| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Aws.Query.TH
Documentation
module Aws.Core
module Aws.Query
data Text :: *
A space efficient, packed, unboxed Unicode text type.
Instances
| IsList Text | |
| Eq Text | |
| Data Text | This instance preserves data abstraction at the cost of inefficiency. We omit reflection services for the sake of data abstraction. This instance was created by copying the updated behavior of
The original discussion is archived here: could we get a Data instance for Data.Text.Text? The followup discussion that changed the behavior of |
| Ord Text | |
| Read Text | |
| Show Text | |
| IsString Text | |
| ToJSON Text | |
| FromJSON Text | |
| Chunk Text | |
| Monoid Text | |
| FoldCase Text | |
| NFData Text | |
| Hashable Text | |
| QueryKeyLike Text | |
| QueryValueLike Text | |
| Semigroup Text | |
| Typeable * Text | |
| (~) * a Text => IsString (Parser a) | |
| ToJSON v => ToJSON (HashMap Text v) | |
| ToJSON v => ToJSON (Map Text v) | |
| FromJSON v => FromJSON (HashMap Text v) | |
| FromJSON v => FromJSON (Map Text v) | |
| type State Text = Buffer | |
| type ChunkElem Text = Char | |
| type Item Text = Char |
data UTCTime :: *
This is the simplest representation of UTC. It consists of the day number, and a time offset from midnight. Note that if a day has a leap second added to it, it will have 86401 seconds.
class FromJSON a
A type that can be converted from JSON, with the possibility of failure.
When writing an instance, use empty, mzero, or fail to make a
conversion fail, e.g. if an Object is missing a required key, or
the value is of the wrong type.
An example type and instance:
@{-# LANGUAGE OverloadedStrings #-}
data Coord = Coord { x :: Double, y :: Double }
instance FromJSON Coord where
parseJSON (Object v) = Coord <$>
v .: "x" <*>
v .: "y"
-- A non-Object value is of the wrong type, so use mzero to fail.
parseJSON _ = mzero
@
Note the use of the OverloadedStrings language extension which enables
Text values to be written as string literals.
Instead of manually writing your FromJSON instance, there are three 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 will probably be more efficient than the following two options:
- Data.Aeson.Generic provides a generic
fromJSONfunction that parses to any type which is an instance ofData. - If your compiler has support for the
DeriveGenericandDefaultSignatureslanguage extensions,parseJSONwill have a default generic implementation.
To use this, simply add a deriving clause to your datatype and
declare a GenericFromJSON instance for your datatype without giving a definition
for parseJSON.
For example the previous example can be simplified to just:
@{-# LANGUAGE DeriveGeneric #-}
import GHC.Generics
data Coord = Coord { x :: Double, y :: Double } deriving Generic
instance FromJSON Coord @
Note that, instead of using DefaultSignatures, it's also possible
to parameterize the generic decoding using genericParseJSON applied
to your encoding/decoding Options:
instance FromJSON Coord where
parseJSON = genericParseJSON defaultOptions
Instances