Prolude.Csv

Csv re-exports

class ToNamedRecord a

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]

Instances

(ToField a, ToField b, Ord a) => ToNamedRecord (Map a b)

Defined in Data.Csv.Conversion

Methods

toNamedRecord :: Map a b -> NamedRecord

(Eq a, ToField a, ToField b, Hashable a) => ToNamedRecord (HashMap a b)

Defined in Data.Csv.Conversion

Methods

toNamedRecord :: HashMap a b -> NamedRecord

class DefaultOrdered a

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’

Alias types

We created type aliases for the Csv.ToField and Csv.FromField classes.

type FromCsvField = FromField

type ToCsvField = ToField

Alias functions

We created aliases for the Csv.parseField and Csv.toField functions.

parseCsvField :: FromCsvField a => Field -> Parser a

toCsvField :: ToCsvField a => a -> Field