TheBadTheUglyAndTheGood.idr

-- Defining some Maybe values... 
-- These could just as well have been database lookups or something else
x : Maybe Nat
x = Just 42

y : Maybe String
y = Just "hello idris"

z : Maybe Nat
z = Just 4

-- we wish to sum the above values, -but only if all of them exist...

-- we might start out doing it this way.. Typing match case stuff until our fingers fall off..
addStuffBad : Maybe Nat
addStuffBad =
  case x of
       Nothing => Nothing
       (Just x') =>
          case y of
               Nothing => Nothing
               (Just y') =>
                  case z of
                       Nothing => Nothing
                       (Just z') => Just (x' + length y' + z')

-- then we discover the allmighty Bind function.. and carefully count parentheses
addStuffBetter : Maybe Nat
addStuffBetter =
  x >>= (\x' =>
   y >>= (\y' =>
    z >>= (\z' =>
     Just (x' + length y' + z'))))

-- finaly we learn about the existence of the neat do syntax... syntax sugar!, yummy!
addStuffNeat : Maybe Nat
addStuffNeat =
  do x' <- x
     y' <- y
     z' <- z
     pure (x' + length y' + z')