title: Formatting a list of doubles into a string
body: <p>I am trying to format a list of doubles into a string. I would like to turn a list such as:</p>
  
  <pre><code>[0.38, 0.94]
  </code></pre>
  
  <p>into something like:</p>
  
  <pre><code>"aString 0.380  0.940"
  </code></pre>
  
  <p>I have tried:</p>
  
  <pre><code>"aString" ++ map (printf "%7.3f") [0.38, 0.94]
  </code></pre>
  
  <p>and get the feedback:</p>
  
  <pre><code>&lt;interactive&gt;:80:19:
      No instance for (PrintfType Char)
        arising from a use of `printf'
      Possible fix: add an instance declaration for (PrintfType Char)
      In the first argument of `map', namely `(printf "%7.3f")'
      In the second argument of `(++)', namely
        `map (printf "%7.3f") [0.38, 0.94]'
      In the expression: "aString" ++ map (printf "%7.3f") [0.38, 0.94]
  </code></pre>
  
  <p>I've not been able to fix this. I have unable to compose a signature that works. </p>
  
  <p>Thank you</p>