Add ToJSON instances for IntN, UintN and generated datatypes

[RubenAstudillo]

Motivation

From the Network.Ethereum.Contract.TH module we can generate native ADTs to events specified on a contract ABIs. This is great if the rest of you project uses exclusively Haskell, but if you need to play along another languages or ecosystems, having a common representation such a JSON is necessary. This PR adds ToJSON instances for all events types (not internal Data$ nor Indexed$ ADTs though).

Changes

• Add missing ToJSON instances for UintN and IntN.
• Add aeson-casing dependency
• Add ToJSON instances for generated datatypes using Generic deriving (aeson default).

Known infelicities

The init' function I use to recover the input name from the record selector of an ADT is a hack. The correct way should be to obtain that name from the eveArgName field on the inputs. But if I follow path, I would have to write custom code for instance generation, losing the benefits of using the Generic instance. It is a tradeoff and I choose succinctness.

Tests

I have been using this for 1 month, storing the JSONs produced on a postgresql database. So far the output matches what I would expect.

For a event declared like this

  {
    "anonymous": false,
    "inputs": [
      {
        "indexed": true,
        "internalType": "address",
        "name": "from",
        "type": "address"
      },
      {
        "indexed": true,
        "internalType": "address",
        "name": "to",
        "type": "address"
      },
      {
        "indexed": true,
        "internalType": "uint256",
        "name": "tokenId",
        "type": "uint256"
      }
    ],
    "name": "Transfer",
    "type": "event"
  },

We generate the following instance

ghci> toJSON (Transfer def def 1000)
Object (fromList [("from",String "0x0000000000000000000000000000000000000000"),("to",String "0x0000000000000000000000000000000000000000"),("tokenId",Number 1000.0)])

On anohter event with arguments prefixed by _

  {
    "anonymous": false,
    "inputs": [
      {
        "indexed": true,
        "name": "_bidder",
        "type": "address"
      },
      {
        "indexed": true,
        "name": "_editionNumber",
        "type": "uint256"
      },
      {
        "indexed": true,
        "name": "_tokenId",
        "type": "uint256"
      },
      {
        "indexed": false,
        "name": "_amount",
        "type": "uint256"
      }
    ],
    "name": "BidAccepted",
    "type": "event"
  },

The json instance is

ghci> toJSON (BidAccepted def 100 100 150)
Object (fromList [("_amount",Number 150.0),("_bidder",String "0x0000000000000000000000000000000000000000"),("_editionNumber",Number 100.0),("_tokenId",Number 100.0)])

License

Copyright belongs to SuperRare Labs. It is licensed under the Apache 2.0 terms as the rest of this project. If another license is needed with more liberal terms we can accommodate that. Thank you for all your work on this library!

[akru]

Amazing, thank you!