Description
Quick JSON extractions with Aeson.
Description
Small DSL on top of Aeson for casual and concise JSON construction and deconstruction.
README.md
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.