Remove waargonaut and revert to using aeson.

applied-fp-course.cabal

@@ -86,9 +86,10 @@ library
     , text                  ^>=1.2
     , time                  >=1.4  && <1.10
     , transformers          >=0.4  && <0.6
-    , waargonaut            >=0.6  && <0.9
     , wai                   >=3.2  && <3.4
     , warp                  >=3.2  && <3.4
+    , aeson                 >=1.5  && <3
+    , scientific            >=0.3  && <0.4
 
   -- Directories containing source files.
   hs-source-dirs:   src

flake.nix

@@ -20,12 +20,8 @@
             root = ./.;
 
             overrides = final: prev: with nixpkgs.haskell.lib; {
-              hw-json-simd = dontCheck (unmarkBroken prev.hw-json-simd);
-              hw-json-standard-cursor = doJailbreak prev.hw-json-standard-cursor;
-              natural = dontCheck (unmarkBroken prev.natural);
               sqlite-simple-errors =
                 unmarkBroken (doJailbreak prev.sqlite-simple-errors);
-              waargonaut = dontCheck (doJailbreak prev.waargonaut);
             };
           };
       in

src/Level04/Core.hs

@@ -14,12 +14,12 @@ import           Network.Wai                        (Application, Request,
                                                      strictRequestBody)
 import           Network.Wai.Handler.Warp           (run)
 
+import           Data.Aeson                         (ToJSON, encode)
+import qualified Data.ByteString.Lazy.Char8         as LBS
 import           Network.HTTP.Types                 (Status, hContentType,
                                                      status200, status400,
                                                      status404, status500)
 
-import qualified Data.ByteString.Lazy.Char8         as LBS
-
 import           Data.Either                        (Either (Left, Right),
                                                      either)
 
@@ -30,9 +30,6 @@ import           Data.Text.Lazy.Encoding            (encodeUtf8)
 
 import           Database.SQLite.SimpleErrors.Types (SQLiteResponse)
 
-import           Waargonaut.Encode                  (Encoder')
-import qualified Waargonaut.Encode                  as E
-
 import           Level04.Conf                       (Conf, firstAppConfig)
 import qualified Level04.DB                         as DB
 import           Level04.Types                      (ContentType (JSON, PlainText),
@@ -102,12 +99,11 @@ resp500 =
   mkResponse status500
 
 resp200Json
-  :: Encoder' a
-  -> a
+  :: ToJSON a
+  => a
   -> Response
-resp200Json e =
-  mkResponse status200 JSON . encodeUtf8 .
-  E.simplePureEncodeTextNoSpaces e
+resp200Json =
+  mkResponse status200 JSON . encode
 
 -- |
 app

src/Level04/Types.hs

@@ -16,6 +16,8 @@ module Level04.Types
   , fromDBComment
   ) where
 
+import           Data.Aeson                 (ToJSON (..))
+
 import           GHC.Generics               (Generic)
 
 import           Data.ByteString            (ByteString)
@@ -24,14 +26,9 @@ import           Data.Text                  (Text, pack)
 import           Data.List                  (stripPrefix)
 import           Data.Maybe                 (fromMaybe)
 
-import           Data.Functor.Contravariant ((>$<))
-
 import           Data.Time                  (UTCTime)
 import qualified Data.Time.Format           as TF
 
-import           Waargonaut.Encode          (Encoder)
-import qualified Waargonaut.Encode          as E
-
 import           Level04.DB.Types           (DBComment)
 
 -- | Notice how we've moved these types into their own modules. It's cheap and
@@ -60,15 +57,13 @@ data Comment = Comment
   deriving Show
 
 -- | We're going to write the JSON encoder for our `Comment` type. We'll need to
--- consult the documentation in the 'Waargonaut.Encode' module to find the
+-- consult the documentation in the 'Aeson' package to find the
 -- relevant functions and instructions on how to use them:
 --
--- 'https://hackage.haskell.org/package/waargonaut/docs/Waargonaut-Encode.html'
+-- 'https://hackage.haskell.org/package/aeson/docs/Data-Aeson.html'
 --
-encodeComment :: Applicative f => Encoder f Comment
-encodeComment =
-  error "Comment JSON encoder not implemented"
-  -- Tip: Use the 'encodeISO8601DateTime' to handle the UTCTime for us.
+instance ToJSON Comment where
+  toJSON = error "Comment ToJSON instance no implemented"
 
 -- | For safety we take our stored `DBComment` and try to construct a `Comment`
 -- that we would be okay with showing someone. However unlikely it may be, this
@@ -95,10 +90,4 @@ renderContentType
 renderContentType PlainText = "text/plain"
 renderContentType JSON      = "application/json"
 
-encodeISO8601DateTime :: Applicative f => Encoder f UTCTime
-encodeISO8601DateTime = pack . TF.formatTime loc fmt >$< E.text
-  where
-    fmt = TF.iso8601DateFormat (Just "%H:%M:%S")
-    loc = TF.defaultTimeLocale { TF.knownTimeZones = [] }
-
 -- | Move on to ``src/Level04/DB.hs`` next.

src/Level04/Types/CommentText.hs

@@ -4,13 +4,11 @@ module Level04.Types.CommentText
   , getCommentText
   ) where
 
-import           Waargonaut.Encode          (Encoder)
-import qualified Waargonaut.Encode          as E
+import           Data.Aeson                 (ToJSON (..))
 
 import           Level04.Types.Error        (Error (EmptyCommentText),
                                              nonEmptyText)
 
-import           Data.Functor.Contravariant (contramap)
 import           Data.Text                  (Text)
 
 newtype CommentText = CommentText Text
@@ -52,6 +50,5 @@ getCommentText (CommentText t) =
 -- functions. There is a quick introduction to `Contravariant` in the `README`
 -- for this level.
 --
-encodeCommentText :: Applicative f => Encoder f CommentText
-encodeCommentText = -- Try using 'contramap' and 'E.text'.
-  error "CommentText JSON encoder not implemented"
+instance ToJSON CommentText where
+  toJSON = error "CommentText JSON encoder not implemented"

src/Level04/Types/Topic.hs

@@ -2,11 +2,9 @@ module Level04.Types.Topic
   ( Topic
   , mkTopic
   , getTopic
-  , encodeTopic
   ) where
 
-import           Waargonaut.Encode          (Encoder)
-import qualified Waargonaut.Encode          as E
+import           Data.Aeson                 (ToJSON (..))
 
 import           Data.Functor.Contravariant (contramap)
 import           Data.Text                  (Text)
@@ -28,37 +26,11 @@ getTopic
 getTopic (Topic t) =
   t
 
--- | We will use this function to describe how we would like our `Topic`
--- type to be encoded into JSON.
+-- | We're going to write the JSON encoder for our `Topic` type. We'll need to consult the
+-- documentation in the 'Aeson' package to find the relevant functions and instructions on how to
+-- use them:
 --
--- Waargonaut knows how to encode a `Text` value, we need a way of telling it
--- how to unwrap our newtype to encode the `Text` value inside.
+-- 'https://hackage.haskell.org/package/aeson/docs/Data-Aeson.html'
 --
--- We _could_ write the code to unpack or pattern match on the `Topic` and
--- then run the `Text` encoder using that value as input before returning that
--- as the result of our Encoder. Something like this:
---
--- @
--- encodeA $ \(Topic t) -> runEncoder text t
--- @
---
--- But like many of the tasks that we've been completing in this course, the
--- plumbing for such a thing has already been written for us. Sometimes the
--- instances of the structure we're trying to create may provide a handy
--- shortcut.
---
--- In this case the `Encoder` type has an instance of `Contravariant`. Which has
--- the following function:
---
--- @
--- contramap :: Contravariant f => (a -> b) -> f b -> f a
--- @
---
--- In this case the `Encoder` type has an instance of `Contravariant`. That
--- typeclass has a function that comes in very handy when writing these
--- functions. There is a quick introduction to `Contravariant` in the `README`
--- for this level.
---
-encodeTopic :: Applicative f => Encoder f Topic
-encodeTopic = -- Try using 'contramap' and 'E.text'
-  error "topic JSON encoder not implemented"
+instance ToJSON Topic where
+  toJSON = error "Topic ToJSON instance no implemented"

src/Level05/Core.hs

@@ -28,8 +28,7 @@ import           Data.Text                          (Text)
 import           Data.Text.Encoding                 (decodeUtf8)
 import           Data.Text.Lazy.Encoding            (encodeUtf8)
 
-import           Waargonaut.Encode                  (Encoder')
-import qualified Waargonaut.Encode                  as E
+import           Data.Aeson                         (ToJSON, encode)
 
 import           Database.SQLite.SimpleErrors.Types (SQLiteResponse)
 
@@ -39,7 +38,6 @@ import qualified Level05.DB                         as DB
 import           Level05.Types                      (ContentType (..),
                                                      Error (..),
                                                      RqType (AddRq, ListRq, ViewRq),
-                                                     encodeComment, encodeTopic,
                                                      mkCommentText, mkTopic,
                                                      renderContentType)
 
@@ -116,12 +114,11 @@ resp500 =
   mkResponse status500
 
 resp200Json
-  :: Encoder' a
-  -> a
+  :: ToJSON a
+  => a
   -> Response
-resp200Json e =
-  resp200 JSON . encodeUtf8 .
-  E.simplePureEncodeTextNoSpaces e
+resp200Json =
+  resp200 JSON . encode
 
 -- |
 
@@ -142,8 +139,8 @@ handleRequest db rqType = case rqType of
   -- handles all of that for us. Such is the pleasant nature of these
   -- abstractions.
   AddRq t c -> resp200 PlainText "Success" <$ DB.addCommentToTopic db t c
-  ViewRq t  -> resp200Json (E.list encodeComment) <$> DB.getComments db t
-  ListRq    -> resp200Json (E.list encodeTopic)   <$> DB.getTopics db
+  ViewRq t  -> resp200Json <$> DB.getComments db t
+  ListRq    -> resp200Json <$> DB.getTopics db
 
 mkRequest
   :: Request

src/Level05/Types.hs

@@ -15,8 +15,6 @@ module Level05.Types
   , getCommentText
   , renderContentType
   , fromDBComment
-  , encodeComment
-  , encodeTopic
   ) where
 
 import           GHC.Generics                       (Generic)
@@ -25,12 +23,11 @@ import           GHC.Word                           (Word16)
 import           Data.ByteString                    (ByteString)
 import           Data.Text                          (Text, pack)
 
-import           System.IO.Error                    (IOError)
-
-import           Data.Functor.Contravariant         ((>$<))
+import           Data.Aeson                         (ToJSON (..), object, (.=))
 import           Data.Monoid                        (Last,
                                                      Monoid (mappend, mempty))
 import           Data.Semigroup                     (Semigroup ((<>)))
+import           System.IO.Error                    (IOError)
 
 import           Data.List                          (stripPrefix)
 import           Data.Maybe                         (fromMaybe)
@@ -39,24 +36,19 @@ import qualified Data.Time.Format                   as TF
 
 import           Database.SQLite.SimpleErrors.Types (SQLiteResponse)
 
-import           Waargonaut.Encode                  (Encoder)
-import qualified Waargonaut.Encode                  as E
-
 import           Level05.DB.Types                   (DBComment (dbCommentComment, dbCommentId, dbCommentTime, dbCommentTopic))
 
 import           Level05.Types.CommentText          (CommentText,
-                                                     encodeCommentText,
                                                      getCommentText,
                                                      mkCommentText)
 import           Level05.Types.Error                (Error (DBError, EmptyCommentText, EmptyTopic, UnknownRoute))
-import           Level05.Types.Topic                (Topic, encodeTopic,
-                                                     getTopic, mkTopic)
+import           Level05.Types.Topic                (Topic, getTopic, mkTopic)
 
 newtype CommentId = CommentId Int
   deriving (Show)
 
-encodeCommentId :: Applicative f => Encoder f CommentId
-encodeCommentId = (\(CommentId i) -> i) >$< E.int
+instance ToJSON CommentId where
+  toJSON (CommentId i) = toJSON i
 
 data Comment = Comment
   { commentId    :: CommentId
@@ -66,18 +58,13 @@ data Comment = Comment
   }
   deriving Show
 
-encodeISO8601DateTime :: Applicative f => Encoder f UTCTime
-encodeISO8601DateTime = pack . TF.formatTime tl fmt >$< E.text
-  where
-    fmt = TF.iso8601DateFormat (Just "%H:%M:%S")
-    tl = TF.defaultTimeLocale { TF.knownTimeZones = [] }
-
-encodeComment :: Applicative f => Encoder f Comment
-encodeComment = E.mapLikeObj $ \c ->
-  E.atKey' "id"    encodeCommentId       (commentId c) .
-  E.atKey' "topic" encodeTopic           (commentTopic c) .
-  E.atKey' "text"  encodeCommentText     (commentText c) .
-  E.atKey' "time"  encodeISO8601DateTime (commentTime c)
+instance ToJSON Comment where
+  toJSON c = object
+    [ "id" .= (commentId c)
+    , "topic" .= (commentTopic c)
+    , "text" .= (commentText c)
+    , "time" .= (commentTime c)
+    ]
 
 -- For safety we take our stored DBComment and try to construct a Comment that
 -- we would be okay with showing someone. However unlikely it may be, this is a

src/Level05/Types/CommentText.hs

@@ -2,23 +2,19 @@ module Level05.Types.CommentText
   ( CommentText
   , mkCommentText
   , getCommentText
-  , encodeCommentText
   ) where
 
-import           Waargonaut.Encode          (Encoder)
-import qualified Waargonaut.Encode          as E
+import           Level05.Types.Error (Error (EmptyCommentText), nonEmptyText)
 
-import           Level05.Types.Error        (Error (EmptyCommentText),
-                                             nonEmptyText)
+import           Data.Aeson          (ToJSON (..))
 
-import           Data.Functor.Contravariant ((>$<))
-import           Data.Text                  (Text)
+import           Data.Text           (Text)
 
 newtype CommentText = CommentText Text
   deriving (Show)
 
-encodeCommentText :: Applicative f => Encoder f CommentText
-encodeCommentText = getCommentText >$< E.text
+instance ToJSON CommentText where
+  toJSON (CommentText t) = toJSON t
 
 mkCommentText
   :: Text

src/Level05/Types/Topic.hs

@@ -2,22 +2,19 @@ module Level05.Types.Topic
   (Topic
   , mkTopic
   , getTopic
-  , encodeTopic
   ) where
 
-import           Waargonaut.Encode          (Encoder)
-import qualified Waargonaut.Encode          as E
+import           Level05.Types.Error (Error (EmptyTopic), nonEmptyText)
 
-import           Level05.Types.Error        (Error (EmptyTopic), nonEmptyText)
+import           Data.Aeson          (ToJSON (..))
 
-import           Data.Functor.Contravariant ((>$<))
-import           Data.Text                  (Text)
+import           Data.Text           (Text)
 
 newtype Topic = Topic Text
   deriving Show
 
-encodeTopic :: Applicative f => Encoder f Topic
-encodeTopic = getTopic >$< E.text
+instance ToJSON Topic where
+  toJSON (Topic t) = toJSON t
 
 mkTopic
   :: Text