Replace Prelude with RIO

I believe RIO stands for: "ReaderT <something-something> IO", which is a nod to
the top-level application data type:

```haskell
-- This is a simplification
newtype RIO env a = RIO { runRIO :: ReaderT env a () }
```

I read about RIO from an FP-Complete blog post a few months ago, and now I'm
excited to try it out for a real project. Bon voyage!

1 files changed, 20 insertions, 2 deletions

diff --git a/website/sandbox/learnpianochords/src/server/Types.hs b/website/sandbox/learnpianochords/src/server/Types.hs
index 5b8ca036dd0b..3a9decf39c19 100644
--- a/website/sandbox/learnpianochords/src/server/Types.hs
+++ b/website/sandbox/learnpianochords/src/server/Types.hs
@@ -1,12 +1,30 @@
 --------------------------------------------------------------------------------
 module Types where
 --------------------------------------------------------------------------------
+import RIO
 import Data.Aeson
-import Data.Text
+import System.Envy (FromEnv, fromEnv, env)
 --------------------------------------------------------------------------------
 
+-- | Read from .envrc
+data Env = Env
+  { envGoogleClientID :: !String
+  } deriving (Eq, Show)
+
+instance FromEnv Env where
+  fromEnv _ = do
+    envGoogleClientID <- env "GOOGLE_CLIENT_ID"
+    pure Env {..}
+
+-- | Application context: a combination of Env and additional values.
+data Context = Context
+  { contextGoogleClientID :: !String
+  , contextServerPort :: !Int
+  , contextClientPort :: !Int
+  }
+
 data VerifyGoogleSignInRequest = VerifyGoogleSignInRequest
-  { idToken :: Text
+  { idToken :: !Text
   } deriving (Eq, Show)
 
 instance FromJSON VerifyGoogleSignInRequest where