Modulecassava-0.5.3.2Haskell2010

Data.Csv.Streaming

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.

2 types
4 values

Packagecassava-0.5.3.2
Exports6
LanguageHaskell2010
LicenceBSD-3-Clause
SourceStreaming.hs

Usage example

0 declarations

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

1 declaration

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

datadata Records a

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.

Instances6Functor, Foldable, Traversable, Eq, Show, NFData

Functor RecordsDefined in cassava-0.5.3.2 · Data.Csv.Streaming
Foldable RecordsDefined in cassava-0.5.3.2 · Data.Csv.Streaming
Skips records that failed to convert.
Traversable RecordsDefined in cassava-0.5.3.2 · Data.Csv.Streaming
Eq a => Eq (Records a)Defined in cassava-0.5.3.2 · Data.Csv.Streaming
Show a => Show (Records a)Defined in cassava-0.5.3.2 · Data.Csv.Streaming
NFData a => NFData (Records a)Defined in cassava-0.5.3.2 · Data.Csv.Streaming

Decoding records

0 declarations

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.

datadata HasHeader

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

valuedecode

:: 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.

valuedecodeWith

:: 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.

valuedecodeByName

:: 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.

valuedecodeByNameWith

:: 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.