Safe Haskell	None
Language	Haskell2010

Data.Csv.Streaming

Contents

Usage example
Stream representation
Decoding records
- Index-based record conversion
- Name-based record conversion

Description

This module allows for streaming decoding of CSV data. This is useful if you need to parse large amounts of input in constant space. The API also allows you to ignore type conversion errors on a per-record basis.

Synopsis

data Records a
- = Cons (Either String a) (Records a)
- | Nil (Maybe String) ByteString
data HasHeader
- = HasHeader
- | NoHeader
decode :: FromRecord a => HasHeader -> ByteString -> Records a
decodeWith :: FromRecord a => DecodeOptions -> HasHeader -> ByteString -> Records a
decodeByName :: FromNamedRecord a => ByteString -> Either String (Header, Records a)
decodeByNameWith :: FromNamedRecord a => DecodeOptions -> ByteString -> Either String (Header, Records a)

Usage example

A short usage example:

for_ (decode NoHeader "John,27\r\nJane,28\r\n") $ \ (name, age :: Int) ->
    putStrLn $ name ++ " is " ++ show age ++ " years old"

N.B. The Foldable instance, which is used above, skips records that failed to convert. If you don't want this behavior, work directly with the Cons and Nil constructors.

Stream representation

A stream of records is represented as a (lazy) list that may contain errors.

data Records a Source #

A stream of parsed records. If type conversion failed for the record, the error is returned as Left errMsg.

Constructors

Cons (Either String a) (Records a)	A record or an error message, followed by more records.
Nil (Maybe String) ByteString	End of stream, potentially due to a parse error. If a parse error occured, the first field contains the error message. The second field contains any unconsumed input.

Instances

Instances details

Functor Records Source #
Instance details Defined in Data.Csv.Streaming Methods fmap :: (a -> b) -> Records a -> Records b # (<$) :: a -> Records b -> Records a #
Foldable Records Source #	Skips records that failed to convert.
Instance details Defined in Data.Csv.Streaming Methods fold :: Monoid m => Records m -> m # foldMap :: Monoid m => (a -> m) -> Records a -> m # foldMap' :: Monoid m => (a -> m) -> Records a -> m # foldr :: (a -> b -> b) -> b -> Records a -> b # foldr' :: (a -> b -> b) -> b -> Records a -> b # foldl :: (b -> a -> b) -> b -> Records a -> b # foldl' :: (b -> a -> b) -> b -> Records a -> b # foldr1 :: (a -> a -> a) -> Records a -> a # foldl1 :: (a -> a -> a) -> Records a -> a # toList :: Records a -> [a] # null :: Records a -> Bool # length :: Records a -> Int # elem :: Eq a => a -> Records a -> Bool # maximum :: Ord a => Records a -> a # minimum :: Ord a => Records a -> a # sum :: Num a => Records a -> a # product :: Num a => Records a -> a #
Traversable Records Source #
Instance details Defined in Data.Csv.Streaming Methods traverse :: Applicative f => (a -> f b) -> Records a -> f (Records b) # sequenceA :: Applicative f => Records (f a) -> f (Records a) # mapM :: Monad m => (a -> m b) -> Records a -> m (Records b) # sequence :: Monad m => Records (m a) -> m (Records a) #
Eq a => Eq (Records a) Source #
Instance details Defined in Data.Csv.Streaming Methods (==) :: Records a -> Records a -> Bool # (/=) :: Records a -> Records a -> Bool #
Show a => Show (Records a) Source #
Instance details Defined in Data.Csv.Streaming Methods showsPrec :: Int -> Records a -> ShowS # show :: Records a -> String # showList :: [Records a] -> ShowS #
NFData a => NFData (Records a) Source #
Instance details Defined in Data.Csv.Streaming Methods rnf :: Records a -> () #

Decoding records

Just like in the case of non-streaming decoding, there are two ways to convert CSV records to and from and user-defined data types: index-based conversion and name-based conversion.

Index-based record conversion

See documentation on index-based conversion in Data.Csv for more information.

data HasHeader Source #

Is the CSV data preceded by a header?

Constructors

HasHeader	The CSV data is preceded by a header
NoHeader	The CSV data is not preceded by a header

decode Source #

Arguments

:: FromRecord a
=> HasHeader	Data contains header that should be skipped
-> ByteString	CSV data
-> Records a

Efficiently deserialize CSV records in a streaming fashion. Equivalent to decodeWith defaultDecodeOptions.

decodeWith Source #

Arguments

:: FromRecord a
=> DecodeOptions	Decoding options
-> HasHeader	Data contains header that should be skipped
-> ByteString	CSV data
-> Records a

Like decode, but lets you customize how the CSV data is parsed.

Name-based record conversion

See documentation on name-based conversion in Data.Csv for more information.

decodeByName Source #

Arguments

:: FromNamedRecord a
=> ByteString	CSV data
-> Either String (Header, Records a)

Efficiently deserialize CSV in a streaming fashion. The data is assumed to be preceded by a header. Returns Left errMsg if parsing the header fails. Equivalent to decodeByNameWith defaultDecodeOptions.

decodeByNameWith Source #

Arguments

:: FromNamedRecord a
=> DecodeOptions	Decoding options
-> ByteString	CSV data
-> Either String (Header, Records a)

Like decodeByName, but lets you customize how the CSV data is parsed.