Happstack.Data.IxSet

Assume you have a type like:

data Entry = Entry Author [Author] Updated Id Content
  newtype Updated = Updated EpochTime
  newtype Id = Id Int64
  newtype Content = Content String
  newtype Author = Author Email
  type Email = String

1. Decide what parts of your type you want indexed and make your type an instance of Indexable

instance Indexable Entry () where
    empty = ixSet 
                [ Ix (Map.empty::Map Author (Set Entry)) -- out of order
                , Ix (Map.empty::Map Id (Set Entry))
                , Ix (Map.empty::Map Updated (Set Entry))
                , Ix (Map.empty::Map Test (Set Entry))   -- bogus index
                , Ix (Map.empty::Map Word (Set Entry))   -- text index
                ]
    calcs entry = () -- words for text indexing purposes

1. Use insert, delete, updateIx, deleteIx and empty to build up an IxSet collection

entries = foldr insert empty [e1,e2,e3,e4] entries' = foldr delete entries [e1,e3] entries'' = update e4 e5 entries

1. Use the query functions below to grab data from it. e.g.

entries @< (Updated t1) @= (Author "[e-mail]")

will find all items in entries updated earlier than t1 by [e-mail].

1. Text Index

If you want to do add a text index extract the words in entry and pass them in the calc method of the Indexable class. Then if you want all entries with either word1 or word2, you change the instance to

getWords entry = let Just (Content s) =
                           gGet entry in map Word $ words s

instance Indexable Entry [Word] where
    ....
    calcs entry = getWords entry

Now you can do this query to find entries with any of the words

entries @+ [Word "word1",Word "word2"]

And if you want all entries with both:

entries @* [Word "word1",Word "word2"]

1. Find only the first author

If an Entry has multiple authors and you want to be able to query on the first author, define a FirstAuthor datatype and add it to the result of calc. calc e = (toWords e, getFirstAuthor e) and now you can do

newtype FirstAuthor = FirstAuthor Email

getFirstAuthor = let Just (Author a) = 
                          gGet Entry in FirstAuthor a

instance Indexable Entry ([Word],FirstAuthor)
    ...
    empty = ....
             Ix (Map.empty::Map FirstAuthor (Set Entry))]
    calcs entry = (getWords Entry,getFirstAuthor entry)

entries @= (FirstAuthor "[e-mail]")  -- guess what this does

Documentation

module Ix

Set type

data IxSet a

Instances

Typeable1 IxSet

(Data ctx a, Sat (ctx (IxSet a)), Sat (ctx [a]), Indexable a b, Data a, Ord a) => Data ctx (IxSet a)

(Eq a, Ord a, Typeable a) => Eq (IxSet a)

Data a => Data (IxSet a)

(Eq a, Ord a, Typeable a) => Ord (IxSet a)

(Ord a, Read a, Data a, Indexable a b) => Read (IxSet a)

(Ord a, Show a) => Show (IxSet a)

(Indexable a b, Data a, Ord a) => Monoid (IxSet a)

Version (IxSet a)

(Serialize a, Ord a, Data a, Indexable a b) => Serialize (IxSet a)

(Indexable a b, Data a, Ord a, Default a) => Default (IxSet a)

class Data b => Indexable a b | a -> b where

Indexable class defines objects that can be members of IxSet. If you don't want calculated values use Indexable a ().

Methods

empty :: IxSet a

Method empty defines what an empty IxSet for this particular type should look like. It should have all necessary indices. Use ixSet function to create the set.

calcs :: a -> b

Method calcs adds indexable values not found in the type. Those end up in indices just like other types found in objects. If you don't want any calculated values just use noCalcs.

noCalcs :: t -> ()

Function to be used for calcs in the case of an Indexable a () instance.

inferIxSet :: String -> Name -> Name -> [Name] -> Q [Dec]

Template Haskell helper function for automatically building an Indexable instance from a data type, e.g.

data Foo = Foo Int String

and

$(inferIxSet "FooDB" ''Foo 'noCalcs [''Int,''String])

will build a type synonym

type FooDB = IxSet Foo

with Int and String as indices.

WARNING: The type specified as the first index must be a type which appears in all values in the IxSet or toList and toSet will not function properly. You will be warned not to do this by runtime error. You can always use the element type itself. For example:

$(inferIxSet "FooDB" ''Foo 'noCalcs [''Foo, ''Int, ''String])

ixSet :: [Ix a] -> IxSet a

Create an IxSet using list of indices. Useful in Indexable empty method.

Changes to set

type IndexOp = forall k a. (Ord k, Ord a) => k -> a -> Map k (Set a) -> Map k (Set a)

change :: (Data a, Ord a, Data b, Indexable a b) => IndexOp -> a -> IxSet a -> IxSet a

Higher order operator for modifying IxSets. Use this when your final function should have the form a -> IxSet a -> IxSet a, e.g. insert or delete.

insert :: (Data a, Ord a, Data b, Indexable a b) => a -> IxSet a -> IxSet a

Inserts an item into the IxSet. If your data happens to have primary key this function might not be what you want. See updateIx.

delete :: (Data a, Ord a, Data b, Indexable a b) => a -> IxSet a -> IxSet a

Removes an item from the IxSet.

updateIx :: (Indexable a b, Ord a, Data a, Typeable k) => k -> a -> IxSet a -> IxSet a

Will replace the item with index k. Only works if there is at most one item with that index in the IxSet. Will not change IxSet if you have more then 1 item with given index.

deleteIx :: (Indexable a b, Ord a, Data a, Typeable k) => k -> IxSet a -> IxSet a

Will delete the item with index k. Only works if there is at most one item with that index in the IxSet. Will not change IxSet if you have more then 1 item with given index.

Creation

fromSet :: (Indexable a b, Ord a, Data a) => Set a -> IxSet a

Converts a Set to an IxSet.

fromList :: (Indexable a b, Ord a, Data a) => [a] -> IxSet a

Converts a list to an IxSet.

Conversion

toSet :: Ord a => IxSet a -> Set a

Converts an IxSet to a Set of its elements.

toList :: Ord a => IxSet a -> [a]

Converts an IxSet to its list of elements.

getOne :: Ord a => IxSet a -> Maybe a

If the IxSet is a singleton it will return the one item stored in it. If IxSet is empty or has many elements this function returns Nothing.

getOneOr :: Ord a => a -> IxSet a -> a

Like getOne with a user provided default.

Size checking

size :: Ord a => IxSet a -> Int

Returns the number of unique items in the IxSet.

null :: IxSet a -> Bool

Return True if the IxSet is empty, False otherwise.

Set operations

(&&&) :: (Ord a, Data a, Indexable a b) => IxSet a -> IxSet a -> IxSet a

An infix intersection operation.

(|||) :: (Ord a, Data a, Indexable a b) => IxSet a -> IxSet a -> IxSet a

An infix union operation.

union :: (Ord a, Data a, Indexable a b) => IxSet a -> IxSet a -> IxSet a

Takes the union of the two IxSets.

intersection :: (Ord a, Data a, Indexable a b) => IxSet a -> IxSet a -> IxSet a

Takes the intersection of the two IxSets.

Indexing

(@=) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> k -> IxSet a

Infix version of getEQ.

(@<) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> k -> IxSet a

Infix version of getLT.

(@>) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> k -> IxSet a

Infix version of getGT.

(@<=) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> k -> IxSet a

Infix version of getLTE.

(@>=) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> k -> IxSet a

Infix version of getGTE.

(@><) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> (k, k) -> IxSet a

Returns the subset with indices in the open interval (k,k).

(@>=<) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> (k, k) -> IxSet a

Returns the subset with indices in [k,k).

(@><=) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> (k, k) -> IxSet a

Returns the subset with indices in (k,k].

(@>=<=) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> (k, k) -> IxSet a

Returns the subset with indices in [k,k].

(@+) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> [k] -> IxSet a

Creates the subset that has an index in the provided list.

(@*) :: (Indexable a b, Data a, Ord a, Typeable k) => IxSet a -> [k] -> IxSet a

Creates the subset that matches all the provided indices.

getEQ :: (Indexable a b, Data a, Ord a, Typeable k) => k -> IxSet a -> IxSet a

Returns the subset with an index equal to the provided key. The set must be indexed over key type, doing otherwise results in runtime error.

getLT :: (Indexable a b, Data a, Ord a, Typeable k) => k -> IxSet a -> IxSet a

Returns the subset with an index less than the provided key. The set must be indexed over key type, doing otherwise results in runtime error.

getGT :: (Indexable a b, Data a, Ord a, Typeable k) => k -> IxSet a -> IxSet a

Returns the subset with an index greater than the provided key. The set must be indexed over key type, doing otherwise results in runtime error.

getLTE :: (Indexable a b, Data a, Ord a, Typeable k) => k -> IxSet a -> IxSet a

Returns the subset with an index less than or equal to the provided key. The set must be indexed over key type, doing otherwise results in runtime error.

getGTE :: (Indexable a b, Data a, Ord a, Typeable k) => k -> IxSet a -> IxSet a

Returns the subset with an index greater than or equal to the provided key. The set must be indexed over key type, doing otherwise results in runtime error.

getRange :: (Indexable a b, Typeable k, Ord a, Data a) => k -> k -> IxSet a -> IxSet a

Returns the subset with an index within the interval provided. The bottom of the interval is closed and the top is open, i. e. [k1;k2). The set must be indexed over key type, doing otherwise results in runtime error.

groupBy :: (Typeable k, Typeable t) => IxSet t -> [(k, [t])]

Returns lists of elements paired with the indices determined by type inference.

getOrd :: (Indexable a b, Ord a, Data a, Typeable k) => Ordering -> k -> IxSet a -> IxSet a

A function for building up selectors on IxSets. Used in the various get* functions. The set must be indexed over key type, doing otherwise results in runtime error.

Debugging and optimisation

stats :: Ord a => IxSet a -> (Int, Int, Int, Int)

Statistics about IxSet. This function returns quadruple consisting of 1. total number of elements in the set 2. number of declared indices 3. number of keys in all indices 4. number of values in all keys in all indices. This can aid you in debugging and optimisation.