Improve HashSet API docs. (#267)

- More information in introduction (basic operations, and using HashSet with custom
data types)
- Examples alongside function docs

Author: m-renaud

Data/HashSet.hs

@@ -4,25 +4,94 @@
 #endif
 
 ------------------------------------------------------------------------
--- |
--- Module      :  Data.HashSet
--- Copyright   :  2011 Bryan O'Sullivan
--- License     :  BSD-style
--- Maintainer  :  johan.tibell@gmail.com
--- Stability   :  provisional
--- Portability :  portable
---
--- A set of /hashable/ values.  A set cannot contain duplicate items.
--- A 'HashSet' makes no guarantees as to the order of its elements.
---
--- The implementation is based on /hash array mapped trie/.  A
--- 'HashSet' is often faster than other tree-based set types,
--- especially when value comparison is expensive, as in the case of
--- strings.
---
--- Many operations have a average-case complexity of /O(log n)/.  The
--- implementation uses a large base (i.e. 16) so in practice these
--- operations are constant time.
+{-|
+Module      :  Data.HashSet
+Copyright   :  2011 Bryan O'Sullivan
+License     :  BSD-style
+Maintainer  :  johan.tibell@gmail.com
+Stability   :  provisional
+Portability :  portable
+
+= Introduction
+
+'HashSet' allows you to store /unique/ elements, providing efficient insertion,
+lookups, and deletion. A 'HashSet' makes no guarantees as to the order of its
+elements.
+
+If you are storing sets of "Data.Int"s consider using "Data.IntSet" from the
+<https://hackage.haskell.org/package/containers containers> package.
+
+
+== Examples
+
+All the examples below assume @HashSet@ is imported qualified, and uses the following @dataStructures@ set.
+
+>>> import qualified Data.HashSet as HashSet
+>>> let dataStructures = HashSet.fromList ["Set", "Map", "Graph", "Sequence"]
+
+=== Basic Operations
+
+Check membership in a set:
+
+>>> -- Check if "Map" and "Trie" are in the set of data structures.
+>>> HashSet.member "Map" dataStructures
+True
+>>> HashSet.member "Trie" dataStructures
+False
+
+Add a new entry to the set:
+
+>>> let moreDataStructures = HashSet.insert "Trie" dataStructures
+>>> HashSet.member "Trie" moreDataStructures
+> True
+
+Remove the @\"Graph\"@ entry from the set of data structures.
+
+>>> let fewerDataStructures = HashSet.delete "Graph" dataStructures
+>>> HashSet.toList fewerDataStructures
+["Map","Set","Sequence"]
+
+
+Create a new set and combine it with our original set.
+
+>>> let unorderedDataStructures = HashSet.fromList ["HashSet", "HashMap"]
+>>> HashSet.union dataStructures unorderedDataStructures
+fromList ["Map","HashSet","Graph","HashMap","Set","Sequence"]
+
+=== Using custom data with HashSet
+
+To create a @HashSet@ of your custom type, the type must have instances for
+'Data.Eq.Eq' and 'Data.Hashable.Hashable'. The @Hashable@ typeclass is defined in the
+<https://hackage.haskell.org/package/hashable hashable> package, see the
+documentation for information on how to make your type an instance of
+@Hashable@.
+
+We'll start by setting up our custom data type:
+
+>>> :set -XDeriveGeneric
+>>> import GHC.Generics (Generic)
+>>> import Data.Hashable
+>>> data Person = Person { name :: String, likesDogs :: Bool } deriving (Show, Eq, Generic)
+>>> instance Hashable Person
+
+And now we'll use it!
+
+>>> let people = HashSet.fromList [Person "Lana" True, Person "Joe" False, Person "Simon" True]
+>>> HashSet.filter likesDogs people
+fromList [Person {name = "Simon", likesDogs = True},Person {name = "Lana", likesDogs = True}]
+
+
+== Performance
+
+The implementation is based on /hash array mapped tries/.  A
+'HashSet' is often faster than other 'Data.Ord.Ord'-based set types,
+especially when value comparisons are expensive, as in the case of
+strings.
+
+Many operations have a average-case complexity of /O(log n)/.  The
+implementation uses a large base (i.e. 16) so in practice these
+operations are constant time.
+-}
 
 module Data.HashSet
     (

Data/HashSet/Base.hs

@@ -19,7 +19,7 @@
 -- A set of /hashable/ values.  A set cannot contain duplicate items.
 -- A 'HashSet' makes no guarantees as to the order of its elements.
 --
--- The implementation is based on /hash array mapped trie/.  A
+-- The implementation is based on /hash array mapped tries/.  A
 -- 'HashSet' is often faster than other tree-based set types,
 -- especially when value comparison is expensive, as in the case of
 -- strings.
@@ -36,10 +36,6 @@ module Data.HashSet.Base
     , empty
     , singleton
 
-    -- * Combine
-    , union
-    , unions
-
     -- * Basic interface
     , null
     , size
@@ -50,6 +46,10 @@ module Data.HashSet.Base
     -- * Transformations
     , map
 
+    -- * Combine
+    , union
+    , unions
+
       -- * Difference and intersection
     , difference
     , intersection
@@ -260,24 +260,39 @@ hashSetDataType :: DataType
 hashSetDataType = mkDataType "Data.HashSet.Base.HashSet" [fromListConstr]
 
 -- | /O(1)/ Construct an empty set.
+--
+-- >>> HashSet.empty
+-- fromList []
 empty :: HashSet a
 empty = HashSet H.empty
 
 -- | /O(1)/ Construct a set with a single element.
+--
+-- >>> HashSet.singleton 1
+-- fromList [1]
 singleton :: Hashable a => a -> HashSet a
 singleton a = HashSet (H.singleton a ())
 {-# INLINABLE singleton #-}
 
--- | /O(1)/ Convert to the equivalent 'HashMap'.
+-- | /O(1)/ Convert to set to the equivalent 'HashMap' with @()@ values.
+--
+-- >>> HashSet.toMap (HashSet.singleton 1)
+-- fromList [(1,())]
 toMap :: HashSet a -> HashMap a ()
 toMap = asMap
 
--- | /O(1)/ Convert from the equivalent 'HashMap'.
+-- | /O(1)/ Convert from the equivalent 'HashMap' with @()@ values.
+--
+-- >>> HashSet.fromMap (HashMap.singleton 1 ())
+-- fromList [1]
 fromMap :: HashMap a () -> HashSet a
 fromMap = HashSet
 
 -- | /O(n)/ Produce a 'HashSet' of all the keys in the given 'HashMap'.
 --
+-- >>> HashSet.keysSet (HashMap.fromList [(1, "a"), (2, "b")]
+-- fromList [1,2]
+--
 -- @since 0.2.10.0
 keysSet :: HashMap k a -> HashSet k
 keysSet m = fromMap (() <$ m)
@@ -287,8 +302,6 @@ keysSet m = fromMap (() <$ m)
 -- To obtain good performance, the smaller set must be presented as
 -- the first argument.
 --
--- ==== __Examples__
---
 -- >>> union (fromList [1,2]) (fromList [2,3])
 -- fromList [1,2,3]
 union :: (Eq a, Hashable a) => HashSet a -> HashSet a -> HashSet a
@@ -303,48 +316,79 @@ unions = List.foldl' union empty
 {-# INLINE unions #-}
 
 -- | /O(1)/ Return 'True' if this set is empty, 'False' otherwise.
+--
+-- >>> HashSet.null HashSet.empty
+-- True
+-- >>> HashSet.null (HashSet.singleton 1)
+-- False
 null :: HashSet a -> Bool
 null = H.null . asMap
 {-# INLINE null #-}
 
 -- | /O(n)/ Return the number of elements in this set.
+--
+-- >>> HashSet.size HashSet.empty
+-- 0
+-- >>> HashSet.size (HashSet.fromList [1,2,3])
+-- 3
 size :: HashSet a -> Int
 size = H.size . asMap
 {-# INLINE size #-}
 
 -- | /O(log n)/ Return 'True' if the given value is present in this
 -- set, 'False' otherwise.
+--
+-- >>> HashSet.member 1 (Hashset.fromList [1,2,3])
+-- True
+-- >>> HashSet.member 1 (Hashset.fromList [4,5,6])
+-- False
 member :: (Eq a, Hashable a) => a -> HashSet a -> Bool
 member a s = case H.lookup a (asMap s) of
                Just _ -> True
                _      -> False
 {-# INLINABLE member #-}
 
 -- | /O(log n)/ Add the specified value to this set.
+--
+-- >>> HashSet.insert 1 HashSet.empty
+-- fromList [1]
 insert :: (Eq a, Hashable a) => a -> HashSet a -> HashSet a
 insert a = HashSet . H.insert a () . asMap
 {-# INLINABLE insert #-}
 
--- | /O(log n)/ Remove the specified value from this set if
--- present.
+-- | /O(log n)/ Remove the specified value from this set if present.
+--
+-- >>> HashSet.delete 1 (HashSet.fromList [1,2,3])
+-- fromList [2,3]
+-- >>> HashSet.delete 1 (HashSet.fromList [4,5,6])
+-- fromList [4,5,6]
 delete :: (Eq a, Hashable a) => a -> HashSet a -> HashSet a
 delete a = HashSet . H.delete a . asMap
 {-# INLINABLE delete #-}
 
 -- | /O(n)/ Transform this set by applying a function to every value.
 -- The resulting set may be smaller than the source.
+--
+-- >>> HashSet.map show (HashSet.fromList [1,2,3])
+-- HashSet.fromList ["1","2","3"]
 map :: (Hashable b, Eq b) => (a -> b) -> HashSet a -> HashSet b
 map f = fromList . List.map f . toList
 {-# INLINE map #-}
 
 -- | /O(n)/ Difference of two sets. Return elements of the first set
 -- not existing in the second.
+--
+-- >>> HashSet.difference (HashSet.fromList [1,2,3]) (HashSet.fromList [2,3,4])
+-- fromList [1]
 difference :: (Eq a, Hashable a) => HashSet a -> HashSet a -> HashSet a
 difference (HashSet a) (HashSet b) = HashSet (H.difference a b)
 {-# INLINABLE difference #-}
 
 -- | /O(n)/ Intersection of two sets. Return elements present in both
 -- the first set and the second.
+--
+-- >>> HashSet.intersection (HashSet.fromList [1,2,3]) (HashSet.fromList [2,3,4])
+-- fromList [2,3]
 intersection :: (Eq a, Hashable a) => HashSet a -> HashSet a -> HashSet a
 intersection (HashSet a) (HashSet b) = HashSet (H.intersection a b)
 {-# INLINABLE intersection #-}