Simplify command system

All that type class and language extension madness was completely and utterly
unnecessary, but I only noticed it after I had already pushed the
implementation. Oh well ¯\_(ツ)_/¯

src/Haboli/Euphoria/Command.hs

@@ -1,14 +1,7 @@
-{-# LANGUAGE ExistentialQuantification #-}
-{-# LANGUAGE MultiParamTypeClasses     #-}
-
--- | This module provides an abstraction for bot commands in the form of the
--- 'Hook' type class and the 'Command' type.
+-- | This module provides an abstraction for bot commands.
 
 module Haboli.Euphoria.Command
-  ( Hook(..)
-  , Command
-  , cmd
-  , runCommand
+  ( Command
   , runCommands
   , respondingToCommands
   ) where
@@ -18,34 +11,16 @@ import           Control.Monad
 import           Haboli.Euphoria.Api
 import           Haboli.Euphoria.Client
 
--- | A hook is a way to react to new messages in a room. These typically don't
--- include the messages sent by the client itself.
-class Hook h where
-  -- | @reel h msg@ applies the hook @h@ to the 'Message' @msg@. If no further
-  -- hooks should be applied to this message, it should return 'True'.
-  -- Otherwise, it should return 'False'.
-  reel :: h e -> Message -> Client e Bool
-
--- | A wrapper around hooks that allows for heterogenous lists of hooks. In
--- other words, it lets you combine different 'Hook' instances into a single
--- list.
-data Command e = forall h. (Hook h) => Command (h e)
-
--- | Wrap a hook. Notice how the @h@ type disappears: This function can convert
--- different 'Hook' instances into the same type.
-cmd :: (Hook h) => h e -> Command e
-cmd = Command
-
--- | Apply a 'Command' to a 'Message'. For more information, see 'reel'.
-runCommand :: Command e -> Message -> Client e Bool
-runCommand (Command h) = reel h
+-- | If a command should block any further commands from executing on a message,
+-- it should return 'True'. Otherwise. it should return 'False'.
+type Command e = Message -> Client e Bool
 
 -- | Apply multiple 'Command's to a 'Message' in order until one returns 'True'.
 -- All commands following that one are not applied.
 runCommands :: [Command e] -> Message -> Client e Bool
 runCommands [] _ = pure False
 runCommands (c:cs) msg = do
-  abort <- runCommand c msg
+  abort <- c msg
   if abort
     then pure True
     else runCommands cs msg