diff --git a/.gitignore b/.gitignore
index a4ee41a..82f3a88 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,3 +17,6 @@ cabal.sandbox.config
 *.eventlog
 .stack-work/
 cabal.project.local
+cabal.project.local~
+.HTF/
+.ghc.environment.*
diff --git a/.travis.yml b/.travis.yml
index 273e33a..8a954f0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,96 +1,144 @@
-# This file has been generated -- see https://github.com/hvr/multi-ghc-travis
+# This Travis job script has been generated by a script via
+#
+#   make_travis_yml_2.hs '-o' '.travis.yml' 'hashmap.cabal'
+#
+# For more information, see https://github.com/hvr/multi-ghc-travis
+#
 language: c
 sudo: false
 
+git:
+  submodules: false  # whether to recursively clone submodules
+
 cache:
   directories:
-    - $HOME/.cabsnap
     - $HOME/.cabal/packages
+    - $HOME/.cabal/store
 
 before_cache:
   - rm -fv $HOME/.cabal/packages/hackage.haskell.org/build-reports.log
-  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/00-index.tar
+  # remove files that are regenerated by 'cabal update'
+  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/00-index.*
+  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/*.json
+  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/01-index.cache
+  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/01-index.tar
+  - rm -fv $HOME/.cabal/packages/hackage.haskell.org/01-index.tar.idx
+
+  - rm -fv $HOME/.cabal/packages/head.hackage
 
 matrix:
   include:
-    - env: CABALVER=1.24 GHCVER=7.0.4
-      compiler: ": #GHC 7.0.4"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-7.0.4], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=7.2.2
-      compiler: ": #GHC 7.2.2"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-7.2.2], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=7.4.2
-      compiler: ": #GHC 7.4.2"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-7.4.2], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=7.6.3
-      compiler: ": #GHC 7.6.3"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-7.6.3], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=7.8.4
-      compiler: ": #GHC 7.8.4"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-7.8.4], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=7.10.3
-      compiler: ": #GHC 7.10.3"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-7.10.3], sources: [hvr-ghc]}}
-    - env: CABALVER=1.24 GHCVER=8.0.2
-      compiler: ": #GHC 8.0.2"
-      addons: {apt: {packages: [cabal-install-1.24,ghc-8.0.2], sources: [hvr-ghc]}}
-    - env: CABALVER=2.0 GHCVER=8.2.2
-      compiler: ": #GHC 8.2.2"
-      addons: {apt: {packages: [cabal-install-2.0,ghc-8.2.2], sources: [hvr-ghc]}}
-    - env: CABALVER=head GHCVER=head
-      compiler: ": #GHC head"
-      addons: {apt: {packages: [cabal-install-head,ghc-head], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.0.4"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.0.4], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.2.2"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.2.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.4.2"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.4.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.6.3"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.6.3], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.8.4"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.8.4], sources: [hvr-ghc]}}
+    - compiler: "ghc-7.10.3"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-7.10.3], sources: [hvr-ghc]}}
+    - compiler: "ghc-8.0.2"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-8.0.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-8.2.2"
+    # env: TEST=--disable-tests BENCH=--disable-benchmarks
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-2.0,ghc-8.2.2], sources: [hvr-ghc]}}
+    - compiler: "ghc-8.4.1"
+      env: GHCHEAD=true
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-8.4.1], sources: [hvr-ghc]}}
+    - compiler: "ghc-head"
+      env: GHCHEAD=true
+      addons: {apt: {packages: [ghc-ppa-tools,cabal-install-head,ghc-head], sources: [hvr-ghc]}}
 
   allow_failures:
-    - env: CABALVER=head GHCVER=head
+    - compiler: "ghc-8.4.1"
+    - compiler: "ghc-head"
 
 before_install:
- - unset CC
- - export PATH=$HOME/.cabal/bin:/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
+  - HC=${CC}
+  - HCPKG=${HC/ghc/ghc-pkg}
+  - unset CC
+  - "PATH=~/.cabal/bin:/opt/ghc/bin:/opt/ghc-ppa-tools/bin:$PATH"
 
 install:
- - cabal --version
- - echo "$(ghc --version) [$(ghc --print-project-git-commit-id 2> /dev/null || echo '?')]"
- - if [ -f $HOME/.cabal/packages/hackage.haskell.org/00-index.tar.gz ];
-   then
-     zcat $HOME/.cabal/packages/hackage.haskell.org/00-index.tar.gz >
-          $HOME/.cabal/packages/hackage.haskell.org/00-index.tar;
-   fi
- - travis_retry cabal update -v
- - sed -i 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config
- - cabal install --only-dependencies --enable-tests --enable-benchmarks --dry -v > installplan.txt
- - sed -i -e '1,/^Resolving /d' installplan.txt; cat installplan.txt
-
-# check whether current requested install-plan matches cached package-db snapshot
- - if diff -u installplan.txt $HOME/.cabsnap/installplan.txt;
-   then
-     echo "cabal build-cache HIT";
-     rm -rfv .ghc;
-     cp -a $HOME/.cabsnap/ghc $HOME/.ghc;
-     cp -a $HOME/.cabsnap/lib $HOME/.cabsnap/share $HOME/.cabsnap/bin $HOME/.cabal/;
-   else
-     echo "cabal build-cache MISS";
-     rm -rf $HOME/.cabsnap;
-     mkdir -p $HOME/.ghc $HOME/.cabal/lib $HOME/.cabal/share $HOME/.cabal/bin;
-     cabal install -j --only-dependencies --enable-tests --enable-benchmarks;
-   fi
-
-# snapshot package-db on cache miss
- - if [ ! -d $HOME/.cabsnap ];
-   then
-      echo "snapshotting package-db to build-cache";
-      mkdir $HOME/.cabsnap;
-      cp -a $HOME/.ghc $HOME/.cabsnap/ghc;
-      cp -a $HOME/.cabal/lib $HOME/.cabal/share $HOME/.cabal/bin installplan.txt $HOME/.cabsnap/;
-   fi
+  - cabal --version
+  - echo "$(${HC} --version) [$(${HC} --print-project-git-commit-id 2> /dev/null || echo '?')]"
+  - BENCH=${BENCH---disable-benchmarks}
+  - TEST=${TEST---disable-tests}
+  - HADDOCK=${HADDOCK-true}
+  - INSTALLED=${INSTALLED-false}
+  - GHCHEAD=${GHCHEAD-false}
+  - travis_retry cabal update -v
+  - "sed -i.bak 's/^jobs:/-- jobs:/' ${HOME}/.cabal/config"
+  - rm -fv cabal.project.local
+  - "printf 'packages: \".\"\\n' > cabal.project"
+  # Overlay Hackage Package Index for GHC HEAD: https://github.com/hvr/head.hackage
+  - |
+    if $GHCHEAD; then
+      echo 'allow-newer: *:base, *:template-haskell' >> cabal.project
+      echo 'repository head.hackage' >> cabal.project
+      echo '   url: http://head.hackage.haskell.org/' >> cabal.project
+      echo '   secure: True' >> cabal.project
+      echo '   root-keys: 07c59cb65787dedfaef5bd5f987ceb5f7e5ebf88b904bbd4c5cbdeb2ff71b740' >> cabal.project
+      echo '              2e8555dde16ebd8df076f1a8ef13b8f14c66bad8eafefd7d9e37d0ed711821fb' >> cabal.project
+      echo '              8f79fd2389ab2967354407ec852cbe73f2e8635793ac446d09461ffb99527f6e' >> cabal.project
+      echo '   key-threshold: 3' >> cabal.project
+    fi
+  - cat cabal.project
+  - if $GHCHEAD; then cabal new-update head.hackage -v; fi
+  - if [ -f "./configure.ac" ]; then
+      (cd "."; autoreconf -i);
+    fi
+  - rm -f cabal.project.freeze
+  - cabal new-build -w ${HC} ${TEST} ${BENCH} --project-file="cabal.project" --dep -j2 all
+  # - cabal new-build -w ${HC} --disable-tests --disable-benchmarks --project-file="cabal.project" --dep -j2 all
+  - rm -rf "."/.ghc.environment.* "."/dist
+  - DISTDIR=$(mktemp -d /tmp/dist-test.XXXX)
 
 # Here starts the actual work to be performed for the package under test;
 # any command which exits with a non-zero exit code causes the build to fail.
 script:
- - if [ -f configure.ac ]; then autoreconf -i; fi
- - cabal configure --enable-tests --enable-benchmarks -v2  # -v2 provides useful information for debugging
- - cabal build -j1 --ghc-option=-Werror # this builds all libraries and executables (including tests/benchmarks)
- - cabal check
- - cabal sdist   # tests that a source-distribution can be generated
+  # test that source-distributions can be generated
+  - (cd "." && cabal sdist)
+  - mv "."/dist/hashmap-*.tar.gz ${DISTDIR}/
+  - cd ${DISTDIR} || false
+  - find . -maxdepth 1 -name '*.tar.gz' -exec tar -xvf '{}' \;
+  - "printf 'packages: hashmap-*/*.cabal\\n' > cabal.project"
+  # Overlay Hackage Package Index for GHC HEAD: https://github.com/hvr/head.hackage
+  - |
+    if $GHCHEAD; then
+      echo 'allow-newer: *:base, *:template-haskell' >> cabal.project
+      echo 'repository head.hackage' >> cabal.project
+      echo '   url: http://head.hackage.haskell.org/' >> cabal.project
+      echo '   secure: True' >> cabal.project
+      echo '   root-keys: 07c59cb65787dedfaef5bd5f987ceb5f7e5ebf88b904bbd4c5cbdeb2ff71b740' >> cabal.project
+      echo '              2e8555dde16ebd8df076f1a8ef13b8f14c66bad8eafefd7d9e37d0ed711821fb' >> cabal.project
+      echo '              8f79fd2389ab2967354407ec852cbe73f2e8635793ac446d09461ffb99527f6e' >> cabal.project
+      echo '   key-threshold: 3' >> cabal.project
+    fi
+  - cat cabal.project
+  # this builds all libraries and executables (without tests/benchmarks)
+  # - cabal new-build -w ${HC} --disable-tests --disable-benchmarks all
+
+  # Build with installed constraints for packages in global-db
+  - if $INSTALLED; then echo cabal new-build -w ${HC} --disable-tests --disable-benchmarks $(${HCPKG} list --global --simple-output --names-only | sed 's/\([a-zA-Z0-9-]\{1,\}\) */--constraint="\1 installed" /g') all | sh; else echo "Not building with installed constraints"; fi
+
+  # build & run tests, build benchmarks
+  - cabal new-build -w ${HC} ${TEST} ${BENCH} all
+  - if [ "x$TEST" = "x--enable-tests" ]; then cabal new-test -w ${HC} ${TEST} ${BENCH} all; fi
+
+  # haddock
+  - rm -rf ./dist-newstyle
+  - if $HADDOCK; then cabal new-haddock -w ${HC} ${TEST} ${BENCH} all; else echo "Skipping haddock generation";fi
 
+# REGENDATA ["-o",".travis.yml","hashmap.cabal"]
 # EOF
diff --git a/hashmap.cabal b/hashmap.cabal
index fa777f6..042226f 100644
--- a/hashmap.cabal
+++ b/hashmap.cabal
@@ -37,6 +37,7 @@ tested-with:         GHC == 7.0.4
                    , GHC == 7.10.3
                    , GHC == 8.0.2
                    , GHC == 8.2.2
+                   , GHC == 8.4.1
 
 source-repository head
   type: git