Refined the example

src/libcore/macros.rs

@@ -349,34 +349,22 @@ macro_rules! try {
 /// write!(&mut v, "s = {:?}", s).unwrap(); // uses io::Write::write_fmt
 /// assert_eq!(v, b"s = \"abc 123\"");
 /// ```
-
-/// /// Note : This macro can be used in no_std setups as well
-/// /// In a no_std setup you are responsible for the 
-/// /// implementation details of the components.
-
-/// ```rust
-///  extern crate core;
+/// Note : This macro can be used in no_std setups as well
+/// In a no_std setup you are responsible for the 
+/// implementation details of the components.
+/// ```
+///  # extern crate core;
 ///  use core::fmt::Write;
-
-///  #[derive(Debug)]
-///  struct Greetings<'a>{
-///      message : &'a str,
+///  struct Example{
 ///  }
-
-
-///  impl<'a> Write for Greetings<'a>{
+///  impl Write for Example{
 ///      fn write_str(&mut self, _s: &str) -> core::fmt::Result {
 ///           unimplemented!();
 ///      }
 ///  }
-
-///  fn main(){
-///      let mut m = Greetings{message: ""};
+///  let mut m = Example{};
 ///  write!(&mut m, "Hello World").expect("Not written");
-///  }
 /// ```
-
-
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 macro_rules! write {