How do I create an operator in Haskell?

Question

Making a ternary logic table, and I would like to make my own function for an operator that I'll call <=>.

So, for example, I want to do this, but that isn't right. what's the correct way to do this?

data Ternary = T | F | M deriving (Eq,  Show, Ord)  <=> :: Ternary -> Ternary -> Ternary <=> T F = F <=> T T = T <=> T M = M <=> F F = T <=> F T = F <=> F M = M <=> M F = M <=> M T = M <=> M M = T 

Answer 1

Just add parentheses around your operator:

(<=>) :: Ternary -> Ternary -> Ternary (<=>) T F = F (<=>) T T = T (<=>) T M = M (<=>) F F = T (<=>) F T = F (<=>) F M = M (<=>) M F = M (<=>) M T = M (<=>) M M = T 

This turns it from infix form to prefix form. Alternatively, you can just use infix in the definition:

(<=>) :: Ternary -> Ternary -> Ternary T <=> F = F T <=> T = T T <=> M = M F <=> F = T F <=> T = F F <=> M = M M <=> F = M M <=> T = M M <=> M = T 

Answer 2

Function names with symbols have different syntax than those without:

-- Works: (<^>) :: Int -> Int -> Int a <^> b = a + b  -- Doesn't work: {- <^> :: Int -> Int -> Int <^> a b = a + b -}  -- Works: letters :: Int -> Int -> Int letters a b = a + b  -- Doesn't work: {- (letters) :: Int -> Int -> Int a letters b = a + b -} 

I promise, though - Haskell is well worth learning the complex rules.