title: Not in scope: data constructor
body: <p>I wrote a program with <code>haskell</code> but I got errors from ghci</p>
  
  <p>here is the source codes,I construct it, and if I have </p>
  
  <pre><code>p1 :: Prop
  p1 = And (Var 'A') (Not (Var 'A'))
  </code></pre>
  
  <p>It will show <code>A &amp;&amp; ~A</code> so that is the source codes</p>
  
  <pre><code>import Data.List
  import Data.Char
  data Prop = Const Bool | 
          Var Char | 
          Not Prop | 
          And Prop Prop | 
          Or Prop Prop | 
          Imply Prop Prop
          deriving Eq
  instance Show Prop where
    show (Var Char) = show Char
    show (Not Prop) = "(~" ++ show Prop ++ ")"
    show (And Prop Prop) = "(" ++ show Prop ++ "&amp;&amp;" ++ show Prop ++ ")"
    show (Or Prop Prop) = "(" ++ show Prop "||" ++ show Prop ++ ")"
    show (Imply Prop Prop) = "(" ++ show Prop "=&gt;" show Prop ++ ")"
  </code></pre>
  
  <p>And I got two main errors from ghci... </p>
  
  <pre><code>Not in scope: data constructor `Char'
  Not in scope: data constructor `Prop'
  </code></pre>
  
  <p>I am a beginner with haskell,thankyou very much.</p>