cassava-0.4.4.0: A CSV parsing and encoding library

Safe Haskell | None
Language | Haskell98

Data.Csv

Contents

- Usage examples
  - Encoding and decoding custom data types
    - Index-based record conversion
    - Name-based record conversion
- Treating CSV data as opaque byte strings
- Custom type conversions
  - Dealing with bad data
- Encoding and decoding
  - Encoding and decoding options
- Core CSV types
- Type conversion
  - Index-based record conversion
  - Name-based record conversion
  - Field conversion

Description

This module implements encoding and decoding of CSV data. The implementation is RFC 4180 compliant, with the following extensions:

- Empty lines are ignored.
- Non-escaped fields may contain any characters except double-quotes, commas, carriage returns, and newlines.
- Escaped fields may contain any characters (but double-quotes need to be escaped).

Synopsis

- data HasHeader
  - = HasHeader
  - | NoHeader
- decode :: FromRecord a => HasHeader -> ByteString -> Either String (Vector a)
- decodeByName :: FromNamedRecord a => ByteString -> Either String (Header, Vector a)
- data Quoting
  - = QuoteNone
  - | QuoteMinimal
  - | QuoteAll
- encode :: ToRecord a => [a] -> ByteString
- encodeByName :: ToNamedRecord a => Header -> [a] -> ByteString
- encodeDefaultOrderedByName :: (DefaultOrdered a, ToNamedRecord a) => [a] -> ByteString
- class DefaultOrdered a where
  - headerOrder :: a -> Header
- data DecodeOptions = DecodeOptions {
  - decDelimiter :: !Word8
  }
- defaultDecodeOptions :: DecodeOptions
- decodeWith :: FromRecord a => DecodeOptions -> HasHeader -> ByteString -> Either String (Vector a)
- decodeByNameWith :: FromNamedRecord a => DecodeOptions -> ByteString -> Either String (Header, Vector a)
- data EncodeOptions = EncodeOptions {
  - encDelimiter :: !Word8
  - encUseCrLf :: !Bool
  - encIncludeHeader :: !Bool
  - encQuoting :: !Quoting
  }
- defaultEncodeOptions :: EncodeOptions
- encodeWith :: ToRecord a => EncodeOptions -> [a] -> ByteString
- encodeByNameWith :: ToNamedRecord a => EncodeOptions -> Header -> [a] -> ByteString
- encodeDefaultOrderedByNameWith :: forall a. (DefaultOrdered a, ToNamedRecord a) => EncodeOptions -> [a] -> ByteString
- type Csv = Vector Record
- type Record = Vector Field
- type Field = ByteString
- type Header = Vector Name
- type Name = ByteString
- type NamedRecord = HashMap ByteString ByteString
- class FromRecord a where
  - parseRecord :: Record -> Parser a
- data Parser a
- runParser :: Parser a -> Either String a
- index :: FromField a => Record -> Int -> Parser a
- (.!) :: FromField a => Record -> Int -> Parser a
- unsafeIndex :: FromField a => Record -> Int -> Parser a
- class ToRecord a where
  - toRecord :: a -> Record
- record :: [ByteString] -> Record
- newtype Only a = Only {
  - fromOnly :: a
  }
- class FromNamedRecord a where
  - parseNamedRecord :: NamedRecord -> Parser a
- lookup :: FromField a => NamedRecord -> ByteString -> Parser a
- (.:) :: FromField a => NamedRecord -> ByteString -> Parser a
- class ToNamedRecord a where
  - toNamedRecord :: a -> NamedRecord
- namedRecord :: [(ByteString, ByteString)] -> NamedRecord
- namedField :: ToField a => ByteString -> a -> (ByteString, ByteString)
- (.=) :: ToField a => ByteString -> a -> (ByteString, ByteString)
- header :: [ByteString] -> Header
- class FromField a where
  - parseField :: Field -> Parser a
- class ToField a where
  - toField :: a -> Field

# Usage examples

Encoding standard Haskell types:

    >>> encode [("John" :: Text, 27), ("Jane", 28)]
    "John,27\r\nJane,28\r\n"

Since string literals are overloaded we have to supply a type signature as the compiler couldn't deduce which string type (i.e. `String` or `Text`) we want to use. In most cases type inference will infer the type from the context and you can omit type signatures.

Decoding standard Haskell types:

    >>> decode NoHeader "John,27\r\nJane,28\r\n" :: Either String (Vector (Text, Int))
    Right [("John",27),("Jane",28)]

We pass `NoHeader` as the first argument to indicate that the CSV input data isn't preceded by a header.

In practice, the return type of `decode` rarely needs to be given, as it can often be inferred from the context.

## Encoding and decoding custom data types

To encode and decode your own data types you need to defined instances of either `ToRecord` and `FromRecord` or `ToNamedRecord` and `FromNamedRecord`. The former is used for encoding/decoding using the column index and the latter using column name.

There are two ways to to define these instances, either by manually defining them or by using GHC generics to derive them automatically.

### Index-based record conversion

Derived:

    {-# LANGUAGE DeriveGeneric #-}

    data Person = Person { name :: !Text , salary :: !Int }
        deriving Generic

    instance FromRecord Person
    instance ToRecord Person

Manually defined:

    data Person = Person { name :: !Text , salary :: !Int }

    instance FromRecord Person where
        parseRecord v
            | length v == 2 = Person <$> v .! 0 <*> v .! 1
            | otherwise     = mzero
    instance ToRecord Person where
        toRecord (Person name age) = record [
            toField name, toField age]

We can now use e.g. `encode` and `decode` to encode and decode our data type.

Encoding:

    >>> encode [Person ("John" :: Text) 27]
    "John,27\r\n"

Decoding:

    >>> decode NoHeader "John,27\r\n" :: Either String (Vector Person)
    Right (["name","salary"],[Person {name = "John", salary = 27}])

### Name-based record conversion

Derived:

    {-# LANGUAGE DeriveGeneric #-}

    data Person = Person { name :: !Text , salary :: !Int }
        deriving Generic

    instance FromNamedRecord Person
    instance ToNamedRecord Person
    instance DefaultOrdered Person

Manually defined:

    data Person = Person { name :: !Text , salary :: !Int }

    instance FromNamedRecord Person where
        parseNamedRecord m = Person <$> m .: "name" <*> m .: "salary"
    instance ToNamedRecord Person
        toNamedRecord (Person name salary) = namedRecord [
            "name" .= name, "salary" .= salary]
    instance DefaultOrdered Person
        where headerOrder = header ["name", "salary"]

We can now use e.g. `encodeDefaultOrderedByName` (or `encodeByName` with an explicit header order) and `decodeByName` to encode and decode our data type.

Encoding:

    >>> encodeDefaultOrderedByName [Person ("John" :: Text) 27]
    "name,salary\r\nJohn,27\r\n"

Decoding:

    >>> decodeByName "name,salary\r\nJohn,27\r\n" :: Either String (Header, Vector Person)
    Right (["name","salary"],[Person {name = "John", salary = 27}])

# Treating CSV data as opaque byte strings

Sometimes you might want to work with a CSV file which contents is unknown to you. For example, you might want remove the second column of a file without knowing anything about its content. To parse a CSV file to a generic representation, just convert each record to a ``Vector` `ByteString`` value, like so:

    >>> decode NoHeader "John,27\r\nJane,28\r\n" :: Either String (Vector (Vector ByteString))
    Right [["John","27"],["Jane","28"]]

As the example output above shows, all the fields are returned as uninterpreted `ByteString` values.

# Custom type conversions

Most of the time the existing `FromField` and `ToField` instances do what you want. However, if you need to parse a different format (e.g. hex) but use a type (e.g. `Int`) for which there's already a `FromField` instance, you need to use a `newtype`. Example:

    newtype Hex = Hex Int

    parseHex :: ByteString -> Parser Int
    parseHex = ...

    instance FromField Hex where
        parseField s = Hex <$> parseHex s

Other than giving an explicit type signature, you can pattern match on the `newtype` constructor to indicate which type conversion you want to have the library use:

    case decode NoHeader "0xff,0xaa\r\n0x11,0x22\r\n" of
        Left err -> putStrLn err
        Right v  -> forM_ v $ \ (Hex val1, Hex val2) ->
            print (val1, val2)

If a field might be in one several different formats, you can use a newtype to normalize the result:

    newtype HexOrDecimal = HexOrDecimal Int

    instance FromField DefaultToZero where
        parseField s = case runParser (parseField s :: Parser Hex) of
            Left err -> HexOrDecimal <$> parseField s  -- Uses Int instance
            Right n  -> pure $ HexOrDecimal n

You can use the unit type, `()`, to ignore a column. The `parseField` method for `()` doesn't look at the `Field` and thus always decodes successfully. Note that it lacks a corresponding `ToField` instance. Example:

    case decode NoHeader "foo,1\r\nbar,22" of
        Left  err -> putStrLn err
        Right v   -> forM_ v $ \ ((), i) -> print (i :: Int)

## Dealing with bad data

If your input might contain invalid fields, you can write a custom `FromField` instance to deal with them. Example:

    newtype DefaultToZero = DefaultToZero Int

    instance FromField DefaultToZero where
        parseField s = case runParser (parseField s) of
            Left err -> pure $ DefaultToZero 0
            Right n  -> pure $ DefaultToZero n

# Encoding and decoding

Encoding and decoding is a two step process. To encode a value, it is first converted to a generic representation, using either `ToRecord` or `ToNamedRecord`. The generic representation is then encoded as CSV data. To decode a value the process is reversed and either `FromRecord` or `FromNamedRecord` is used instead. Both these steps are combined in the `encode` and `decode` functions.

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
-> Either String (Vector a) |

Efficiently deserialize CSV records from a lazy `ByteString`. If this fails due to incomplete or invalid input, ``Left` msg` is returned. Equivalent to ``decodeWith` `defaultDecodeOptions``.

decodeByName Source

Arguments

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

Efficiently deserialize CSV records from a lazy `ByteString`. If this fails due to incomplete or invalid input, ``Left` msg` is returned. The data is assumed to be preceeded by a header. Equivalent to ``decodeByNameWith` `defaultDecodeOptions``.

data Quoting Source

Should quoting be applied to fields, and at which level

Constructors

QuoteNone | No quotes
QuoteMinimal | Quotes according to RFC 4180
QuoteAll | Always quote

Instances

Eq Quoting Source |
Show Quoting Source |

encode :: ToRecord a => [a] -> ByteString Source

Efficiently serialize CSV records as a lazy `ByteString`.

encodeByName :: ToNamedRecord a => Header -> [a] -> ByteString Source

Efficiently serialize CSV records as a lazy `ByteString`. The header is written before any records and dictates the field order.

encodeDefaultOrderedByName :: (DefaultOrdered a, ToNamedRecord a) => [a] -> ByteString Source

Like `encodeByName`, but header and field order is dictated by the `header` method.

class DefaultOrdered a where Source

A type that has a default field order when converted to CSV. This class lets you specify how to get the headers to use for a record type that's an instance of `ToNamedRecord`.

To derive an instance, the type is required to only have one constructor and that constructor must have named fields (also known as selectors) for all fields.

Right: `data Foo = Foo { foo :: !Int }`

Wrong: `data Bar = Bar Int`

If you try to derive an instance using GHC generics and your type doesn't have named fields, you will get an error along the lines of:

    <interactive>:9:10:
        No instance for (DefaultOrdered (M1 S NoSelector (K1 R Char) ()))
          arising from a use of ‘Data.Csv.Conversion.$gdmheader’
        In the expression: Data.Csv.Conversion.$gdmheader
        In an equation for ‘header’:
            header = Data.Csv.Conversion.$gdmheader
        In the instance declaration for ‘DefaultOrdered Foo’

Minimal complete definition

Nothing

Methods

headerOrder :: a -> Header Source

The header order for this record. Should include the names used in the `NamedRecord` returned by `toNamedRecord`. Pass `undefined` as the argument, together with a type annotation e.g. ``headerOrder` (`undefined` :: MyRecord)`.

## Encoding and decoding options

These functions can be used to control how data is encoded and decoded. For example, they can be used to encode data in a tab-separated format instead of in a comma-separated format.

data DecodeOptions Source

Options that controls how data is decoded. These options can be used to e.g. decode tab-separated data instead of comma-separated data.

To avoid having your program stop compiling when new fields are added to `DecodeOptions`, create option records by overriding values in `defaultDecodeOptions`. Example:

    myOptions = defaultDecodeOptions {
          decDelimiter = fromIntegral (ord '\t')
        }

Constructors

DecodeOptions |

Fields

decDelimiter :: !Word8

  Field delimiter.

Instances

Eq DecodeOptions Source |
Show DecodeOptions Source |

defaultDecodeOptions :: DecodeOptions Source

Decoding options for parsing CSV files.

decodeWith Source

Arguments

:: FromRecord a |
=> DecodeOptions | Decoding options
-> HasHeader | Data contains header that should be skipped
-> ByteString | CSV data
-> Either String (Vector a) |

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

decodeByNameWith Source

Arguments

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

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

data EncodeOptions Source

Options that controls how data is encoded. These options can be used to e.g. encode data in a tab-separated format instead of in a comma-separated format.

To avoid having your program stop compiling when new fields are added to `EncodeOptions`, create option records by overriding values in `defaultEncodeOptions`. Example:

    myOptions = defaultEncodeOptions {
          encDelimiter = fromIntegral (ord '\t')
        }

N.B. The `encDelimiter` must not be the quote character (i.e. `"`) or one of the record separator characters (i.e. `\n` or `\r`).

Constructors

EncodeOptions |

Fields

encDelimiter :: !Word8

  Field delimiter.

encUseCrLf :: !Bool

  Record separator selection. `True` for CRLF (`\r\n`) and `False` for LF (`\n`).

encIncludeHeader :: !Bool

  Include a header row when encoding `ToNamedRecord` instances.

encQuoting :: !Quoting

  What kind of quoting should be applied to text fields.

Instances

Eq EncodeOptions Source |
Show EncodeOptions Source |

defaultEncodeOptions :: EncodeOptions Source

Encoding options for CSV files.

encodeWith :: ToRecord a => EncodeOptions -> [a] -> ByteString Source

Like `encode`, but lets you customize how the CSV data is encoded.

encodeByNameWith :: ToNamedRecord a => EncodeOptions -> Header -> [a] -> ByteString Source

Like `encodeByName`, but lets you customize how the CSV data is encoded.

encodeDefaultOrderedByNameWith :: forall a. (DefaultOrdered a, ToNamedRecord a) => EncodeOptions -> [a] -> ByteString Source

Like `encodeDefaultOrderedByNameWith`, but lets you customize how the CSV data is encoded.

# Core CSV types

type Csv = Vector Record Source

CSV data represented as a Haskell vector of vector of bytestrings.

type Record = Vector Field Source

A record corresponds to a single line in a CSV file.

type Field = ByteString Source

A single field within a record.

type Header = Vector Name Source

The header corresponds to the first line a CSV file. Not all CSV files have a header.

type Name = ByteString Source

A header has one or more names, describing the data in the column following the name.

type NamedRecord = HashMap ByteString ByteString Source

A record corresponds to a single line in a CSV file, indexed by the column name rather than the column index.

# Type conversion

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

Index-based conversion lets you convert CSV records to and from user-defined data types by referring to a field's position (its index) in the record. The first column in a CSV file is given index 0, the second index 1, and so on.

class FromRecord a where Source

A type that can be converted from a single CSV record, with the possibility of failure.

When writing an instance, use `empty`, `mzero`, or `fail` to make a conversion fail, e.g. if a `Record` has the wrong number of columns.

Given this example data:

    John,56
    Jane,55

here's an example type and instance:

    data Person = Person { name :: !Text, age :: !Int }

    instance FromRecord Person where
        parseRecord v
            | length v == 2 = Person <$>
                              v .! 0 <*>
                              v .! 1
            | otherwise     = mzero

Minimal complete definition

Nothing

Methods

parseRecord :: Record -> Parser a Source

Instances

FromField a => FromRecord [a] Source |
FromField a => FromRecord (Vector a) Source |
(FromField a, Unbox a) => FromRecord (Vector a) Source |
FromField a => FromRecord (Only a) Source |
(FromField a, FromField b) => FromRecord (a, b) Source |
(FromField a, FromField b, FromField c) => FromRecord (a, b, c) Source |
(FromField a, FromField b, FromField c, FromField d) => FromRecord (a, b, c, d) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e) => FromRecord (a, b, c, d, e) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f) => FromRecord (a, b, c, d, e, f) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g) => FromRecord (a, b, c, d, e, f, g) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h) => FromRecord (a, b, c, d, e, f, g, h) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h, FromField i) => FromRecord (a, b, c, d, e, f, g, h, i) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h, FromField i, FromField j) => FromRecord (a, b, c, d, e, f, g, h, i, j) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h, FromField i, FromField j, FromField k) => FromRecord (a, b, c, d, e, f, g, h, i, j, k) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h, FromField i, FromField j, FromField k, FromField l) => FromRecord (a, b, c, d, e, f, g, h, i, j, k, l) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h, FromField i, FromField j, FromField k, FromField l, FromField m) => FromRecord (a, b, c, d, e, f, g, h, i, j, k, l, m) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h, FromField i, FromField j, FromField k, FromField l, FromField m, FromField n) => FromRecord (a, b, c, d, e, f, g, h, i, j, k, l, m, n) Source |
(FromField a, FromField b, FromField c, FromField d, FromField e, FromField f, FromField g, FromField h, FromField i, FromField j, FromField k, FromField l, FromField m, FromField n, FromField o) => FromRecord (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) Source |

data Parser a Source

Conversion of a field to a value might fail e.g. if the field is malformed. This possibility is captured by the `Parser` type, which lets you compose several field conversions together in such a way that if any of them fail, the whole record conversion fails.

Instances

Monad Parser Source |
Functor Parser Source |
Applicative Parser Source |
Alternative Parser Source |
MonadPlus Parser Source |
Monoid (Parser a) Source |

runParser :: Parser a -> Either String a Source

Run a `Parser`, returning either ``Left` errMsg` or ``Right` result`. Forces the value in the `Left` or `Right` constructors to weak head normal form.

You most likely won't need to use this function directly, but it's included for completeness.

index :: FromField a => Record -> Int -> Parser a Source

Retrieve the nth field in the given record. The result is `empty` if the value cannot be converted to the desired type. Raises an exception if the index is out of bounds.

`index` is a simple convenience function that is equivalent to ``parseField` (v `!` idx)`. If you're certain that the index is not out of bounds, using `unsafeIndex` is somewhat faster.

(.!) :: FromField a => Record -> Int -> Parser a infixl 9 Source

Alias for `index`.

unsafeIndex :: FromField a => Record -> Int -> Parser a Source

Like `index` but without bounds checking.

class ToRecord a where Source

A type that can be converted to a single CSV record.

An example type and instance:

    data Person = Person { name :: !Text, age :: !Int }

    instance ToRecord Person where
        toRecord (Person name age) = record [
            toField name, toField age]

Outputs data on this form:

    John,56
    Jane,55

Minimal complete definition

Nothing

Methods

toRecord :: a -> Record Source

Convert a value to a record.

Instances

ToField a => ToRecord [a] Source |
ToField a => ToRecord (Vector a) Source |
(ToField a, Unbox a) => ToRecord (Vector a) Source |
ToField a => ToRecord (Only a) Source |
(ToField a, ToField b) => ToRecord (a, b) Source |
(ToField a, ToField b, ToField c) => ToRecord (a, b, c) Source |
(ToField a, ToField b, ToField c, ToField d) => ToRecord (a, b, c, d) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e) => ToRecord (a, b, c, d, e) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f) => ToRecord (a, b, c, d, e, f) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g) => ToRecord (a, b, c, d, e, f, g) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h) => ToRecord (a, b, c, d, e, f, g, h) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i) => ToRecord (a, b, c, d, e, f, g, h, i) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j) => ToRecord (a, b, c, d, e, f, g, h, i, j) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j, ToField k) => ToRecord (a, b, c, d, e, f, g, h, i, j, k) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j, ToField k, ToField l) => ToRecord (a, b, c, d, e, f, g, h, i, j, k, l) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j, ToField k, ToField l, ToField m) => ToRecord (a, b, c, d, e, f, g, h, i, j, k, l, m) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j, ToField k, ToField l, ToField m, ToField n) => ToRecord (a, b, c, d, e, f, g, h, i, j, k, l, m, n) Source |
(ToField a, ToField b, ToField c, ToField d, ToField e, ToField f, ToField g, ToField h, ToField i, ToField j, ToField k, ToField l, ToField m, ToField n, ToField o) => ToRecord (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) Source |

record :: [ByteString] -> Record Source

Construct a record from a list of `ByteString`s. Use `toField` to convert values to `ByteString`s for use with `record`.

newtype Only a Source

Haskell lacks a single-element tuple type, so if you CSV data with just one column you can use the `Only` type to represent a single-column result.

Constructors

Only |

Fields

fromOnly :: a

Instances

Eq a => Eq (Only a) Source |
Ord a => Ord (Only a) Source |
Read a => Read (Only a) Source |
Show a => Show (Only a) Source |
ToField a => ToRecord (Only a) Source |
FromField a => FromRecord (Only a) Source |

## Name-based record conversion

Name-based conversion lets you convert CSV records to and from user-defined data types by referring to a field's name. The names of the fields are defined by the first line in the file, also known as the header. Name-based conversion is more robust to changes in the file structure e.g. to reording or addition of columns, but can be a bit slower.

class FromNamedRecord a where Source

A type that can be converted from a single CSV record, with the possibility of failure.

When writing an instance, use `empty`, `mzero`, or `fail` to make a conversion fail, e.g. if a `Record` has the wrong number of columns.

Given this example data:

    name,age
    John,56
    Jane,55

here's an example type and instance:

    {-# LANGUAGE OverloadedStrings #-}

    data Person = Person { name :: !Text, age :: !Int }

    instance FromNamedRecord Person where
        parseNamedRecord m = Person <$>
                             m .: "name" <*>
                             m .: "age"

Note the use of the `OverloadedStrings` language extension which enables `ByteString` values to be written as string literals.

Minimal complete definition

Nothing

Methods

parseNamedRecord :: NamedRecord -> Parser a Source

Instances

(FromField a, FromField b, Ord a) => FromNamedRecord (Map a b) Source |
(Eq a, FromField a, FromField b, Hashable a) => FromNamedRecord (HashMap a b) Source |

lookup :: FromField a => NamedRecord -> ByteString -> Parser a Source

Retrieve a field in the given record by name. The result is `empty` if the field is missing or if the value cannot be converted to the desired type.

(.:) :: FromField a => NamedRecord -> ByteString -> Parser a Source

Alias for `lookup`.

class ToNamedRecord a where Source

A type that can be converted to a single CSV record.

An example type and instance:

    data Person = Person { name :: !Text, age :: !Int }

    instance ToNamedRecord Person where
        toNamedRecord (Person name age) = namedRecord [
            "name" .= name, "age" .= age]

Minimal complete definition

Nothing

Methods

toNamedRecord :: a -> NamedRecord Source

Convert a value to a named record.

Instances

(ToField a, ToField b, Ord a) => ToNamedRecord (Map a b) Source |
(Eq a, ToField a, ToField b, Hashable a) => ToNamedRecord (HashMap a b) Source |

namedRecord :: [(ByteString, ByteString)] -> NamedRecord Source

Construct a named record from a list of name-value `ByteString` pairs. Use `.=` to construct such a pair from a name and a value.

namedField :: ToField a => ByteString -> a -> (ByteString, ByteString) Source

Construct a pair from a name and a value. For use with `namedRecord`.

(.=) :: ToField a => ByteString -> a -> (ByteString, ByteString) Source

Alias for `namedField`.

header :: [ByteString] -> Header Source

Construct a header from a list of `ByteString`s.

## Field conversion

The `FromField` and `ToField` classes define how to convert between `Field`s and values you care about (e.g. `Int`s). Most of the time you don't need to write your own instances as the standard ones cover most use cases.

class FromField a where Source

A type that can be converted from a single CSV field, with the possibility of failure.

When writing an instance, use `empty`, `mzero`, or `fail` to make a conversion fail, e.g. if a `Field` can't be converted to the given type.

Example type and instance:

    {-# LANGUAGE OverloadedStrings #-}

    data Color = Red | Green | Blue

    instance FromField Color where
        parseField s
            | s == "R"  = pure Red
            | s == "G"  = pure Green
            | s == "B"  = pure Blue
            | otherwise = mzero

Methods

parseField :: Field -> Parser a Source

Instances

FromField Char Source | Assumes UTF-8 encoding.
FromField Double Source | Accepts same syntax as `rational`. Ignores whitespace.
FromField Float Source | Accepts same syntax as `rational`. Ignores whitespace.
FromField Int Source | Accepts a signed decimal number. Ignores whitespace.
FromField Int8 Source | Accepts a signed decimal number. Ignores whitespace.
FromField Int16 Source | Accepts a signed decimal number. Ignores whitespace.
FromField Int32 Source | Accepts a signed decimal number. Ignores whitespace.
FromField Int64 Source | Accepts a signed decimal number. Ignores whitespace.
FromField Integer Source | Accepts a signed decimal number. Ignores whitespace.
FromField Word Source | Accepts an unsigned decimal number. Ignores whitespace.
FromField Word8 Source | Accepts an unsigned decimal number. Ignores whitespace.
FromField Word16 Source | Accepts an unsigned decimal number. Ignores whitespace.
FromField Word32 Source | Accepts an unsigned decimal number. Ignores whitespace.
FromField Word64 Source | Accepts an unsigned decimal number. Ignores whitespace.
FromField () Source | Ignores the `Field`. Always succeeds.
FromField ByteString Source |
FromField ByteString Source |
FromField Text Source | Assumes UTF-8 encoding. Fails on invalid byte sequences.
FromField Text Source | Assumes UTF-8 encoding. Fails on invalid byte sequences.
FromField ShortByteString Source |
FromField [Char] Source | Assumes UTF-8 encoding. Fails on invalid byte sequences.
FromField a => FromField (Maybe a) Source | `Nothing` if the `Field` is `empty`, `Just` otherwise.
FromField a => FromField (Either Field a) Source | ``Left` field` if conversion failed, `Right` otherwise.

class ToField a where Source

A type that can be converted to a single CSV field.

Example type and instance:

    {-# LANGUAGE OverloadedStrings #-}

    data Color = Red | Green | Blue

    instance ToField Color where
        toField Red   = "R"
        toField Green = "G"
        toField Blue  = "B"

Methods

toField :: a -> Field Source

Instances

ToField Char Source | Uses UTF-8 encoding.
ToField Double Source | Uses decimal notation or scientific notation, depending on the number.
ToField Float Source | Uses decimal notation or scientific notation, depending on the number.
ToField Int Source | Uses decimal encoding with optional sign.
ToField Int8 Source | Uses decimal encoding with optional sign.
ToField Int16 Source | Uses decimal encoding with optional sign.
ToField Int32 Source | Uses decimal encoding with optional sign.
ToField Int64 Source | Uses decimal encoding with optional sign.
ToField Integer Source | Uses decimal encoding with optional sign.
ToField Word Source | Uses decimal encoding.
ToField Word8 Source | Uses decimal encoding.
ToField Word16 Source | Uses decimal encoding.
ToField Word32 Source | Uses decimal encoding.
ToField Word64 Source | Uses decimal encoding.
ToField ByteString Source |
ToField ByteString Source |
ToField Text Source | Uses UTF-8 encoding.
ToField Text Source | Uses UTF-8 encoding.
ToField ShortByteString Source |
ToField [Char] Source | Uses UTF-8 encoding.
ToField a => ToField (Maybe a) Source | `Nothing` is encoded as an `empty` field.