diff --git a/butcher.cabal b/butcher.cabal
index bed47f4..b56cbfc 100644
--- a/butcher.cabal
+++ b/butcher.cabal
@@ -42,12 +42,12 @@ library
   other-modules:       UI.Butcher.Monadic.Internal.Types
                        UI.Butcher.Monadic.Internal.Core
   build-depends:
-    { base >=4.8 && <4.11
+    { base >=4.9 && <4.12
     , free
     , unsafe
     , microlens <0.5
     , microlens-th <0.5
-    , multistate
+    , multistate >=0.8 && <0.9
     , pretty
     , containers
     , transformers
@@ -103,7 +103,7 @@ test-suite tests
   type:             exitcode-stdio-1.0
   default-language: Haskell2010
   build-depends:
-    { base >=4.8 && <4.11
+    { base <999
     , butcher
     , free
     , unsafe
diff --git a/iridium.yaml b/iridium.yaml
index 682b300..7636457 100644
--- a/iridium.yaml
+++ b/iridium.yaml
@@ -21,12 +21,12 @@ checks:
     location: "ChangeLog.md"
   compiler-versions:
     compilers:
-      - compiler: "ghc"
-        version: "7.10.3"
       - compiler: "ghc"
         version: "8.0.2"
       - compiler: "ghc"
-        version: "8.2.1"
+        version: "8.2.2"
+      - compiler: "ghc"
+        version: "8.4.1"
     compilers-help: |
       for this to work, cabal will need the paths to the actual
       compilers to be configured; see the note about the user-global
diff --git a/src/UI/Butcher/Monadic/Flag.hs b/src/UI/Butcher/Monadic/Flag.hs
index 0fd8119..25fa69d 100644
--- a/src/UI/Butcher/Monadic/Flag.hs
+++ b/src/UI/Butcher/Monadic/Flag.hs
@@ -80,14 +80,20 @@ data Flag p = Flag
   , _flag_visibility :: Visibility
   }
 
+appendFlag :: Flag p -> Flag p -> Flag p
+appendFlag (Flag a1 b1 c1) (Flag a2 b2 c2) = Flag (a1 <|> a2)
+                                                  (b1 <|> b2)
+                                                  (appVis c1 c2)
+ where
+  appVis Visible Visible = Visible
+  appVis _       _       = Hidden
+
+instance Semigroup (Flag p) where
+  (<>) = appendFlag
+
 instance Monoid (Flag p) where
   mempty = Flag Nothing Nothing Visible
-  Flag a1 b1 c1 `mappend` Flag a2 b2 c2 = Flag (a1 <|> a2)
-                                               (b1 <|> b2)
-                                               (appVis c1 c2)
-   where
-    appVis Visible Visible = Visible
-    appVis _       _       = Hidden
+  mappend = appendFlag
 
 -- | Create a 'Flag' with just a help text.
 flagHelp :: PP.Doc -> Flag p
diff --git a/src/UI/Butcher/Monadic/Param.hs b/src/UI/Butcher/Monadic/Param.hs
index cb1b8a5..747224c 100644
--- a/src/UI/Butcher/Monadic/Param.hs
+++ b/src/UI/Butcher/Monadic/Param.hs
@@ -55,17 +55,20 @@ data Param p = Param
   , _param_suggestions :: Maybe [CompletionItem]
   }
 
+appendParam :: Param p -> Param p -> Param p
+appendParam (Param a1 b1 c1) (Param a2 b2 c2) = Param (a1 `f` a2)
+                                                      (b1 `mappend` b2)
+                                                      (c1 `mappend` c2)
+ where
+  f Nothing x = x
+  f x       _ = x
+
+instance Semigroup (Param p) where
+  (<>) = appendParam
+
 instance Monoid (Param p) where
   mempty = Param Nothing Nothing Nothing
-  mappend (Param a1 b1 c1)
-          (Param a2 b2 c2)
-    = Param
-          (a1 `f` a2)
-          (b1 `mappend` b2)
-          (c1 `mappend` c2)
-    where
-      f Nothing x = x
-      f x       _ = x
+  mappend = appendParam
 
 -- | Create a 'Param' with just a help text.
 paramHelpStr :: String -> Param p
diff --git a/src/UI/Butcher/Monadic/Pretty.hs b/src/UI/Butcher/Monadic/Pretty.hs
index adad104..8cf57b8 100644
--- a/src/UI/Butcher/Monadic/Pretty.hs
+++ b/src/UI/Butcher/Monadic/Pretty.hs
@@ -325,7 +325,7 @@ ppPartDescUsage = \case
       sgsDocs ->
         PP.parens $ PP.fcat $ PP.punctuate (PP.text "|") $ sgsDocs ++ [d]
   PartRedirect s _ -> Just $ PP.text s
-  PartMany p       -> rec p <&> (<> PP.text "+")
+  PartMany p       -> rec p <&> (PP.<> PP.text "+")
   PartWithHelp _ p -> rec p
   PartReorder ps ->
     let flags  = [ d | PartMany d <- ps ]
diff --git a/srcinc/prelude.inc b/srcinc/prelude.inc
index 6c36566..fb235a5 100644
--- a/srcinc/prelude.inc
+++ b/srcinc/prelude.inc
@@ -123,6 +123,7 @@ import Data.Void ( Void )
 import System.IO ( IO )
 import Data.Proxy ( Proxy(..) )
 import Data.Sequence ( Seq )
+import Data.Semigroup ( Semigroup(..) )
 
 import Data.Map ( Map )
 import Data.Set ( Set )
@@ -336,8 +337,7 @@ import Debug.Trace                        ( trace
 import Foreign.ForeignPtr                 ( ForeignPtr
                                           )
 
-import Data.Monoid                        ( (<>)
-                                          , mconcat
+import Data.Monoid                        ( mconcat
                                           , Monoid (..)
                                           )
 
@@ -388,6 +388,7 @@ import Data.Tree                          ( Tree(..)
 import Control.Monad.Trans.MultiRWS       ( MonadMultiReader(..)
                                           , MonadMultiWriter(..)
                                           , MonadMultiState(..)
+                                          , MonadMultiGet(..)
                                           )
 
 import Control.Monad.Trans.MultiReader    ( runMultiReaderTNil