title: Concatenating bits in VHDL
body: <p>How do you concatenate bits in VHDL? I'm trying to use the following code:</p>
  
  <p>Case b0 &amp; b1 &amp; b2 &amp; b3 is 
   ...</p>
  
  <p>and it throws an error</p>
  
  <p>Thanks</p>