aeson-quick

aeson-quick is a small DSL on top of aeson for casual and concise JSON construction and deconstruction.

In essence, it allows you to remove the Objects in a json Value using a simple key lookup syntax, so that the FromJSON typeclass can do the rest of the work, and it can go the other way, too.

aeson-quick structures can be defined using the fromString instance, or using the QuasiQuoter quick for compile time validation, ie: [quick|{foo}|].

Syntax

Transformations

Operation	Json Value	Quick expression	Haskell type
Parse any value	*	.	a
Key lookup	{"foo": *}	{foo}	a
Optional key	{}	{foo?}	Maybe a
Multiple keys	{"foo": *, "bar": *}	{foo,bar}	(a, b)
Nested object	{"foo": {"bar": *}}	{foo:{bar}}	b
Complex object	[{"foo": *, "bar": [*, *]}]	[{a,b:[.]}]	[(a, [c])]
Array	[*, *]	[.]	[a]
Array lookup (deconstruct only)	[*, *]	[.]1	a
Array range (deconstruct only)	[*, *]	[.]1-	[a]

Examples:

Deconstruction:

> let value = [jsonlit|{"foo": true, "bar": [0, 1], "baz": [{"foo": true}, {}, {"foo": false}]}|]

> value .! "{foo}" :: Bool
True

> value .! "{foo, bar}" :: (Bool, [Int])
(True, [0, 1])

> value .! "{baz:[{foo?}]}" :: [Maybe Bool]
[Just True, Nothing, Just False]

-- value is [1,2,3]
> value .! "[.]1" :: Int
2
> value .! "[.]1-" :: [Int]
[2,3]
> value .! "[.]0-2" :: [Int]
[1,2]
> value .! "[.]4" :: Maybe Int
Nothing

Construction:

> "." .% True
true

> "{foo}" .% True
{"foo": true}

> "[{foo}]" .% [1,2,3]
[{"foo":1},{"foo":2},{"foo":3}]

> "{foo:[{bar?}]}" .% [Just 1, Nothing]
{"foo":[{"bar":1},{}]}

Performance

Performance is extremely similar to using Aeson functions directly. See Writeup.md for more details.