5.2 The Typeable class

To ease the construction of Dynamic values, we introduce the following type class to help working with TypeReps:

class Typeable a where
  typeOf :: a -> TypeRep

• The typeOf function is overloaded to return the type representation associated with a type.
• Important: The argument to typeOf is only used to carry type information around so that overloading can be resolved. Typeable instances should never, ever look at this argument.
• The Dynamic library provide Typeable instances for all Prelude and Hugs/GHC extension library types. They are:

  Prelude types: 
     Int, Char, Bool, Float, Double, Integer, (IO a),
     [a], (Either a b), (Maybe a), (a->b), 
     (), (,), (,,), (,,,), (,,,,),
     Ordering, Complex, Array, Handle
  Hugs/GHC types:
     Addr, Word8, Word16, Word32, Word64,
     Int8,Int16,Int32,Int64,
     ForeignObj, MVar, (ST s a), (StablePtr a)
  GHC types:
     Word, ByteArray, MutableByteArray