foo.hs

{-# LANGUAGE DeriveGeneric #-}  -- for JTask and Fields ToJSON instances:w!
{-# LANGUAGE FlexibleInstances #-} -- for the HashMap ToJSON instances
{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE OverloadedStrings #-}

import Prelude
import Data.ByteString
import GHC.Generics (Generic )
import Data.Aeson
import Data.HashMap.Strict (HashMap)
import qualified Data.HashMap.Strict as HashMap
import Data.Hashable
import Data.ByteString.Char8 ()

data JTask = JTask {fields :: Fields} deriving (Generic)
data Fields = Fields { project :: HashMap Key Project
                     , summary :: ByteString
                     , issuetype :: HashMap Name Task
                     , versions :: [HashMap Name Version]
                     , description :: ByteString
                     } deriving (Generic)

data Key = Key deriving (Generic)

instance Hashable Key where
   hash _ = 0

instance Show Key where
   show Key = "key"

data Name = Name deriving (Generic)

instance Hashable Name where
   hash _ = 0

instance Show Name where
   show Name = "name"

data Task = Task deriving (Generic)

instance Hashable Task where
   hash _ = 0

type Version = ByteString -- Placeholder type. Probably using Day for realsies.

data Project = BNAP deriving (Generic) -- Fill this out as we go 

instance ToJSON Fields
instance ToJSON JTask 

instance ToJSON Key
instance ToJSON Name
instance ToJSON Task
instance ToJSON Project

mapfst :: (a -> b) -> [(a, v)] -> [(b, v)]
mapfst f = fmap $ \ (k, v) -> (f k, v)

instance ToJSON a => ToJSON (HashMap Key a) where
  toJSON = toJSON . HashMap.fromList . mapfst show . HashMap.toList

instance ToJSON a => ToJSON (HashMap Name a) where
  toJSON = toJSON . HashMap.fromList . mapfst show . HashMap.toList

createObject :: Value
createObject =
    toJSON
  . JTask
  $ Fields { project = HashMap.singleton Key BNAP
           , summary = "summary"
           , issuetype = HashMap.singleton Name Task
           , versions = [HashMap.singleton Name ("version")]
           , description = "description"
           }

gistfile1.txt

*Main Data.ByteString.Lazy> Data.ByteString.Lazy.putStrLn (encode createObject)
{"fields":{"project":{"key":[]},"description":"description","issuetype":{"name":[]},"summary":"summary","versions":[{"name":"version"}]}}