Data.Aeson.Quick

Documentation

aeson-quick is a library for terse marshalling of data to and from aeson's Value.

It works on the observation that by turning objects into tuples inside the Value, the type system can be employed to do more of the work.

For example, given the JSON:

{ "name": "bob"
, "age": 29
, "hobbies": [{"name": "tennis"}, {"name": "cooking"}]
}

You can write:

extractHobbyist :: Value -> Maybe (String, Int, [String])
extractHobbyist = (.? "{name,age,hobbies:[{name}]}")

module Data.Aeson

(.?) :: FromJSON a => Value -> Structure -> Maybe a

Extracts instances of FromJSON from a Value

This is a wrapper around extract which does the actual work.

Examples assume FromJSON Foo and FromJSON Bar.

Extract key from object:

>>> value .? "{key}" :: Maybe Foo

Extract list of objects:

>>> value .? "[{key}]" :: Maybe [Foo]

Extract with optional key:

>>> value .? "{key,opt?}" :: Maybe (Foo, Maybe Bar)

(.!) :: FromJSON a => Value -> Structure -> a

Unsafe version of .?. Returns error on failure.

extract :: FromJSON a => Structure -> Value -> Parser a

The Parser that executes a Structure against a Value to return an instance of FromJSON.

(.%) :: ToJSON a => Structure -> a -> Value

Turns data into JSON objects.

This is a wrapper around build which does the actual work.

Build a simple Value:

>>> encode $ "{a}" .% True
{\"a\": True}

Build a complex Value:

>>> encode $ "[{a}]" '.%' [True, False]
"[{\"a\":true},{\"a\":false}]"

build :: ToJSON a => Structure -> Value -> a -> Value

Executes a Structure against provided data to update a Value.

Note: Still has undefined behaviours, not at all stable.

data Structure

Constructors

Obj [(Text, Bool, Structure)]

Arr Structure

Val

Instances

Eq Structure

Defined in Data.Aeson.Quick

Methods

(==) :: Structure -> Structure -> Bool

(/=) :: Structure -> Structure -> Bool

Ord Structure

Defined in Data.Aeson.Quick

Methods

compare :: Structure -> Structure -> Ordering

(<) :: Structure -> Structure -> Bool

(<=) :: Structure -> Structure -> Bool

(>) :: Structure -> Structure -> Bool

(>=) :: Structure -> Structure -> Bool

max :: Structure -> Structure -> Structure

min :: Structure -> Structure -> Structure

Show Structure

Defined in Data.Aeson.Quick

Methods

showsPrec :: Int -> Structure -> ShowS

show :: Structure -> String

showList :: [Structure] -> ShowS

IsString Structure

Defined in Data.Aeson.Quick

Methods

fromString :: String -> Structure

Generic Structure

Defined in Data.Aeson.Quick

Associated Types

type Rep Structure :: * -> *

Methods

from :: Structure -> Rep Structure x

to :: Rep Structure x -> Structure

NFData Structure

Defined in Data.Aeson.Quick

Methods

rnf :: Structure -> ()

type Rep Structure

Defined in Data.Aeson.Quick

type Rep Structure = D1 (MetaData "Structure" "Data.Aeson.Quick" "aeson-quick-0.1.2.1-DSsrtXgxAed6e1JH1TOst6" False) (C1 (MetaCons "Obj" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 [(Text, Bool, Structure)])) :+: (C1 (MetaCons "Arr" PrefixI False) (S1 (MetaSel (Nothing :: Maybe Symbol) NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 Structure)) :+: C1 (MetaCons "Val" PrefixI False) (U1 :: * -> *)))

parseStructure :: Text -> Either String Structure

Parse a structure, can fail