Safe Haskell | None |
---|---|
Language | Haskell2010 |
This module allows for incremental decoding and encoding of CSV data. This is useful if you e.g. want to interleave I/O with parsing or if you want finer grained control over how you deal with type conversion errors.
Decoding example:
main :: IO () main = withFile "salaries.csv" ReadMode $ \ csvFile -> do let loop !_ (Fail _ errMsg) = putStrLn errMsg >> exitFailure loop acc (Many rs k) = loop (acc + sumSalaries rs) =<< feed k loop acc (Done rs) = putStrLn $ "Total salaries: " ++ show (sumSalaries rs + acc) feed k = do isEof <- hIsEOF csvFile if isEof then return $ k B.empty else k `fmap` B.hGetSome csvFile 4096 loop 0 (decode NoHeader) where sumSalaries rs = sum [salary | Right (_ :: String, salary :: Int) <- rs]
Encoding example:
data Person = Person { name :: !String, salary :: !Int } deriving Generic instance FromNamedRecord Person instance ToNamedRecord Person instance DefaultOrdered Person persons :: [Person] persons = [Person "John" 50000, Person "Jane" 60000] main :: IO () main = putStrLn $ encodeDefaultOrderedByName (go persons) where go (x:xs) = encodeNamedRecord x <> go xs
- data HeaderParser a
- = FailH !ByteString String
- | PartialH (ByteString -> HeaderParser a)
- | DoneH !Header a
- decodeHeader :: HeaderParser ByteString
- decodeHeaderWith :: DecodeOptions -> HeaderParser ByteString
- data Parser a
- data HasHeader
- decode :: FromRecord a => HasHeader -> Parser a
- decodeWith :: FromRecord a => DecodeOptions -> HasHeader -> Parser a
- decodeByName :: FromNamedRecord a => HeaderParser (Parser a)
- decodeByNameWith :: FromNamedRecord a => DecodeOptions -> HeaderParser (Parser a)
- encode :: ToRecord a => Builder a -> ByteString
- encodeWith :: ToRecord a => EncodeOptions -> Builder a -> ByteString
- encodeRecord :: ToRecord a => a -> Builder a
- data Builder a
- encodeByName :: ToNamedRecord a => Header -> NamedBuilder a -> ByteString
- encodeDefaultOrderedByName :: (DefaultOrdered a, ToNamedRecord a) => NamedBuilder a -> ByteString
- encodeByNameWith :: ToNamedRecord a => EncodeOptions -> Header -> NamedBuilder a -> ByteString
- encodeDefaultOrderedByNameWith :: forall a. (DefaultOrdered a, ToNamedRecord a) => EncodeOptions -> NamedBuilder a -> ByteString
- encodeNamedRecord :: ToNamedRecord a => a -> NamedBuilder a
- data NamedBuilder a
Decoding
data HeaderParser a
An incremental parser that when fed data eventually returns a
parsed Header
, or an error.
FailH !ByteString String | The input data was malformed. The first field contains any unconsumed input and second field contains information about the parse error. |
PartialH (ByteString -> HeaderParser a) | The parser needs more input data before it can produce a
result. Use an |
DoneH !Header a | The parse succeeded and produced the given |
Functor HeaderParser | |
Show a => Show (HeaderParser a) |
decodeHeader :: HeaderParser ByteString
Parse a CSV header in an incremental fashion. When done, the
HeaderParser
returns any unconsumed input in the second field of
the DoneH
constructor.
decodeHeaderWith :: DecodeOptions -> HeaderParser ByteString
Like decodeHeader
, but lets you customize how the CSV data is
parsed.
Just like in the case of non-incremental decoding, there are two ways to convert CSV records to and from and user-defined data types: index-based conversion and name-based conversion.
data Parser a
An incremental parser that when fed data eventually produces some parsed records, converted to the desired type, or an error in case of malformed input data.
Fail !ByteString String | The input data was malformed. The first field contains any unconsumed input and second field contains information about the parse error. |
Many [Either String a] (ByteString -> Parser a) | The parser parsed and converted zero or more records. Any
records that failed type conversion are returned as |
Done [Either String a] | The parser parsed and converted some records. Any records
that failed type conversion are returned as |
Index-based record conversion
See documentation on index-based conversion in Data.Csv for more information.
data HasHeader
Is the CSV data preceded by a header?
:: FromRecord a | |
=> HasHeader | Data contains header that should be skipped |
-> Parser a |
Efficiently deserialize CSV in an incremental fashion. Equivalent
to
.decodeWith
defaultDecodeOptions
:: FromRecord a | |
=> DecodeOptions | Decoding options |
-> HasHeader | Data contains header that should be skipped |
-> Parser 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 :: FromNamedRecord a => HeaderParser (Parser a)
Efficiently deserialize CSV in an incremental fashion. The data
is assumed to be preceeded by a header. Returns a HeaderParser
that when done produces a Parser
for parsing the actual records.
Equivalent to
.decodeByNameWith
defaultDecodeOptions
:: FromNamedRecord a | |
=> DecodeOptions | Decoding options |
-> HeaderParser (Parser a) |
Like decodeByName
, but lets you customize how the CSV data is
parsed.
Encoding
Index-based record conversion
See documentation on index-based conversion in Data.Csv for more information.
encode :: ToRecord a => Builder a -> ByteString
Efficiently serialize records in an incremental
fashion. Equivalent to
.encodeWith
defaultEncodeOptions
encodeWith :: ToRecord a => EncodeOptions -> Builder a -> ByteString
Like encode
, but lets you customize how the CSV data is
encoded.
encodeRecord :: ToRecord a => a -> Builder a
Encode a single record.
data Builder a
Name-based record conversion
See documentation on name-based conversion in Data.Csv for more information.
encodeByName :: ToNamedRecord a => Header -> NamedBuilder a -> ByteString
Efficiently serialize named records in an incremental fashion,
including the leading header. Equivalent to
. The header is written before any records
and dictates the field order.encodeWith
defaultEncodeOptions
encodeDefaultOrderedByName :: (DefaultOrdered a, ToNamedRecord a) => NamedBuilder a -> ByteString
Like encodeByName
, but header and field order is dictated by
the headerOrder
method.
encodeByNameWith :: ToNamedRecord a => EncodeOptions -> Header -> NamedBuilder a -> ByteString
Like encodeByName
, but lets you customize how the CSV data is
encoded.
encodeDefaultOrderedByNameWith :: forall a. (DefaultOrdered a, ToNamedRecord a) => EncodeOptions -> NamedBuilder a -> ByteString
Like encodeDefaultOrderedByName
, but lets you customize how the
CSV data is encoded.
encodeNamedRecord :: ToNamedRecord a => a -> NamedBuilder a
Encode a single named record.
data NamedBuilder a
A builder for building the CSV data incrementally. Just like the
ByteString
builder, this builder should be used in a
right-associative, foldr
style. Using <>
to compose builders in
a left-associative, foldl'
style makes the building not be
incremental.
Monoid (NamedBuilder a) |