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authorsimonmar <unknown>2002-06-03 14:16:56 +0000
committersimonmar <unknown>2002-06-03 14:16:56 +0000
commit466922c82316cecf75a3cc7b31e9331a60c40625 (patch)
tree1201f34a27588d24719a0fc102171e8d9ff7f58a /examples
parent854f4914bf3b9678f1be84c44db7993103d53a01 (diff)
[haddock @ 2002-06-03 14:16:56 by simonmar]
Example from the paper
Diffstat (limited to 'examples')
-rw-r--r--examples/Hash.hs45
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+{- |
+ Implementation of fixed-size hash tables, with a type
+ class for constructing hash values for structured types.
+-}
+module Hash (
+ -- * The @HashTable@ type
+ HashTable,
+
+ -- ** Operations on @HashTable@s
+ new, insert, lookup,
+
+ -- * The @Hash@ class
+ Hash(..),
+ ) where
+
+import Array
+
+-- | A hash table with keys of type @key@ and values of type @val@.
+-- The type @key@ should be an instance of 'Eq'.
+data HashTable key val = HashTable Int (Array Int [(key,val)])
+
+-- | Builds a new hash table with a given size
+new :: (Eq key, Hash key) => Int -> IO (HashTable key val)
+
+-- | Inserts a new element into the hash table
+insert :: (Eq key, Hash key) => key -> val -> IO ()
+
+-- | Looks up a key in the hash table, returns @'Just' val@ if the key
+-- was found, or 'Nothing' otherwise.
+lookup :: Hash key => key -> IO (Maybe val)
+
+-- | A class of types which can be hashed.
+class Hash a where
+ -- | hashes the value of type @a@ into an 'Int'
+ hash :: a -> Int
+
+instance Hash Int where
+ hash = id
+
+instance Hash Float where
+ hash = trunc
+
+instance (Hash a, Hash b) => Hash (a,b) where
+ hash (a,b) = hash a `xor` hash b
+