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": [*, *]}] Â Â |
[{a,b}] |
[(a, [c])] |
| Array of objects | [{"foo": *}] |
[{foo}] |
[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
NothingConstruction:
> "." .% 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. Benchmarks are also included.
