Eved - A Value Level Servant Replacement

Eved is an API definition eDSL in the spirit of Servant. The main difference from Servant is that Eved is a value level API, whereas Servant relies very heavily on fancy type level programming.

Eved is highly extensible (both in terms of implementations and new terms) thanks to its utilization of the so called final tagless encoding.

Example

Api Definition

import           Data.Text              (Text)
import           Web.Eved
import qualified Web.Eved.ContentType   as CT
import qualified Web.Eved.QueryParam    as QP
import qualified Web.Eved.UrlElement    as UE

type Api m =
       (Integer -> Integer -> m Integer)
  :<|> (Text    -> Integer -> m Integer)
  :<|> (Text    -> Integer -> m Integer)

api :: Eved api m => api (Api m)
api =
      (lit "v1" .</> capture "captureNum" UE.integer .</> queryParam "arg1" QP.integer .</> get [CT.json @Integer])
 .<|> (lit "v1" .</> capture "captureText" UE.text .</> reqBody [CT.json @Integer] .</> post [CT.json @Integer])
 .<|> (lit "v2" .</> capture "captureText" UE.text .</> queryParam "arg1" QP.integer .</> get [CT.json @Integer])

Client

import           Web.Eved.Client

v1CaptureNum :<|> v1CaptureText :<|> v2CaptureText = getClient api "http://localhost:3000"

Server

import           Control.Monad.IO.Class
import           Control.Monad.Reader
import           Web.Eved.Server
import           Network.Wai.Handler.Warp

serve :: IO ()
serve = run 3000 $ server (`runReaderT` (Env 100)) handlers api

data Env = Env
    { envSecret :: Integer
    }

handlers :: (MonadIO m, MonadReader Env m) => Api m
handlers =   (\a b -> pure $ a + b)
        :<|> (\_ i -> fmap ((+) i) (asks envSecret))
        :<|> (\_ i -> pure i)

Prior Art

TODO

How to extend the language

TODO