when the unique box is not uniquely owned by the
 stack frame, or when there is no way for the compiler to determine the
 box's owner. Consider a program like this:
 
-~~~
+~~~ {.xfail-test}
 struct R { g: int }
 struct S { mut f: ~R }
-fn example5a(x: @S ...) -> int {
+fn example5a(x: @S, callback: @fn()) -> int {
     let y = &x.f.g;   // Error reported here.
     ...
+    callback();
+    ...
 #   return 0;
 }
 ~~~

doc/tutorial.md

@@ -2015,7 +2015,7 @@ the method name with the trait name.
 The compiler will use type inference to decide which implementation to call.
 
 ~~~~
-# trait Shape { static fn new(area: float) -> self; }
+trait Shape { static fn new(area: float) -> self; }
 # use float::consts::pi;
 # use float::sqrt;
 struct Circle { radius: float }
@@ -2211,11 +2211,15 @@ Likewise, supertrait methods may also be called on trait objects.
 ~~~ {.xfail-test}
 # trait Shape { fn area(&self) -> float; }
 # trait Circle : Shape { fn radius(&self) -> float; }
-# impl int: Shape { fn area(&self) -> float { 0.0 } }
-# impl int: Circle { fn radius(&self) -> float { 0.0 } }
-# let mycircle = 0;
+# use float::consts::pi;
+# use float::sqrt;
+# struct Point { x: float, y: float }
+# struct CircleStruct { center: Point, radius: float }
+# impl CircleStruct: Circle { fn radius(&self) -> float { sqrt(self.area() / pi) } }
+# impl CircleStruct: Shape { fn area(&self) -> float { pi * square(self.radius) } }
 
-let mycircle: Circle = @mycircle as @Circle;
+let concrete = @CircleStruct{center:Point{x:3f,y:4f},radius:5f};
+let mycircle: Circle = concrete as @Circle;
 let nonsense = mycircle.radius() * mycircle.area();
 ~~~