Roundtrip Aeson

roundtrip allows you to write invertible syntax descriptions -- or, to put it another way, a parser and pretty printer combined -- for String or XML data. This package extends this to support constructing and destructing JSON documents.

Example

Using roundtrip-aeson is relatively straightforward:

1. Define your data type;

2. Define partial isomorphisms for the constructors (probably using the template haskell);

3. Describe the syntax of its JSON representation; and

4. Use that representation to build and parse JSON.

import Data.Aeson.RoundTrip

data Invoice
    = Unpaid Bool Integer Bool
    | Paid Double
  deriving (Show)

defineIsomorphisms ''Invoice

invoiceSyntax :: JsonSyntax s => s Invoice
invoiceSyntax =
    unpaid
        <$> jsonField "overdue" jsonBool
        <*> jsonField "total"   jsonIntegral
        <*> jsonField "warned"  jsonBool
    <|> paid
        <$> jsonField "total"   jsonRealFrac

main :: IO ()
main = do
    -- Build a JSON representation.
    let Right x = runBuilder invoiceSyntax $ Unpaid False 40 [False]
    L.putStrLn $ encode x
    -- Parse a JSON representation.
    print $ runParser invoiceSyntax x

See tests/demo.hs for the complete source of this example.