title: Haskell - error by execution
body: <p>I try to write a this monad</p>
  
  <pre><code>data W x = W x [String]
  
  instance Monad W where
  return x = W x []
  W a h1 &gt;&gt;= f = case f a of 
      W b h2 -&gt; W b (h1++h2)
  </code></pre>
  
  <p>But, now when i will use this monad and try to write return or >>= in code I get by compilation the warnings:</p>
  
  <blockquote>
    <p>No explicit method nor default method for Prelude.return in the instance declaration.
    No explicit method nor default method for Prelude.>>= in the instance declaration.</p>
  </blockquote>
  
  <p>Does anyone know how to fix this warnings?</p>
  
  <p>thank you very much</p>