couch-hs-0.1.6: A CouchDB view server for Haskell.




Map Functions

type ReduceSignature a = [Value] -> [Value] -> Bool -> ViewReduce aSource

The type of your reduce functions as they are stored in CouchDB. The trivial example:

 \keys values rereduce -> return Null

data ViewReduce a Source

The monad within which a reduce computation takes place. This is a transformation of the Parser monad, which is accessible through the MonadParser typeclass.

JSON Parsing

JSON parsers lifted into our view monads. This also exports one or two useful symbols from Data.Aeson.Types.

class Monad m => MonadParser m whereSource

Like MonadIO, but for Parser. This allows JSON parsing operations to be lifted into our various view monads.


liftParser :: Parser a -> m aSource

parseJSON :: (MonadParser m, FromJSON a) => Value -> m aSource

Attempts to parse a JSON value into a given type. This is typically used with a type annotation to indicate the target type. If the value can not be parsed into that type, the entire computation will fail.

parseJSONList :: (MonadParser m, FromJSON a) => [Value] -> m [a]Source

Applies parseJSON to a list of values. This is commonly used with the reduce function arguments.

(.:) :: (MonadParser m, FromJSON a) => Object -> Text -> m aSource

Parses a required field of an object. If the field is not present, or the value can not be parsed into the target type, the computation will fail.

(.:?) :: (MonadParser m, FromJSON a) => Object -> Text -> m (Maybe a)Source

Parses an optional field of an object. This will not halt the computation on failure.

(.=) :: ToJSON a => Text -> a -> Pair

Construct a Pair from a key and a value.

object :: [Pair] -> Value

Create a Value from a list of name/value Pairs. If duplicate keys arise, earlier keys and their associated values win.

data Value

A JSON value represented as a Haskell value.

ViewReduce Monads

logMsg :: String -> ViewReduce ()Source

Send a log message to the CouchDB server. Note that log messages are only sent if the computation succeeds. If you want to log a message in the event of a failure, look at Alternative.