diff --git a/.hlint.yaml b/.hlint.yaml
--- a/.hlint.yaml
+++ b/.hlint.yaml
@@ -1,3 +1,5 @@
+- arguments: [-XCPP]
+
 - extensions:
   - default: false # all extension are banned by default
   - name:
@@ -9,11 +11,13 @@
     - GADTs
     - InstanceSigs
     - MultiParamTypeClasses
+    - PolyKinds
     - RankNTypes
+    - Safe
     - ScopedTypeVariables
     - Trustworthy
-    - TypeOperators
     - TypeFamilies
+    - TypeOperators
     - UndecidableInstances
 
 - functions:
@@ -51,7 +55,10 @@
 
 - ignore:
     name: Eta reduce
-    within: Data.Profunctor.Mapping
+    within:
+    - Data.Profunctor.Mapping
+    - Data.Profunctor.Choice
+    - Data.Profunctor.Strong
 
 - ignore:
     name: "Use tuple-section"
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
--- a/.travis.yml
+++ /dev/null
@@ -1,168 +0,0 @@
-# This Travis job script has been generated by a script via
-#
-#   haskell-ci '--output=.travis.yml' '--config=cabal.haskell-ci' 'cabal.project'
-#
-# For more information, see https://github.com/haskell-CI/haskell-ci
-#
-# version: 0.4
-#
-language: c
-dist: xenial
-git:
-  # whether to recursively clone submodules
-  submodules: false
-notifications:
-  irc:
-    channels:
-      - irc.freenode.org#haskell-lens
-    skip_join: true
-    template:
-      - "\"\\x0313profunctors\\x03/\\x0306%{branch}\\x03 \\x0314%{commit}\\x03 %{build_url} %{message}\""
-cache:
-  directories:
-    - $HOME/.cabal/packages
-    - $HOME/.cabal/store
-before_cache:
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/build-reports.log
-  # remove files that are regenerated by 'cabal update'
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/00-index.*
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/*.json
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.cache
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.tar
-  - rm -fv $CABALHOME/packages/hackage.haskell.org/01-index.tar.idx
-  - rm -rfv $CABALHOME/packages/head.hackage
-matrix:
-  include:
-    - compiler: ghc-8.8.1
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.8.1","cabal-install-3.0"]}}
-    - compiler: ghc-8.6.5
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.6.5","cabal-install-3.0"]}}
-    - compiler: ghc-8.4.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.4.4","cabal-install-3.0"]}}
-    - compiler: ghc-8.2.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.2.2","cabal-install-3.0"]}}
-    - compiler: ghc-8.0.2
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-8.0.2","cabal-install-3.0"]}}
-    - compiler: ghc-7.10.3
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.10.3","cabal-install-3.0"]}}
-    - compiler: ghc-7.8.4
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-7.8.4","cabal-install-3.0"]}}
-    - compiler: ghc-head
-      addons: {"apt":{"sources":["hvr-ghc"],"packages":["ghc-head","cabal-install-head"]}}
-  allow_failures:
-    - compiler: ghc-head
-before_install:
-  - HC=$(echo "/opt/$CC/bin/ghc" | sed 's/-/\//')
-  - WITHCOMPILER="-w $HC"
-  - HCPKG="$HC-pkg"
-  - unset CC
-  - CABAL=/opt/ghc/bin/cabal
-  - CABALHOME=$HOME/.cabal
-  - export PATH="$CABALHOME/bin:$PATH"
-  - TOP=$(pwd)
-  - "HCNUMVER=$(${HC} --numeric-version|perl -ne '/^(\\d+)\\.(\\d+)\\.(\\d+)(\\.(\\d+))?$/; print(10000 * $1 + 100 * $2 + ($3 == 0 ? $5 != 1 : $3))')"
-  - echo $HCNUMVER
-  - CABAL="$CABAL -vnormal+nowrap+markoutput"
-  - set -o pipefail
-  - |
-    echo 'function blue(s) { printf "\033[0;34m" s "\033[0m " }'           >> .colorful.awk
-    echo 'BEGIN { state = "output"; }'                                     >> .colorful.awk
-    echo '/^-----BEGIN CABAL OUTPUT-----$/ { state = "cabal" }'            >> .colorful.awk
-    echo '/^-----END CABAL OUTPUT-----$/ { state = "output" }'             >> .colorful.awk
-    echo '!/^(-----BEGIN CABAL OUTPUT-----|-----END CABAL OUTPUT-----)/ {' >> .colorful.awk
-    echo '  if (state == "cabal") {'                                       >> .colorful.awk
-    echo '    print blue($0)'                                              >> .colorful.awk
-    echo '  } else {'                                                      >> .colorful.awk
-    echo '    print $0'                                                    >> .colorful.awk
-    echo '  }'                                                             >> .colorful.awk
-    echo '}'                                                               >> .colorful.awk
-  - cat .colorful.awk
-  - |
-    color_cabal_output () {
-      awk -f $TOP/.colorful.awk
-    }
-  - echo text | color_cabal_output
-install:
-  - ${CABAL} --version
-  - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
-  - TEST=--enable-tests
-  - BENCH=--enable-benchmarks
-  - HEADHACKAGE=false
-  - if [ $HCNUMVER -gt 80801 ] ; then HEADHACKAGE=true ; fi
-  - rm -f $CABALHOME/config
-  - |
-    echo "verbose: normal +nowrap +markoutput"          >> $CABALHOME/config
-    echo "remote-build-reporting: anonymous"            >> $CABALHOME/config
-    echo "write-ghc-environment-files: always"          >> $CABALHOME/config
-    echo "remote-repo-cache: $CABALHOME/packages"       >> $CABALHOME/config
-    echo "logs-dir:          $CABALHOME/logs"           >> $CABALHOME/config
-    echo "world-file:        $CABALHOME/world"          >> $CABALHOME/config
-    echo "extra-prog-path:   $CABALHOME/bin"            >> $CABALHOME/config
-    echo "symlink-bindir:    $CABALHOME/bin"            >> $CABALHOME/config
-    echo "installdir:        $CABALHOME/bin"            >> $CABALHOME/config
-    echo "build-summary:     $CABALHOME/logs/build.log" >> $CABALHOME/config
-    echo "store-dir:         $CABALHOME/store"          >> $CABALHOME/config
-    echo "install-dirs user"                            >> $CABALHOME/config
-    echo "  prefix: $CABALHOME"                         >> $CABALHOME/config
-    echo "repository hackage.haskell.org"               >> $CABALHOME/config
-    echo "  url: http://hackage.haskell.org/"           >> $CABALHOME/config
-  - |
-    if $HEADHACKAGE; then
-    echo "allow-newer: $($HCPKG list --simple-output | sed -E 's/([a-zA-Z-]+)-[0-9.]+/*:\1/g')" >> $CABALHOME/config
-    echo "repository head.hackage.ghc.haskell.org"                                        >> $CABALHOME/config
-    echo "   url: https://ghc.gitlab.haskell.org/head.hackage/"                           >> $CABALHOME/config
-    echo "   secure: True"                                                                >> $CABALHOME/config
-    echo "   root-keys: 7541f32a4ccca4f97aea3b22f5e593ba2c0267546016b992dfadcd2fe944e55d" >> $CABALHOME/config
-    echo "              26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329" >> $CABALHOME/config
-    echo "              f76d08be13e9a61a377a85e2fb63f4c5435d40f8feb3e12eb05905edb8cdea89" >> $CABALHOME/config
-    echo "   key-threshold: 3"                                                            >> $CABALHOME/config
-    fi
-  - cat $CABALHOME/config
-  - rm -fv cabal.project cabal.project.local cabal.project.freeze
-  - travis_retry ${CABAL} v2-update -v
-  - if [ $HCNUMVER -ge 80800 ] && [ $HCNUMVER -lt 80802 ] ; then (cd /tmp && ${CABAL} v2-install $WITHCOMPILER -j2 hlint --constraint='hlint ==2.1.*' | color_cabal_output) ; fi
-  # Generate cabal.project
-  - rm -rf cabal.project cabal.project.local cabal.project.freeze
-  - touch cabal.project
-  - |
-    echo "packages: ." >> cabal.project
-  - |
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(profunctors)$' || true) | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
-  - cat cabal.project || true
-  - cat cabal.project.local || true
-  - if [ -f "./configure.ac" ]; then (cd "." && autoreconf -i); fi
-  - ${CABAL} v2-freeze $WITHCOMPILER ${TEST} ${BENCH} | color_cabal_output
-  - "cat cabal.project.freeze | sed -E 's/^(constraints: *| *)//' | sed 's/any.//'"
-  - rm  cabal.project.freeze
-  - ${CABAL} v2-build $WITHCOMPILER ${TEST} ${BENCH} --dep -j2 all | color_cabal_output
-script:
-  - DISTDIR=$(mktemp -d /tmp/dist-test.XXXX)
-  # Packaging...
-  - ${CABAL} v2-sdist all | color_cabal_output
-  # Unpacking...
-  - mv dist-newstyle/sdist/*.tar.gz ${DISTDIR}/
-  - cd ${DISTDIR} || false
-  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec tar -xvf '{}' \;
-  - find . -maxdepth 1 -type f -name '*.tar.gz' -exec rm       '{}' \;
-  - PKGDIR_profunctors="$(find . -maxdepth 1 -type d -regex '.*/profunctors-[0-9.]*')"
-  # Generate cabal.project
-  - rm -rf cabal.project cabal.project.local cabal.project.freeze
-  - touch cabal.project
-  - |
-    echo "packages: ${PKGDIR_profunctors}" >> cabal.project
-  - |
-  - "for pkg in $($HCPKG list --simple-output); do echo $pkg | sed 's/-[^-]*$//' | (grep -vE -- '^(profunctors)$' || true) | sed 's/^/constraints: /' | sed 's/$/ installed/' >> cabal.project.local; done"
-  - cat cabal.project || true
-  - cat cabal.project.local || true
-  # Building with tests and benchmarks...
-  # build & run tests, build benchmarks
-  - ${CABAL} v2-build $WITHCOMPILER ${TEST} ${BENCH} all | color_cabal_output
-  # HLint..
-  - if [ $HCNUMVER -ge 80800 ] && [ $HCNUMVER -lt 80802 ] ; then (cd ${PKGDIR_profunctors} && hlint src) ; fi
-  # cabal check...
-  - (cd ${PKGDIR_profunctors} && ${CABAL} -vnormal check)
-  # haddock...
-  - ${CABAL} v2-haddock $WITHCOMPILER ${TEST} ${BENCH} all | color_cabal_output
-
-# REGENDATA ["--output=.travis.yml","--config=cabal.haskell-ci","cabal.project"]
-# EOF
diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,25 @@
+5.6.3 [2025.06.17]
+------------------
+* Drop support for pre-8.0 versions of GHC.
+
+5.6.2 [2021.02.17]
+------------------
+* Add `Semigroup` and `Monoid` instances for `Forget`
+
+5.6.1 [2020.12.31]
+------------------
+* Add `Functor` instances for `PastroSum`, `CopastroSum`, `Environment`,
+  `FreeMapping`, `Pastro`, `Copastro`, `FreeTraversing`, and `Coyoneda`.
+* Explicitly mark modules as `Safe`.
+
+5.6 [2020.10.01]
+----------------
+* Enable the `PolyKinds` extension. The following datatypes now have
+  polymorphic kinds: `(:->)`, `Cayley`, `Procompose`, `Rift`,
+  `ProfunctorFunctor`, `Ran`, `Codensity`, `Prep`, `Coprep`, `Star`, `Costar`,
+  `WrappedArrow`, `Forget`.
+* Allow building with GHC 9.0.
+
 5.5.2 [2020.02.13]
 ------------------
 * Add `Cochoice`, `Costrong`, `Closed`, `Traversing`, and `Mapping` instances
diff --git a/README.markdown b/README.markdown
--- a/README.markdown
+++ b/README.markdown
@@ -1,7 +1,7 @@
 Profunctors
 ===========
 
-[![Hackage](https://img.shields.io/hackage/v/profunctors.svg)](https://hackage.haskell.org/package/profunctors) [![Build Status](https://secure.travis-ci.org/ekmett/profunctors.png?branch=master)](http://travis-ci.org/ekmett/profunctors)
+[![Hackage](https://img.shields.io/hackage/v/profunctors.svg)](https://hackage.haskell.org/package/profunctors) [![Build Status](https://github.com/ekmett/profunctors/workflows/Haskell-CI/badge.svg)](https://github.com/ekmett/profunctors/actions?query=workflow%3AHaskell-CI)
 
 Profunctors for Haskell.
 
diff --git a/profunctors.cabal b/profunctors.cabal
--- a/profunctors.cabal
+++ b/profunctors.cabal
@@ -1,6 +1,6 @@
 name:          profunctors
 category:      Control, Categories
-version:       5.5.2
+version:       5.6.3
 license:       BSD3
 cabal-version: >= 1.10
 license-file:  LICENSE
@@ -12,41 +12,42 @@
 copyright:     Copyright (C) 2011-2015 Edward A. Kmett
 synopsis:      Profunctors
 description:   Profunctors.
-tested-with:   GHC == 7.8.4
-             , GHC == 7.10.3
-             , GHC == 8.0.2
+tested-with:   GHC == 8.0.2
              , GHC == 8.2.2
              , GHC == 8.4.4
              , GHC == 8.6.5
-             , GHC == 8.8.1
+             , GHC == 8.8.4
+             , GHC == 8.10.7
+             , GHC == 9.0.2
+             , GHC == 9.2.8
+             , GHC == 9.4.8
+             , GHC == 9.6.6
+             , GHC == 9.8.4
+             , GHC == 9.10.1
+             , GHC == 9.12.2
 build-type:    Simple
 extra-source-files:
   .ghci
   .gitignore
   .hlint.yaml
-  .travis.yml
   .vim.custom
   README.markdown
   CHANGELOG.markdown
 
 source-repository head
   type: git
-  location: git://github.com/ekmett/profunctors.git
+  location: https://github.com/ekmett/profunctors.git
 
 library
   build-depends:
-    base                >= 4.7   && < 5,
-    base-orphans        >= 0.4   && < 0.9,
-    bifunctors          >= 5.2   && < 6,
-    comonad             >= 4     && < 6,
-    contravariant       >= 1     && < 2,
-    distributive        >= 0.4.4 && < 1,
-    tagged              >= 0.4.4 && < 1,
-    transformers        >= 0.2   && < 0.6
-
-  if !impl(ghc >= 8.0)
-    build-depends: semigroups >= 0.11 && < 0.20
-
+    base                >= 4.9     && < 5,
+    base-orphans        >= 0.8.4   && < 0.10,
+    bifunctors          >= 5.5.9   && < 6,
+    comonad             >= 5.0.8   && < 6,
+    contravariant       >= 1.5.3   && < 2,
+    distributive        >= 0.5.2   && < 1,
+    tagged              >= 0.8.6.1 && < 1,
+    transformers        >= 0.3     && < 0.7
   exposed-modules:
     Data.Profunctor
     Data.Profunctor.Adjunction
@@ -65,10 +66,15 @@
     Data.Profunctor.Unsafe
     Data.Profunctor.Yoneda
 
-  ghc-options:     -Wall -O2
+  ghc-options:     -Wall -O2 -Wno-trustworthy-safe
 
-  if impl(ghc>=8.0)
-    ghc-options: -Wno-trustworthy-safe
+  if impl(ghc >= 8.6)
+    ghc-options: -Wno-star-is-type
+
+  if impl(ghc >= 9.0)
+    -- these flags may abort compilation with GHC-8.10
+    -- https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3295
+    ghc-options: -Winferred-safe-imports -Wmissing-safe-haskell-mode
 
   hs-source-dirs:  src
 
diff --git a/src/Data/Profunctor.hs b/src/Data/Profunctor.hs
--- a/src/Data/Profunctor.hs
+++ b/src/Data/Profunctor.hs
@@ -1,6 +1,4 @@
-{-# LANGUAGE TypeOperators #-}
-{-# LANGUAGE RankNTypes #-}
-{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Copyright   :  (C) 2011-2015 Edward Kmett,
diff --git a/src/Data/Profunctor/Adjunction.hs b/src/Data/Profunctor/Adjunction.hs
--- a/src/Data/Profunctor/Adjunction.hs
+++ b/src/Data/Profunctor/Adjunction.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Copyright   :  (C) 2015 Edward Kmett
@@ -22,6 +23,8 @@
 -- 'unit' '.' 'counit' ≡ 'id'
 -- 'counit' '.' 'unit' ≡ 'id'
 -- @
+
+-- ProfunctorAdjunction :: ((Type -> Type -> Type) -> (Type -> Type -> Type)) -> ((Type -> Type -> Type) -> (Type -> Type -> Type)) -> Constraint
 class (ProfunctorFunctor f, ProfunctorFunctor u) => ProfunctorAdjunction f u | f -> u, u -> f where
   unit   :: Profunctor p => p :-> u (f p)
   counit :: Profunctor p => f (u p) :-> p
diff --git a/src/Data/Profunctor/Cayley.hs b/src/Data/Profunctor/Cayley.hs
--- a/src/Data/Profunctor/Cayley.hs
+++ b/src/Data/Profunctor/Cayley.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE Trustworthy #-}
 -----------------------------------------------------------------------------
@@ -23,7 +24,11 @@
 import Data.Profunctor.Unsafe
 import Prelude hiding ((.), id)
 
--- static arrows
+-- | Static arrows. Lifted by 'Applicative'.
+--
+-- 'Cayley' has a polymorphic kind since @5.6@.
+
+-- Cayley :: (k3 -> Type) -> (k1 -> k2 -> k3) -> (k1 -> k2 -> Type)
 newtype Cayley f p a b = Cayley { runCayley :: f (p a b) }
 
 instance Functor f => ProfunctorFunctor (Cayley f) where
diff --git a/src/Data/Profunctor/Choice.hs b/src/Data/Profunctor/Choice.hs
--- a/src/Data/Profunctor/Choice.hs
+++ b/src/Data/Profunctor/Choice.hs
@@ -1,8 +1,8 @@
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Copyright   :  (C) 2014-2015 Edward Kmett
@@ -42,12 +42,7 @@
 import Data.Profunctor.Types
 import Data.Profunctor.Unsafe
 import Data.Tagged
-#if __GLASGOW_HASKELL__ < 710
-import Data.Traversable
-import Prelude hiding (id,(.),sequence)
-#else
 import Prelude hiding (id,(.))
-#endif
 
 ------------------------------------------------------------------------------
 -- Choice
@@ -197,7 +192,7 @@
   promap f (TambaraSum p) = TambaraSum (f p)
 
 instance ProfunctorComonad TambaraSum where
-  proextract (TambaraSum p)   = dimap Left (\(Left a) -> a) p
+  proextract (TambaraSum p)   = dimap Left fromEither p
   produplicate (TambaraSum p) = TambaraSum (TambaraSum $ dimap hither yon p) where
     hither :: Either (Either a b) c -> Either a (Either b c)
     hither (Left (Left x))   = Left x
@@ -214,7 +209,7 @@
   {-# INLINE dimap #-}
 
 instance Profunctor p => Choice (TambaraSum p) where
-  left' = runTambaraSum . produplicate
+  left' p = runTambaraSum $ produplicate p
   {-# INLINE left' #-}
 
 instance Category p => Category (TambaraSum p) where
@@ -238,8 +233,11 @@
 -- 'untambaraSum' '.' 'tambaraSum' ≡ 'id'
 -- @
 untambaraSum :: Profunctor q => (p :-> TambaraSum q) -> p :-> q
-untambaraSum f p = dimap Left (\(Left a) -> a) $ runTambaraSum $ f p
+untambaraSum f p = dimap Left fromEither $ runTambaraSum $ f p
 
+fromEither :: Either a a -> a
+fromEither = either id id
+
 ----------------------------------------------------------------------------
 -- * PastroSum
 ----------------------------------------------------------------------------
@@ -250,6 +248,9 @@
 data PastroSum p a b where
   PastroSum :: (Either y z -> b) -> p x y -> (a -> Either x z) -> PastroSum p a b
 
+instance Functor (PastroSum p a) where
+  fmap f (PastroSum l m r) = PastroSum (f . l) m r
+
 instance Profunctor (PastroSum p) where
   dimap f g (PastroSum l m r) = PastroSum (g . l) m (r . f)
   lmap f (PastroSum l m r) = PastroSum l m (r . f)
@@ -265,7 +266,7 @@
   promap f (PastroSum l m r) = PastroSum l (f m) r
 
 instance ProfunctorMonad PastroSum where
-  proreturn p = PastroSum (\(Left a)-> a) p Left
+  proreturn p = PastroSum fromEither p Left
   projoin (PastroSum l (PastroSum m n o) q) = PastroSum lm n oq where
     oq a = case q a of
       Left b -> Left <$> o b
@@ -401,7 +402,7 @@
 -- 'uncotambaraSum' '.' 'cotambaraSum' ≡ 'id'
 -- @
 cotambaraSum :: Cochoice p => (p :-> q) -> p :-> CotambaraSum q
-cotambaraSum = CotambaraSum
+cotambaraSum f = CotambaraSum f
 
 -- |
 -- @
@@ -419,6 +420,9 @@
 --
 -- 'CopastroSum' freely constructs costrength with respect to 'Either' (aka 'Choice')
 newtype CopastroSum p a b = CopastroSum { runCopastroSum :: forall r. Cochoice r => (forall x y. p x y -> r x y) -> r a b }
+
+instance Functor (CopastroSum p a) where
+  fmap f (CopastroSum h) = CopastroSum $ \ n -> rmap f (h n)
 
 instance Profunctor (CopastroSum p) where
   dimap f g (CopastroSum h) = CopastroSum $ \ n -> dimap f g (h n)
diff --git a/src/Data/Profunctor/Closed.hs b/src/Data/Profunctor/Closed.hs
--- a/src/Data/Profunctor/Closed.hs
+++ b/src/Data/Profunctor/Closed.hs
@@ -120,11 +120,11 @@
   promap f (Closure p) = Closure (f p)
 
 instance ProfunctorComonad Closure where
-  proextract = dimap const ($ ()) . runClosure
+  proextract p = dimap const ($ ()) $ runClosure p
   produplicate (Closure p) = Closure $ Closure $ dimap uncurry curry p
 
 instance Profunctor p => Closed (Closure p) where
-  closed = runClosure . produplicate
+  closed p = runClosure $ produplicate p
 
 instance Strong p => Strong (Closure p) where
   first' (Closure p) = Closure $ dimap hither yon $ first' p
@@ -194,6 +194,9 @@
 
 data Environment p a b where
   Environment :: ((z -> y) -> b) -> p x y -> (a -> z -> x) -> Environment p a b
+
+instance Functor (Environment p a) where
+  fmap f (Environment l m r) = Environment (f . l) m r
 
 instance Profunctor (Environment p) where
   dimap f g (Environment l m r) = Environment (g . l) m (r . f)
diff --git a/src/Data/Profunctor/Composition.hs b/src/Data/Profunctor/Composition.hs
--- a/src/Data/Profunctor/Composition.hs
+++ b/src/Data/Profunctor/Composition.hs
@@ -1,9 +1,11 @@
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Profunctor.Composition
@@ -60,6 +62,10 @@
 -- see Dan Piponi's article:
 --
 -- <http://blog.sigfpe.com/2011/07/profunctors-in-haskell.html>
+--
+-- 'Procompose' has a polymorphic kind since @5.6@.
+
+-- Procompose :: (k1 -> k2 -> Type) -> (k3 -> k1 -> Type) -> (k3 -> k2 -> Type)
 data Procompose p q d c where
   Procompose :: p x c -> q d x -> Procompose p q d c
 
@@ -237,7 +243,15 @@
 -- * Rift
 ----------------------------------------------------------------------------
 
--- | This represents the right Kan lift of a 'Profunctor' @q@ along a 'Profunctor' @p@ in a limited version of the 2-category of Profunctors where the only object is the category Hask, 1-morphisms are profunctors composed and compose with Profunctor composition, and 2-morphisms are just natural transformations.
+-- | This represents the right Kan lift of a 'Profunctor' @q@ along a
+-- 'Profunctor' @p@ in a limited version of the 2-category of Profunctors where
+-- the only object is the category Hask, 1-morphisms are profunctors composed
+-- and compose with Profunctor composition, and 2-morphisms are just natural
+-- transformations.
+--
+-- 'Rift' has a polymorphic kind since @5.6@.
+
+-- Rift :: (k3 -> k2 -> Type) -> (k1 -> k2 -> Type) -> (k1 -> k3 -> Type)
 newtype Rift p q a b = Rift { runRift :: forall x. p b x -> q a x }
 
 instance ProfunctorFunctor (Rift p) where
diff --git a/src/Data/Profunctor/Mapping.hs b/src/Data/Profunctor/Mapping.hs
--- a/src/Data/Profunctor/Mapping.hs
+++ b/src/Data/Profunctor/Mapping.hs
@@ -1,7 +1,7 @@
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Copyright   :  (C) 2015-2018 Edward Kmett
@@ -35,9 +35,6 @@
 import Data.Profunctor.Traversing
 import Data.Profunctor.Types
 import Data.Profunctor.Unsafe
-#if __GLASGOW_HASKELL__ < 710
-import Control.Applicative
-#endif
 
 class (Traversing p, Closed p) => Mapping p where
   -- | Laws:
@@ -67,21 +64,7 @@
 
 instance (Monad m, Distributive m) => Mapping (Kleisli m) where
   map' (Kleisli f) = Kleisli (collect f)
-#if __GLASGOW_HASKELL__ >= 710
   roam f = Kleisli #. genMap f .# runKleisli
-#else
-  -- We could actually use this implementation everywhere, but it's kind of a
-  -- warty mess, and there have been rumblings of WrappedMonad deprecation.
-  -- If/when GHC 7.8 moves out of the support window, this will vanish in a
-  -- puff of cleanup.
-  roam f = (Kleisli . (unwrapMonad .)) #. genMapW f .# ((WrapMonad .) . runKleisli)
-    where
-      genMapW
-        :: (Monad m, Distributive m)
-        => ((a -> b) -> s -> t)
-        -> (a -> WrappedMonad m b) -> s -> WrappedMonad m t
-      genMapW abst amb s = WrapMonad $ (\ab -> abst ab s) <$> distribute (unwrapMonad #. amb)
-#endif
 
 genMap :: Distributive f => ((a -> b) -> s -> t) -> (a -> f b) -> s -> f t
 genMap abst afb s = fmap (\ab -> abst ab s) (distribute afb)
@@ -140,6 +123,9 @@
 -- | @FreeMapping -| CofreeMapping@
 data FreeMapping p a b where
   FreeMapping :: Functor f => (f y -> b) -> p x y -> (a -> f x) -> FreeMapping p a b
+
+instance Functor (FreeMapping p a) where
+  fmap f (FreeMapping l m r) = FreeMapping (f . l) m r
 
 instance Profunctor (FreeMapping p) where
   lmap f (FreeMapping l m r) = FreeMapping l m (r . f)
diff --git a/src/Data/Profunctor/Monad.hs b/src/Data/Profunctor/Monad.hs
--- a/src/Data/Profunctor/Monad.hs
+++ b/src/Data/Profunctor/Monad.hs
@@ -1,6 +1,7 @@
-{-# LANGUAGE CPP #-}
+{-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Copyright   :  (C) 2014-2015 Edward Kmett
@@ -19,6 +20,9 @@
 import Data.Bifunctor.Sum
 import Data.Profunctor.Types
 
+-- | 'ProfunctorFunctor' has a polymorphic kind since @5.6@.
+
+-- ProfunctorFunctor :: ((Type -> Type -> Type) -> (k1 -> k2 -> Type)) -> Constraint
 class ProfunctorFunctor t where
   -- | Laws:
   --
@@ -26,7 +30,7 @@
   -- 'promap' f '.' 'promap' g ≡ 'promap' (f '.' g)
   -- 'promap' 'id' ≡ 'id'
   -- @
-  promap    :: Profunctor p => (p :-> q) -> t p :-> t q
+  promap :: Profunctor p => (p :-> q) -> t p :-> t q
 
 instance Functor f => ProfunctorFunctor (Tannen f) where
   promap f (Tannen g) = Tannen (fmap f g)
@@ -46,15 +50,13 @@
 -- 'projoin' '.' 'promap' 'proreturn' ≡ 'id'
 -- 'projoin' '.' 'projoin' ≡ 'projoin' '.' 'promap' 'projoin'
 -- @
+
+-- ProfunctorMonad :: ((Type -> Type -> Type) -> (Type -> Type -> Type)) -> Constraint
 class ProfunctorFunctor t => ProfunctorMonad t where
   proreturn :: Profunctor p => p :-> t p
   projoin   :: Profunctor p => t (t p) :-> t p
 
-#if __GLASGOW_HASKELL__ < 710
-instance (Functor f, Monad f) => ProfunctorMonad (Tannen f) where
-#else
 instance Monad f => ProfunctorMonad (Tannen f) where
-#endif
   proreturn = Tannen . return
   projoin (Tannen m) = Tannen $ m >>= runTannen
 
@@ -71,6 +73,8 @@
 -- 'promap' 'proextract' '.' 'produplicate' ≡ 'id'
 -- 'produplicate' '.' 'produplicate' ≡ 'promap' 'produplicate' '.' 'produplicate'
 -- @
+
+-- ProfunctorComonad :: ((Type -> Type -> Type) -> (Type -> Type -> Type)) -> Constraint
 class ProfunctorFunctor t => ProfunctorComonad t where
   proextract :: Profunctor p => t p :-> p
   produplicate :: Profunctor p => t p :-> t (t p)
diff --git a/src/Data/Profunctor/Ran.hs b/src/Data/Profunctor/Ran.hs
--- a/src/Data/Profunctor/Ran.hs
+++ b/src/Data/Profunctor/Ran.hs
@@ -1,6 +1,8 @@
+{-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Copyright   :  (C) 2013-2015 Edward Kmett and Dan Doel
@@ -32,7 +34,15 @@
 -- * Ran
 --------------------------------------------------------------------------------
 
--- | This represents the right Kan extension of a 'Profunctor' @q@ along a 'Profunctor' @p@ in a limited version of the 2-category of Profunctors where the only object is the category Hask, 1-morphisms are profunctors composed and compose with Profunctor composition, and 2-morphisms are just natural transformations.
+-- | This represents the right Kan extension of a 'Profunctor' @q@ along a
+-- 'Profunctor' @p@ in a limited version of the 2-category of Profunctors where
+-- the only object is the category Hask, 1-morphisms are profunctors composed
+-- and compose with Profunctor composition, and 2-morphisms are just natural
+-- transformations.
+--
+-- 'Ran' has a polymorphic kind since @5.6@.
+
+-- Ran :: (k1 -> k2 -> Type) -> (k1 -> k3 -> Type) -> (k2 -> k3 -> Type)
 newtype Ran p q a b = Ran { runRan :: forall x. p x a -> q x b }
 
 instance ProfunctorFunctor (Ran p) where
@@ -88,7 +98,13 @@
 -- * Codensity
 --------------------------------------------------------------------------------
 
--- | This represents the right Kan extension of a 'Profunctor' @p@ along itself. This provides a generalization of the \"difference list\" trick to profunctors.
+-- | This represents the right Kan extension of a 'Profunctor' @p@ along
+-- itself. This provides a generalization of the \"difference list\" trick to
+-- profunctors.
+--
+-- 'Codensity' has a polymorphic kind since @5.6@.
+
+-- Codensity :: (k1 -> k2 -> Type) -> (k2 -> k2 -> Type)
 newtype Codensity p a b = Codensity { runCodensity :: forall x. p x a -> p x b }
 
 instance Profunctor p => Profunctor (Codensity p) where
diff --git a/src/Data/Profunctor/Rep.hs b/src/Data/Profunctor/Rep.hs
--- a/src/Data/Profunctor/Rep.hs
+++ b/src/Data/Profunctor/Rep.hs
@@ -1,11 +1,13 @@
-{-# LANGUAGE RankNTypes #-}
-{-# LANGUAGE UndecidableInstances #-}
-{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
-{-# LANGUAGE GADTs #-}
-{-# LANGUAGE CPP #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Profunctor.Rep
@@ -178,6 +180,10 @@
 --
 -- This gives rise to a monad in @Prof@, @('Star'.'Prep')@, and
 -- a comonad in @[Hask,Hask]@ @('Prep'.'Star')@
+--
+-- 'Prep' has a polymorphic kind since @5.6@.
+
+-- Prep :: (Type -> k -> Type) -> (k -> Type)
 data Prep p a where
   Prep :: x -> p x a -> Prep p a
 
@@ -190,7 +196,9 @@
     go (xf',xa') = sieve pf xf' <*> sieve pa xa'
 
 instance (Monad (Rep p), Representable p) => Monad (Prep p) where
+#if !(MIN_VERSION_base(4,11,0))
   return a = Prep () $ tabulate $ const $ return a
+#endif
   Prep xa pa >>= f = Prep xa $ tabulate $ sieve pa >=> \a -> case f a of
     Prep xb pb -> sieve pb xb
 
@@ -210,6 +218,9 @@
 -- * Coprep
 --------------------------------------------------------------------------------
 
+-- | 'Prep' has a polymorphic kind since @5.6@.
+
+-- Coprep :: (k -> Type -> Type) -> (k -> Type)
 newtype Coprep p a = Coprep { runCoprep :: forall r. p a r -> r }
 
 instance Profunctor p => Functor (Coprep p) where
diff --git a/src/Data/Profunctor/Strong.hs b/src/Data/Profunctor/Strong.hs
--- a/src/Data/Profunctor/Strong.hs
+++ b/src/Data/Profunctor/Strong.hs
@@ -3,6 +3,7 @@
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE Safe #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -185,7 +186,7 @@
     yon    ~(x,~(y,z)) = ((x,y),z)
 
 instance Profunctor p => Strong (Tambara p) where
-  first' = runTambara . produplicate
+  first' p = runTambara $ produplicate p
   {-# INLINE first' #-}
 
 instance Category p => Category (Tambara p) where
@@ -272,6 +273,9 @@
 data Pastro p a b where
   Pastro :: ((y, z) -> b) -> p x y -> (a -> (x, z)) -> Pastro p a b
 
+instance Functor (Pastro p a) where
+  fmap f (Pastro l m r) = Pastro (f . l) m r
+
 instance Profunctor (Pastro p) where
   dimap f g (Pastro l m r) = Pastro (g . l) m (r . f)
   lmap f (Pastro l m r) = Pastro l m (r . f)
@@ -425,7 +429,7 @@
 -- 'uncotambara' '.' 'cotambara' ≡ 'id'
 -- @
 cotambara :: Costrong p => (p :-> q) -> p :-> Cotambara q
-cotambara = Cotambara
+cotambara f = Cotambara f
 
 -- |
 -- @
@@ -443,6 +447,9 @@
 --
 -- Copastro freely constructs costrength
 newtype Copastro p a b = Copastro { runCopastro :: forall r. Costrong r => (forall x y. p x y -> r x y) -> r a b }
+
+instance Functor (Copastro p a) where
+  fmap f (Copastro h) = Copastro $ \ n -> rmap f (h n)
 
 instance Profunctor (Copastro p) where
   dimap f g (Copastro h) = Copastro $ \ n -> dimap f g (h n)
diff --git a/src/Data/Profunctor/Traversing.hs b/src/Data/Profunctor/Traversing.hs
--- a/src/Data/Profunctor/Traversing.hs
+++ b/src/Data/Profunctor/Traversing.hs
@@ -1,7 +1,7 @@
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE Safe #-}
 module Data.Profunctor.Traversing
   ( Traversing(..)
   , CofreeTraversing(..)
@@ -32,12 +32,6 @@
 import Data.Traversable
 import Data.Tuple (swap)
 
-#if __GLASGOW_HASKELL__ < 710
-import Data.Monoid (Monoid)
-import Data.Foldable
-import Prelude hiding (mapM)
-#endif
-
 firstTraversing :: Traversing p => p a b -> p (a, c) (b, c)
 firstTraversing = dimap swap swap . traverse'
 
@@ -167,6 +161,9 @@
 -- | @FreeTraversing -| CofreeTraversing@
 data FreeTraversing p a b where
   FreeTraversing :: Traversable f => (f y -> b) -> p x y -> (a -> f x) -> FreeTraversing p a b
+
+instance Functor (FreeTraversing p a) where
+  fmap f (FreeTraversing l m r) = FreeTraversing (f . l) m r
 
 instance Profunctor (FreeTraversing p) where
   lmap f (FreeTraversing l m r) = FreeTraversing l m (r . f)
diff --git a/src/Data/Profunctor/Types.hs b/src/Data/Profunctor/Types.hs
--- a/src/Data/Profunctor/Types.hs
+++ b/src/Data/Profunctor/Types.hs
@@ -1,7 +1,8 @@
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeOperators #-}
 
 {-# LANGUAGE Trustworthy #-}
 
@@ -40,12 +41,19 @@
 import Data.Distributive
 import Data.Foldable
 import Data.Functor.Contravariant
-import Data.Monoid hiding (Product)
 import Data.Profunctor.Unsafe
 import Data.Traversable
 import Prelude hiding (id,(.))
 
+#if !(MIN_VERSION_base(4,11,0))
+import Data.Semigroup (Semigroup(..))
+#endif
+
 infixr 0 :->
+
+-- | (':->') has a polymorphic kind since @5.6@.
+
+-- (:->) :: forall k1 k2. (k1 -> k2 -> Type) -> (k1 -> k2 -> Type) -> Type
 type p :-> q = forall a b. p a b -> q a b
 
 ------------------------------------------------------------------------------
@@ -53,6 +61,10 @@
 ------------------------------------------------------------------------------
 
 -- | Lift a 'Functor' into a 'Profunctor' (forwards).
+--
+-- 'Star' has a polymorphic kind since @5.6@.
+
+-- Star :: (k -> Type) -> (Type -> k -> Type)
 newtype Star f d c = Star { runStar :: d -> f c }
 
 instance Functor f => Profunctor (Star f) where
@@ -81,9 +93,6 @@
   Star f <|> Star g = Star $ \a -> f a <|> g a
 
 instance Monad f => Monad (Star f a) where
-#if __GLASGOW_HASKELL__ < 710
-  return a = Star $ \_ -> return a
-#endif
   Star m >>= f = Star $ \ e -> do
     a <- m e
     runStar (f a) e
@@ -108,6 +117,10 @@
 ------------------------------------------------------------------------------
 
 -- | Lift a 'Functor' into a 'Profunctor' (backwards).
+--
+-- 'Costar' has a polymorphic kind since @5.6@.
+
+-- Costar :: (k -> Type) -> k -> Type -> Type
 newtype Costar f d c = Costar { runCostar :: f d -> c }
 
 instance Functor f => Profunctor (Costar f) where
@@ -145,6 +158,10 @@
 ------------------------------------------------------------------------------
 
 -- | Wrap an arrow for use as a 'Profunctor'.
+--
+-- 'WrappedArrow' has a polymorphic kind since @5.6@.
+
+-- WrappedArrow :: (k1 -> k2 -> Type) -> (k1 -> k2 -> Type)
 newtype WrappedArrow p a b = WrapArrow { unwrapArrow :: p a b }
 
 instance Category p => Category (WrappedArrow p) where
@@ -198,6 +215,9 @@
 -- Forget
 ------------------------------------------------------------------------------
 
+-- | 'Forget' has a polymorphic kind since @5.6@.
+
+-- Forget :: Type -> Type -> k -> Type
 newtype Forget r a b = Forget { runForget :: a -> r }
 
 instance Profunctor (Forget r) where
@@ -223,3 +243,21 @@
 instance Contravariant (Forget r a) where
   contramap _ (Forget k) = Forget k
   {-# INLINE contramap #-}
+
+-- | Via @Semigroup r => (a -> r)@
+--
+-- @since 5.6.2
+instance Semigroup r => Semigroup (Forget r a b) where
+  Forget f <> Forget g = Forget (f <> g)
+  {-# INLINE (<>) #-}
+
+-- | Via @Monoid r => (a -> r)@
+--
+-- @since 5.6.2
+instance Monoid r => Monoid (Forget r a b) where
+  mempty = Forget mempty
+  {-# INLINE mempty #-}
+#if !(MIN_VERSION_base(4,11,0))
+  mappend (Forget f) (Forget g) = Forget (mappend f g)
+  {-# INLINE mappend #-}
+#endif
diff --git a/src/Data/Profunctor/Unsafe.hs b/src/Data/Profunctor/Unsafe.hs
--- a/src/Data/Profunctor/Unsafe.hs
+++ b/src/Data/Profunctor/Unsafe.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE Trustworthy #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 -----------------------------------------------------------------------------
@@ -41,9 +40,6 @@
 import Data.Bifunctor.Sum (Sum(..))
 import Data.Bifunctor.Tannen (Tannen(..))
 import Data.Coerce (Coercible, coerce)
-#if __GLASGOW_HASKELL__ < 710
-import Data.Functor
-#endif
 import Data.Functor.Contravariant (Contravariant(..))
 import Data.Tagged
 import Prelude hiding (id,(.))
diff --git a/src/Data/Profunctor/Yoneda.hs b/src/Data/Profunctor/Yoneda.hs
--- a/src/Data/Profunctor/Yoneda.hs
+++ b/src/Data/Profunctor/Yoneda.hs
@@ -2,7 +2,6 @@
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE Trustworthy #-}
 -----------------------------------------------------------------------------
 -- |
@@ -155,6 +154,9 @@
 -- @
 joinCoyoneda :: Coyoneda (Coyoneda p) a b -> Coyoneda p a b
 joinCoyoneda (Coyoneda l r p) = dimap l r p
+
+instance Functor (Coyoneda p a) where
+  fmap f (Coyoneda l r' p) = Coyoneda l (f . r') p
 
 instance Profunctor (Coyoneda p) where
   dimap l r (Coyoneda l' r' p) = Coyoneda (l' . l) (r . r') p