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free-monad-example
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Lib: Changes to the DSL 

1. Fix the logger DSL and add top level helpers
2. Drop the servant server part in the DSL. As aptly explained by Arun,
"It won't accomplish a lot to DSL-ise the starting of that execution
flow -- it's not expressing any business logic, just setting up the
scaffolding within which our business logic will be executed".

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
This commit is contained in:
Sanchayan Maity 2020-07-27 20:32:43 +05:30
parent 7547bcefad
commit 38d9cd6072
1 changed files with 10 additions and 29 deletions
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39
src/Lib.hs
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@ -9,10 +9,7 @@ module Lib where
import Control.Exception
import Control.Monad.Free.Church
import Database.PostgreSQL.Simple
import Data.Proxy
import Data.Text
import Servant.API
import Servant.Server
data SqlDBMethodF next where
SqlDBMethod :: FromRow r => (Connection -> Query -> IO [r]) -> ([r] -> next) -> SqlDBMethodF next
@ -37,25 +34,6 @@ interpretSqlDBMethod _ _ (SqlThrowException exception _) = throwIO exception
runDB :: Connection -> Query -> SqlDb a -> IO a
runDB conn squery = foldF $ interpretSqlDBMethod conn squery
type SampleAPI = Get '[JSON] Text
data ServeF next where
ServeMethod :: (forall api. HasServer api '[] => (Proxy api -> IO a)) -> (a -> next) -> ServeF next
instance Functor ServeF where
fmap f (ServeMethod runner next) = ServeMethod runner (f . next)
type Serve = F ServeF
serveMethod :: (forall api. HasServer api '[] => (Proxy api -> IO a)) -> Serve a
serveMethod action = liftF $ ServeMethod action id
interpretServeMethod :: HasServer api '[] => Proxy api -> ServeF a -> IO a
interpretServeMethod api (ServeMethod runner next) = next <$> runner api
runServe :: HasServer api '[] => Proxy api -> Serve a -> IO a
runServe api = foldF $ interpretServeMethod api
data LoggerMethodF next where
LogMessage :: Text -> (() -> next) -> LoggerMethodF next
@ -65,22 +43,20 @@ instance Functor LoggerMethodF where
type Logger = F LoggerMethodF
logMessage :: Text -> Logger ()
logMessage logMsg = liftF $ LogMessage logMsg id
logMessage msg = liftF $ LogMessage msg id
interpretLoggerMethod :: LoggerMethodF a -> IO a
interpretLoggerMethod (LogMessage msg next) = next <$> print msg
runLogger :: Logger a -> IO a
runLogger :: Logger () -> IO ()
runLogger = foldF interpretLoggerMethod
data DSLMethod next where
LogMsg :: Logger () -> (() -> next) -> DSLMethod next
ServeHttp :: HasServer api '[] => Proxy api -> Serve a -> (a -> next) -> DSLMethod next
RunQuery :: FromRow r => Connection -> Query -> SqlDb [r] -> ([r] -> next) -> DSLMethod next
instance Functor DSLMethod where
fmap f (LogMsg msg next) = LogMsg msg (f . next)
fmap f (ServeHttp api act next) = ServeHttp api act (f . next)
fmap f (RunQuery conn squery act next) = RunQuery conn squery act (f . next)
type DSL = F DSLMethod
@ -88,10 +64,15 @@ type DSL = F DSLMethod
interpretDSLMethod :: DSLMethod a -> IO a
interpretDSLMethod (LogMsg logger next) =
fmap next $ runLogger logger
interpretDSLMethod (ServeHttp api server next) =
fmap next $ runServe api server
interpretDSLMethod (RunQuery conn squery sql next) =
fmap next $ runDB conn squery sql
runDSL :: DSL a -> IO a
runDSL :: DSL () -> IO ()
runDSL = foldF interpretDSLMethod
-- Smart constructors providing a convenient interface.
logMsg :: Text -> DSL ()
logMsg msg = liftF $ LogMsg (logMessage msg) id
runQuery :: (MonadFree DSLMethod m, FromRow r) => Connection -> Query -> m [r]
runQuery conn squery = liftF $ RunQuery conn squery (sqlDbMethod query_) id