Got rid of ! in Server.hs via better lensing

src/Pipes/IRC/Server/Server.hs

@@ -20,11 +20,9 @@ module Pipes.IRC.Server.Server
 where
 
 import           Control.Lens
-import           Data.Map                 ((!))
 import qualified Data.Map                 as M
 import           Data.Maybe
 import qualified Data.Set                 as S
-
 import           Pipes.IRC.Server.Channel
 import           Pipes.IRC.Server.Types
 import           Pipes.IRC.Server.User
@@ -46,14 +44,14 @@ ircDelUser :: NickKey   -- ^ nickname of the user to delete
            -> IrcServer -- ^ server to delete the user from
            -> IrcServer -- ^ new server with user deleted
 ircDelUser nn srv =
-  srv & ircNicks %~ S.delete nn
-      & if M.notMember nn (srv ^. ircUsers) then id else
+  srv & ircNicks %~ sans nn
+      & if isn't _Just (srv ^. ircUsers . at nn) then id else
         let
-           usr = (srv ^. ircUsers) ! nn
-           uchans = S.elems (usr ^. userChannels)
-           ichans = S.elems (usr ^. userInvites)
+           usr = srv ^. ircUsers . at nn
+           uchans = usr ^. traverse . userChannels . to S.elems
+           ichans = usr ^. traverse . userInvites . to S.elems
         in
-           (ircUsers    %~ M.delete nn)
+           (ircUsers    %~ sans nn)
          . (ircChannels %~ alterAtKeys (ircPartChan nn) uchans)
          . (ircChannels %~ adjustAtKeys (chanDelInvite nn) ichans)
 
@@ -105,8 +103,8 @@ ircPart uname cn srv =
   srv & (ircChannels %~ (M.alter $ ircPartChan uname) cn)
       & (ircUsers    %~ adjustAtKeys (userDelInvite cn) iusers)
   where
-    chan = (srv ^. ircChannels) ! cn
-    iusers = S.elems $ chan ^. chanInvites
+    chan = srv ^. ircChannels . at cn
+    iusers = chan ^. traverse . chanInvites . to S.elems
 
 -- | Add the user with the given nickname to the invited list for the
 -- channel, and add the channel to the user's invited list.
@@ -146,9 +144,9 @@ ircChangeNick old new srv =
   if M.notMember old (srv ^. ircUsers) then
      srv
   else let
-     usr = (srv ^. ircUsers) ! old
-     chs = S.elems (usr ^. userChannels)
+     usr = srv ^. ircUsers . at old
+     chs = usr ^. traverse . userChannels . to S.elems
   in
-     srv & (ircNicks    %~ S.delete old . S.insert new)
-         & (ircUsers    %~ M.delete old . M.insert new usr)
+     srv & (ircNicks    %~ sans old . S.insert new)
+         & (ircUsers    %~ sans old . (at new .~ usr))
          & (ircChannels %~ adjustAtKeys (chanChangeNick old new) chs)