Creative way to represent Biblical references in Haskell.

Reference.hs

-- |A list of `Range's. This is the comprehensive ref type, and
-- can form an arbitrarily complex reference to the scripture.

data Reference = Reference [Range] -- [ x ] means list of x's
  deriving (Show, Eq)

-- |A Range of verses, or a single ref. "Range" is a bit of a misnomer,
-- since we can have a single reference "Range".
data Range
    = Range
        { startAt :: Ref  -- e.g., Rom. 7-9, Gen 3:6-Ex 5:2
        , endAt :: Ref }
    | SingleRef           -- vertical bar | means either/or
        { at :: Ref }     -- e.g. Gen 5:4
  deriving (Eq)

-- |A single Ref. Chapter and verse are represened with 
-- OrdinableInt which are "magic" 
-- integers with two extra values: First and Last.

-- An UnresolvedRef is one with missing information.
-- Perhaps the user didn't feel like typing in the book name or chapter.
-- "Maybe" means it might be missing. We can (usually) figure out what the 
-- user meant, and fill in the Maybes. Then, it turns into a ResolvedRef.

-- A ResolvedRef is one that's got all 3 components. All refs must be converted
-- to this form for most of the internal operations. (E.g., we can't print a verse if
-- we're not sure exactly which one it is.)

data Ref
    = UnresolvedRef -- A @Ref@ which may have pieces missing
        { u_book  :: Maybe BookName               -- e.g. Gen 9, Ps 105, 4:18
        , u_chapt :: Maybe OrdinableInt
        , u_verse :: Maybe OrdinableInt
        }
    | ResolvedRef   -- A unambiguous @Ref@, containing all three components
        { r_book  :: BookName               -- Gen 9:1, Ps 105:3, Cor. 4:17
        , r_chapt :: OrdinableInt
        , r_verse :: OrdinableInt
        }
  deriving (Eq)

-- Just a bit of hocus pocus to encode the concept of "firstness", 
-- "lastness", or "exactly is-ness"
data OrdinableInt
    = OrdinallyFirst   -- the first one, 1
    | Cardinally Int   -- some exact number
    | OrdinallyLast    -- the largest chapter or verse number that makes sense:
                       -- e.g., Gen 50