Safe Haskell  SafeInfered 

Generic hashing on trees. We recursively compute hashes of all subtrees, giving fast inequality testing, and a fast, but meaningless (moreorless random) ordering on the set of trees (so that we can put them into Maps).
The way it works is that when we compute the hash of a node, we use the hashes of the children directly; this way, you can also incrementally build up a hashed tree.
 data HashAnn hash f a = HashAnn hash (f a)
 getHash :: HashAnn hash f a > hash
 unHashAnn :: HashAnn hash f a > f a
 type HashMu hash f = Mu (HashAnn hash f)
 topHash :: HashMu hash f > hash
 forgetHash :: Functor f => HashMu hash f > Mu f
 data HashValue hash = HashValue {
 _emptyHash :: hash
 _hashChar :: Char > hash > hash
 _hashHash :: hash > hash > hash
 hashTree :: (Foldable f, Functor f, ShowF f) => HashValue hash > Mu f > HashMu hash f
 hashTreeWith :: (Foldable f, Functor f) => HashValue hash > (f Hole > hash > hash) > Mu f > HashMu hash f
 hashNode :: (Foldable f, Functor f, ShowF f) => HashValue hash > f (HashMu hash f) > HashMu hash f
 hashNodeWith :: (Foldable f, Functor f) => HashValue hash > (f Hole > hash > hash) > f (HashMu hash f) > HashMu hash f
Hashed tree type
Hash annotation (question: should the Hash field be strict? everything else in the library is lazy...)
This is custom datatype instead of reusing Ann
because of the different Eq/Ord instances we need.
HashAnn hash (f a) 
Functor f => Functor (HashAnn hash f)  
Foldable f => Foldable (HashAnn hash f)  
Traversable f => Traversable (HashAnn hash f)  
(ShowF f, Show hash) => ShowF (HashAnn hash f)  
(Ord hash, OrdF f) => OrdF (HashAnn hash f)  
(Eq hash, EqF f) => EqF (HashAnn hash f)  
(Show hash, Show (f a)) => Show (HashAnn hash f a) 
type HashMu hash f = Mu (HashAnn hash f)Source
A tree annotated with hashes of all subtrees. This gives us fast inequality testing,
and fast (but meaningless!) ordering for Map
s.
forgetHash :: Functor f => HashMu hash f > Mu fSource
Interface to the user's hash functions
A concrete hash implementation. We don't use type classes since
 a hash type class does not belong to this library;
 we don't want to restrict the user's design space
Thus we simulate type classes with record types.
HashValue  

Hashing tres
hashTree :: (Foldable f, Functor f, ShowF f) => HashValue hash > Mu f > HashMu hash fSource
This function uses the ShowF
instance to compute
the hash of a node; this way you always have a working
version without writing any additional code.
However, you can also supply your own hash implementation
(which can be more efficient, for example), if you use hashTreeWith
instead.
hashTreeWith :: (Foldable f, Functor f) => HashValue hash > (f Hole > hash > hash) > Mu f > HashMu hash fSource