Merge pull request #88 from qfpl/semigroup-last

Last from Monoid is deprecated, use the one from Semigroup

src/Level06/Conf/CommandLine.hs

@@ -2,7 +2,7 @@ module Level06.Conf.CommandLine
   ( commandLineParser
   ) where
 
-import           Data.Monoid         (Last (Last), (<>))
+import           Data.Semigroup      (Last (Last), (<>))
 
 import           Options.Applicative (Parser, eitherReader, execParser,
                                       fullDesc, header, help, helper, info,
@@ -11,7 +11,7 @@ import           Options.Applicative (Parser, eitherReader, execParser,
 
 import           Text.Read           (readEither)
 
-import           Level06.Types      (DBFilePath (DBFilePath),
+import           Level06.Types       (DBFilePath (DBFilePath),
                                       PartialConf (PartialConf), Port (Port))
 
 -- | Command Line Parsing
@@ -36,7 +36,7 @@ partialConfParser =
 
 -- Parse the Port value off the command line args and into a Last wrapper.
 portParser
-  :: Parser (Last Port)
+  :: Parser (Maybe (Last Port))
 portParser =
   let
     mods = long "port"
@@ -46,11 +46,11 @@ portParser =
     -- A custom parser to turn a String into a Word16, before putting it into a Port
     portReader = eitherReader (fmap Port . readEither)
   in
-    Last <$> optional (option portReader mods)
+    fmap Last <$> optional (option portReader mods)
 
 -- Parse the DBFilePath from the input string into our type and into a Last wrapper.
 dbFilePathParser
-  :: Parser (Last DBFilePath)
+  :: Parser (Maybe (Last DBFilePath))
 dbFilePathParser =
   let
     mods = long "db-filepath"
@@ -58,4 +58,4 @@ dbFilePathParser =
            <> metavar "DBFILEPATH"
            <> help "File path for our SQLite Database file."
   in
-    Last <$> optional (DBFilePath <$> strOption mods)
+    fmap Last <$> optional (DBFilePath <$> strOption mods)

src/Level06/Types.hs

@@ -36,9 +36,7 @@ import           Data.Text                          (Text, pack)
 
 import           System.IO.Error                    (IOError)
 
-import           Data.Monoid                        (Last (..),
+import           Data.Semigroup                     (Last (..), Semigroup ((<>)))
-                                                     Monoid (mappend, mempty))
-import           Data.Semigroup                     (Semigroup ((<>)))
 
 import           Data.Functor.Contravariant         ((>$<))
 import           Data.List                          (stripPrefix)
@@ -172,8 +170,8 @@ confPortToWai
 confPortToWai =
   error "confPortToWai not implemented"
 
--- Similar to when we were considering our application types. We can add to this sum type as we
+-- Similar to when we were considering our application types. We can add to this sum type
--- build our application and the compiler can help us out.
+-- as we build our application and the compiler can help us out.
 data ConfigError
   = BadConfFile DecodeError
   deriving Show
@@ -189,40 +187,31 @@ data ConfigError
 
 -- ``defaults <> file <> commandLine``
 
--- We can use the ``Monoid`` typeclass to handle combining the ``Conf`` records
+-- We can use the ``Semigroup`` typeclass to handle combining the ``Conf`` records
 -- together, and the ``Last`` type to wrap up our values to handle the desired
 -- precedence. The ``Last`` type is a wrapper for Maybe that when used with its
--- ``Monoid`` instance will always preference the last ``Just`` value that it
+-- ``Semigroup`` instance will always preference the last value that it has:
--- has:
+--
-
+-- Just (Last 3) <> Just (Last 1) = Just (Last 1)
--- Last (Just 3) <> Last (Just 1) = Last (Just 1)
+-- Nothing       <> Just (Last 1) = Just (Last 1)
--- Last Nothing  <> Last (Just 1) = Last (Just 1)
+-- Just (Last 1) <> Nothing       = Just (Last 1)
--- Last (Just 1) <> Last Nothing  = Last (Just 1)
+--
-
+-- To make this easier, we'll make a new type ``PartialConf`` that will have our ``Last``
--- To make this easier, we'll make a new type ``PartialConf`` that will have our
+-- wrapped values. We can then define a ``Semigroup`` instance for it and have our
--- ``Last`` wrapped values. We can then define a ``Monoid`` instance for it and
+-- ``Conf`` be a known good configuration.
--- have our ``Conf`` be a known good configuration.
 data PartialConf = PartialConf
-  { pcPort       :: Last Port
+  { pcPort       :: Maybe (Last Port)
-  , pcDBFilePath :: Last DBFilePath
+  , pcDBFilePath :: Maybe (Last DBFilePath)
   }
 
--- Before we can define our ``Monoid`` instance for ``PartialConf``, we'll have
+-- We need to define a ``Semigroup`` instance for ``PartialConf``. We define our ``(<>)``
--- to define a Semigroup instance. We define our ``(<>)`` function to lean
+-- function to lean on the ``Semigroup`` instance for Last to always get the last value.
--- on the ``Semigroup`` instance for Last to always get the last value.
 instance Semigroup PartialConf where
   _a <> _b = PartialConf
     { pcPort       = error "pcPort (<>) not implemented"
     , pcDBFilePath = error "pcDBFilePath (<>) not implemented"
     }
 
--- We now define our ``Monoid`` instance for ``PartialConf``. Allowing us to
--- define our always empty configuration, which would always fail our
--- requirements. We just define `mappend` to be an alias of ``(<>)``
-instance Monoid PartialConf where
-  mempty = PartialConf mempty mempty
-  mappend = (<>)
-
 -- | When it comes to reading the configuration options from the command-line, we
 -- use the 'optparse-applicative' package. This part of the exercise has already
 -- been completed for you, feel free to have a look through the 'CommandLine'

src/Level07/Conf.hs

@@ -7,7 +7,7 @@ module Level07.Conf
 import           GHC.Word                  (Word16)
 
 import           Data.Bifunctor            (first)
-import           Data.Monoid               (Last (..), (<>))
+import           Data.Semigroup            (Last (..), (<>))
 
 import           Level07.Types            (Conf (..), ConfigError (..),
                                             DBFilePath (DBFilePath),
@@ -21,8 +21,8 @@ import           Level07.Conf.File        (parseJSONConfigFile)
 defaultConf
   :: PartialConf
 defaultConf = PartialConf
-  (pure (Port 3000))
+  (pure (Last $ Port 3000))
-  (pure (DBFilePath "app_db.db"))
+  (pure (Last $ DBFilePath "app_db.db"))
 
 -- We need something that will take our PartialConf and see if can finally build
 -- a complete Conf record. Also we need to highlight any missing config values
@@ -39,10 +39,10 @@ makeConfig pc = Conf
     -- like to be explicit in your intentions.
     lastToEither
       :: ConfigError
-      -> (PartialConf -> Last b)
+      -> (PartialConf -> Maybe (Last b))
       -> Either ConfigError b
     lastToEither e g =
-      (maybe (Left e) Right . getLast . g) pc
+      maybe (Left e) (Right . getLast) . g $ pc 
 
 -- This is the function we'll actually export for building our configuration.
 -- Since it wraps all our efforts to read information from the command line, and

src/Level07/Conf/CommandLine.hs

@@ -2,7 +2,7 @@ module Level07.Conf.CommandLine
   ( commandLineParser
   ) where
 
-import           Data.Monoid         (Last (Last), (<>))
+import           Data.Semigroup      (Last (Last), (<>))
 
 import           Options.Applicative (Parser, eitherReader, execParser,
                                       fullDesc, header, help, helper, info,
@@ -11,7 +11,7 @@ import           Options.Applicative (Parser, eitherReader, execParser,
 
 import           Text.Read           (readEither)
 
-import           Level07.Types      (DBFilePath (DBFilePath),
+import           Level07.Types       (DBFilePath (DBFilePath),
                                       PartialConf (PartialConf), Port (Port))
 
 -- | Command Line Parsing
@@ -36,7 +36,7 @@ partialConfParser =
 
 -- Parse the Port value off the command line args and into a Last wrapper.
 portParser
-  :: Parser (Last Port)
+  :: Parser (Maybe (Last Port))
 portParser =
   let
     mods = long "port"
@@ -46,11 +46,11 @@ portParser =
     -- A custom parser to turn a String into a Word16, before putting it into a Port
     portReader = eitherReader (fmap Port . readEither)
   in
-    Last <$> optional (option portReader mods)
+    fmap Last <$> optional (option portReader mods)
 
 -- Parse the DBFilePath from the input string into our type and into a Last wrapper.
 dbFilePathParser
-  :: Parser (Last DBFilePath)
+  :: Parser (Maybe (Last DBFilePath))
 dbFilePathParser =
   let
     mods = long "db-filepath"
@@ -58,4 +58,4 @@ dbFilePathParser =
            <> metavar "DBFILEPATH"
            <> help "File path for our SQLite Database file."
   in
-    Last <$> optional (DBFilePath <$> strOption mods)
+    fmap Last <$> optional (DBFilePath <$> strOption mods)

src/Level07/Types.hs

@@ -32,8 +32,7 @@ import           Data.ByteString                    (ByteString)
 import           Data.Text                          (pack)
 
 import           Data.Functor.Contravariant         ((>$<))
-import           Data.Monoid                        (Last (Last))
+import           Data.Semigroup                     (Last (Last), Semigroup ((<>)))
-import           Data.Semigroup                     (Semigroup ((<>)))
 
 import           Data.Time                          (UTCTime)
 import qualified Data.Time.Format                   as TF
@@ -162,51 +161,42 @@ data ConfigError
   | ConfigFileReadError IOError
   deriving Show
 
--- Our application will be able to load configuration from both a file and
+-- Our application will be able to load configuration from both a file and command line
--- command line input. We want to be able to use the command line to temporarily
+-- input. We want to be able to use the command line to temporarily override the
--- override the configuration from our file. How do we combine the different
+-- configuration from our file. How do we combine the different inputs to enable this
--- inputs to enable this property?
+-- property?
 
--- We want the command line configuration to take precedence over the File
+-- We want the command line configuration to take precedence over the File configuration,
--- configuration, so if we think about combining each of our ``Conf`` records,
+-- so if we think about combining each of our ``Conf`` records, we want to be able to
--- we want to be able to write something like this:
+-- write something like this:
 
 -- ``defaults <> file <> commandLine``
 
--- We can use the ``Monoid`` typeclass to handle combining the ``Conf`` records
+-- We can use the ``Semigroup`` typeclass to handle combining the ``Conf`` records
 -- together, and the ``Last`` type to wrap up our values to handle the desired
 -- precedence. The ``Last`` type is a wrapper for Maybe that when used with its
--- ``Monoid`` instance will always preference the last ``Just`` value that it
+-- ``Semigroup`` instance will always preference the last value that it has:
--- has:
+--
-
+-- Just (Last 3) <> Just (Last 1) = Just (Last 1)
--- Last (Just 3) <> Last (Just 1) = Last (Just 1)
+-- Nothing       <> Just (Last 1) = Just (Last 1)
--- Last Nothing  <> Last (Just 1) = Last (Just 1)
+-- Just (Last 1) <> Nothing       = Just (Last 1)
--- Last (Just 1) <> Last Nothing  = Last (Just 1)
+--
-
+-- To make this easier, we'll make a new type ``PartialConf`` that will have our ``Last``
--- To make this easier, we'll make a new type ``PartialConf`` that will have our
+-- wrapped values. We can then define a ``Semigroup`` instance for it and have our
--- ``Last`` wrapped values. We can then define a ``Monoid`` instance for it and
+-- ``Conf`` be a known good configuration.
--- have our ``Conf`` be a known good configuration.
 data PartialConf = PartialConf
-  { pcPort       :: Last Port
+  { pcPort       :: Maybe (Last Port)
-  , pcDBFilePath :: Last DBFilePath
+  , pcDBFilePath :: Maybe (Last DBFilePath)
   }
 
--- Before we can define our ``Monoid`` instance for ``PartialConf``, we'll have
+-- We need to define a ``Semigroup`` instance for ``PartialConf``. We define our ``(<>)``
--- to define a Semigroup instance. We define our ``(<>)`` function to lean
+-- function to lean on the ``Semigroup`` instance for Last to always get the last value.
--- on the ``Semigroup`` instance for Last to always get the last value.
 instance Semigroup PartialConf where
   a <> b = PartialConf
     { pcPort       = pcPort a <> pcPort b
     , pcDBFilePath = pcDBFilePath a <> pcDBFilePath b
     }
 
--- We now define our ``Monoid`` instance for ``PartialConf``. Allowing us to
--- define our always empty configuration, which would always fail our
--- requirements. We just define `mappend` to be an alias of ``(<>)``
-instance Monoid PartialConf where
-  mempty = PartialConf mempty mempty
-  mappend = (<>)
-
 -- When it comes to reading the configuration options from the command-line, we
 -- use the 'optparse-applicative' package. This part of the exercise has already
 -- been completed for you, feel free to have a look through the 'CommandLine'
@@ -221,7 +211,7 @@ partialConfDecoder = PartialConf
   <$> lastAt "port" D.integral Port
   <*> lastAt "dbFilePath" D.string DBFilePath
   where
-    lastAt k d c = Last . fmap c <$> D.atKeyOptional k d
+    lastAt k d c = fmap (Last . c) <$> D.atKeyOptional k d
 
 -- We have a data type to simplify passing around the information we need to run
 -- our database queries. This also allows things to change over time without