| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Text.Toml.Types
Documentation
emptyTable :: Table #
Contruct an empty Table.
Constructors
| VTable !Table | |
| VTArray !VTArray | |
| VString !Text | |
| VInteger !Int64 | |
| VFloat !Double | |
| VBoolean !Bool | |
| VDatetime !UTCTime | |
| VArray !VArray |
Instances
| Eq Node # | |
| Show Node # | |
| ToJSON Node # |
|
| ToBsJSON Node # |
As seen in this function, BurntSushi's JSON encoding explicitly specifies the types of the values. |
data Explicitness #
To mark whether or not a Table has been explicitly defined.
See: https://github.com/toml-lang/toml/issues/376
Instances
isExplicit :: Explicitness -> Bool #
Convenience function to get a boolean value.
A type that can be converted to JSON.
Instances in general must specify toJSON and should (but don't need
to) specify toEncoding.
An example type and instance:
-- Allow ourselves to writeTextliterals. {-# LANGUAGE OverloadedStrings #-} data Coord = Coord { x :: Double, y :: Double } instanceToJSONCoord wheretoJSON(Coord x y) =object["x".=x, "y".=y]toEncoding(Coord x y) =pairs("x".=x<>"y".=y)
Instead of manually writing your ToJSON instance, there are two options
to do it automatically:
- Data.Aeson.TH provides Template Haskell functions which will derive an instance at compile time. The generated instance is optimized for your type so it will probably be more efficient than the following option.
- The compiler can provide a default generic implementation for
toJSON.
To use the second, simply add a deriving clause to your
datatype and declare a GenericToJSON instance. If you require nothing other than
defaultOptions, it is sufficient to write (and this is the only
alternative where the default toJSON implementation is sufficient):
{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance ToJSON Coord where
toEncoding = genericToEncoding defaultOptions
If on the other hand you wish to customize the generic decoding, you have to implement both methods:
customOptions =defaultOptions{fieldLabelModifier=maptoUpper} instanceToJSONCoord wheretoJSON=genericToJSONcustomOptionstoEncoding=genericToEncodingcustomOptions
Previous versions of this library only had the toJSON method. Adding
toEncoding had to reasons:
- toEncoding is more efficient for the common case that the output of
toJSONis directly serialized to aByteString. Further, expressing either method in terms of the other would be non-optimal. - The choice of defaults allows a smooth transition for existing users:
Existing instances that do not define
toEncodingstill compile and have the correct semantics. This is ensured by making the default implementation oftoEncodingusetoJSON. This produces correct results, but since it performs an intermediate conversion to aValue, it will be less efficient than directly emitting anEncoding. (this also means that specifying nothing more thaninstance ToJSON Coordwould be sufficient as a generically decoding instance, but there probably exists no good reason to not specifytoEncodingin new instances.)
Methods
Convert a Haskell value to a JSON-friendly intermediate type.
toEncoding :: a -> Encoding #
Encode a Haskell value as JSON.
The default implementation of this method creates an
intermediate Value using toJSON. This provides
source-level compatibility for people upgrading from older
versions of this library, but obviously offers no performance
advantage.
To benefit from direct encoding, you must provide an
implementation for this method. The easiest way to do so is by
having your types implement Generic using the DeriveGeneric
extension, and then have GHC generate a method body as follows.
instanceToJSONCoord wheretoEncoding=genericToEncodingdefaultOptions
toJSONList :: [a] -> Value #
toEncodingList :: [a] -> Encoding #
Instances
Type class for conversion to BurntSushi-style JSON.
BurntSushi has made a language agnostic test suite available that
this library uses. This test suit expects that values are encoded
as JSON objects with a 'type' and a value member.
Minimal complete definition
Instances
| ToBsJSON Node # |
As seen in this function, BurntSushi's JSON encoding explicitly specifies the types of the values. |
| ToBsJSON a => ToBsJSON (Vector a) # | |
| ToBsJSON v => ToBsJSON (HashMap Text v) # | Provide a |