diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,128 @@
+# Builds and tests this Haskell project on "GitHub Actions"
+#
+# 2021  Rudy Matela
+#
+# some docs: https://github.com/haskell/actions/tree/main/setup
+name: build
+on: [push]
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    steps:
+
+      - name: Cache ~/.cabal/packages
+        uses: actions/cache@v2
+        with:
+          path: ~/.cabal/packages
+          key:          v1-${{ runner.os }}-cabal-packages-${{ hashFiles('hello.cabal') }}
+          restore-keys: v1-${{ runner.os }}-cabal-packages-
+
+      - name: Cache ~/.cabal and ~/.ghc
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cabal
+            !~/.cabal/packages
+            ~/.ghc
+          key:          v1-${{ runner.os }}-cabal-ghc-latest-${{ hashFiles('hello.cabal') }}
+          restore-keys: v1-${{ runner.os }}-cabal-ghc-latest-
+
+      - run: du -hd3 ~/.cabal ~/.ghc || true
+
+      - run: haddock --version || sudo apt-get install ghc-haddock
+      - run: ghc     --version
+      - run: cabal   --version
+      - run: haddock --version
+      - run: ghc-pkg list
+
+      - name: Check out repository
+        uses: actions/checkout@v2
+
+      - run: cabal update
+      - run: make install-dependencies
+
+      - run: make
+      - run: make test
+      - run: make haddock
+      - run: make test-sdist
+      - run: make test-via-cabal
+
+
+  test-with-ghc:
+    strategy:
+      matrix:
+        ghc:
+          - '9.0'
+          - '8.10'
+          - '8.8'
+          - '8.6'
+          - '8.4'
+          - '8.2'
+          - '8.0'
+          - '7.10'
+          - '7.8'
+    runs-on: ubuntu-latest
+    needs: build-and-test
+    container: haskell:${{ matrix.ghc }}
+    steps:
+      - name: Cache ~/.cabal/packages
+        uses: actions/cache@v2
+        with:
+          path: ~/.cabal/packages
+          key:          v1-${{ runner.os }}-cabal-packages-${{ hashFiles('hello.cabal') }}
+          restore-keys: v1-${{ runner.os }}-cabal-packages-
+
+      - name: Cache ~/.cabal and ~/.ghc
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cabal
+            !~/.cabal/packages
+            ~/.ghc
+          key:          v1-${{ runner.os }}-cabal-ghc-${{ matrix.ghc }}-${{ hashFiles('hello.cabal') }}
+          restore-keys: v1-${{ runner.os }}-cabal-ghc-${{ matrix.ghc }}-
+
+      - run: du -hd3 ~/.cabal ~/.ghc || true
+
+      - run: make --version || rm /etc/apt/sources.list.d/*.list # faster update
+      - run: make --version || apt-get update
+      - run: make --version || apt-get install make
+
+      - run: ghc     --version
+      - run: cabal   --version
+      - run: haddock --version
+      - run: ghc-pkg list
+
+      - name: Check out repository
+        uses: actions/checkout@v2
+
+      - run: cabal update
+      - run: make install-dependencies
+
+      - run: make
+      - run: make test
+      - run: make haddock
+      - run: make test-sdist
+      - run: make test-via-cabal
+
+  test-with-stack:
+    runs-on: ubuntu-latest
+    needs: build-and-test
+    steps:
+      - name: Setup Haskell's GHC and Cabal as required by current Stackage LTS
+        uses: haskell/actions/setup@v1
+        with: # lts-17.9
+          ghc-version: '8.10.4'
+          cabal-version: '3.2'
+
+      - uses: actions/cache@v2
+        with:
+          path: ~/.stack
+          key:          v1-${{ runner.os }}-stack-${{ hashFiles('stack.yaml') }}
+          restore-keys: v1-${{ runner.os }}-stack-
+
+      - run: stack --version
+
+      - name: Check out repository
+        uses: actions/checkout@v2
+      - run: make test-via-stack
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
--- a/.travis.yml
+++ /dev/null
@@ -1,90 +0,0 @@
-# .travis.yml file for Extrapolate
-#
-# Copyright:   (c) 2017-2020 Rudy Matela
-# License:     3-Clause BSD  (see the file LICENSE)
-# Maintainer:  Rudy Matela <rudy@matela.com.br>
-
-language: c  # not really
-
-notifications:
-  email:
-    on_failure: change
-
-sudo: false
-
-cache:
-  directories:
-  - $HOME/.ghc
-  - $HOME/.cabal
-  - $HOME/.stack
-
-before_install:
-- export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
-- ghc --version
-- cabal --version
-- haddock --version
-- du -hd3 ~/.cabal ~/.ghc || true
-- du -hd4 ~/.stack || true
-- rm -f ~/.cabal/config && cabal update
-# Download and unpack the stack executable
-# "Once Travis whitelists the stack.dev files," simply include stack in the
-# addons section. -- https://docs.haskellstack.org/en/stable/travis_ci/
-- mkdir -p ~/.local/bin
-- export PATH=$HOME/.local/bin:$PATH
-- travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
-- stack config set system-ghc --global true
-- stack --version
-- cabal install leancheck express speculate || cabal v1-install leancheck express speculate
-
-script:
-- make && make test
-- make haddock
-- make test-sdist
-- cabal test --ghc-option=-O0
-- stack --resolver $STACKVER --no-terminal --skip-ghc-check test --ghc-options=-O0
-
-matrix:
-  allow_failures:
-  - ghc: 'head'
-  include:
-  - ghc: 'head'
-    env:                   GHCVER=head         CABALVER=head   STACKVER=nightly-2020-03-28
-    addons: {apt: {packages: [ghc-head,   cabal-install-head], sources: hvr-ghc}}
-  - ghc: '8.10'
-    env:                   GHCVER=8.10.1       CABALVER=3.2    STACKVER=nightly-2020-03-28
-    addons: {apt: {packages: [ghc-8.10.1, cabal-install-3.2],  sources: hvr-ghc}}
-  - ghc: '8.8'
-    env:                   GHCVER=8.8.3        CABALVER=3.0    STACKVER=lts-15.6
-    addons: {apt: {packages: [ghc-8.8.3,  cabal-install-3.0],  sources: hvr-ghc}}
-  - ghc: '8.6'
-    env:                   GHCVER=8.6.5        CABALVER=2.4    STACKVER=lts-14.27
-    addons: {apt: {packages: [ghc-8.6.5,  cabal-install-2.4],  sources: hvr-ghc}}
-  - ghc: '8.4'
-    env:                   GHCVER=8.4.4        CABALVER=2.2    STACKVER=lts-12.26
-    addons: {apt: {packages: [ghc-8.4.4,  cabal-install-2.2],  sources: hvr-ghc}}
-  - ghc: '8.2'
-    env:                   GHCVER=8.2.2        CABALVER=2.0    STACKVER=lts-11.22
-    addons: {apt: {packages: [ghc-8.2.2,  cabal-install-2.0],  sources: hvr-ghc}}
-  - ghc: '8.0'
-    env:                   GHCVER=8.0.2        CABALVER=1.24   STACKVER=lts-9.21
-    addons: {apt: {packages: [ghc-8.0.2,  cabal-install-1.24], sources: hvr-ghc}}
-  - ghc: '7.10'
-    env:                   GHCVER=7.10.3       CABALVER=1.22   STACKVER=lts-6.35
-    addons: {apt: {packages: [ghc-7.10.3, cabal-install-1.22], sources: hvr-ghc}}
-  # we only support stack with GHC >= 7.10
-  - ghc: '7.8'
-    env:                   GHCVER=7.8.4        CABALVER=1.18
-    addons: {apt: {packages: [ghc-7.8.4,  cabal-install-1.18], sources: hvr-ghc}}
-    before_install:
-    - export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
-    - ghc --version
-    - cabal --version
-    - haddock --version
-    - rm -f ~/.cabal/config && cabal update
-    - cabal install Cabal==1.18.*
-    - cabal install leancheck express speculate
-    script:
-    - make && make test
-    - make haddock HADDOCKFLAGS=
-    - make test-sdist
-    - cabal test
diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -36,11 +36,11 @@
   $(GHCEXTRAFLAGS) \
   $(shell grep -q "Arch Linux" /etc/lsb-release && echo -dynamic)
 #  -Wall -Wno-name-shadowing -Wno-orphans -Wno-unused-matches
-HADDOCKFLAGS = --no-print-missing-docs \
+HADDOCKFLAGS = \
   $(shell grep -q "Arch Linux" /etc/lsb-release && echo --optghc=-dynamic)
 LIST_ALL_HSS = find src test mk eg/*.hs bench/*.hs -name "*.hs"
-LIB_DEPS = base template-haskell leancheck express speculate
-
+LIB_DEPS = base template-haskell $(INSTALL_DEPS)
+INSTALL_DEPS = leancheck express speculate
 all: mk/toplibs
 
 all-all: mk/All.hs
@@ -68,6 +68,14 @@
 
 test-sdist:
 	./test/sdist
+
+test-via-cabal:
+	cabal configure --enable-tests --enable-benchmarks --ghc-options="$(GHCFLAGS) -O0"
+	cabal build
+	cabal test test
+
+test-via-stack:
+	stack test extrapolate:test:test --ghc-options="$(GHCFLAGS) -O0" --system-ghc --no-install-ghc --no-terminal
 
 .PHONY: bench
 bench: $(patsubst %,%.bench,$(EG))
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -154,8 +154,8 @@
 
 [extrapolate-logo]: https://github.com/rudymatela/extrapolate/raw/master/doc/extrapolate.svg?sanitize=true
 
-[build-status]:    https://travis-ci.org/rudymatela/extrapolate.svg?branch=master
-[build-log]:       https://travis-ci.org/rudymatela/extrapolate
+[build-log]:    https://github.com/rudymatela/extrapolate/actions/workflows/build.yml
+[build-status]: https://github.com/rudymatela/extrapolate/actions/workflows/build.yml/badge.svg
 [hackage-version]: https://img.shields.io/hackage/v/extrapolate.svg
 [stackage-lts-badge]:              https://stackage.org/package/extrapolate/badge/lts
 [stackage-nightly-badge]:          https://stackage.org/package/extrapolate/badge/nightly
diff --git a/eg/parser.hs b/eg/parser.hs
--- a/eg/parser.hs
+++ b/eg/parser.hs
@@ -70,17 +70,16 @@
          | Or Exp Exp
   deriving (Show, Read, Typeable, Generic, Eq, Ord)
 
-deriveListable ''Lang
---deriveListable ''Var
-deriveListable ''Mod
-deriveListable ''Func
-deriveListable ''Stmt
+instance Listable Var where
+  tiers = cons1 Var `suchThat` (\(Var s) -> all isAlphaNum s && not (null s))
+
 deriveListable ''Exp
+deriveListable ''Stmt
+deriveListable ''Func
+deriveListable ''Mod
+deriveListable ''Lang
 
 --------------------------------------------------------------------------------
-
-instance Listable Var where
-  tiers = cons1 Var `suchThat` (\(Var s) -> all isAlphaNum s && not (null s))
 
 {-
 instance Listable Lang where
diff --git a/extrapolate.cabal b/extrapolate.cabal
--- a/extrapolate.cabal
+++ b/extrapolate.cabal
@@ -1,5 +1,5 @@
 name:                extrapolate
-version:             0.4.4
+version:             0.4.6
 synopsis:            generalize counter-examples of test properties
 description:
   Extrapolate is a tool able to provide generalized counter-examples of test
@@ -24,7 +24,7 @@
                , TODO.md
                , doc/extrapolate.svg
 extra-source-files: .gitignore
-                  , .travis.yml
+                  , .github/workflows/build.yml
                   , Makefile
                   , bench/versions
                   , bench/diff.hs
@@ -68,7 +68,8 @@
                   , test/model/bench/*.out
                   , test/model/eg/*.out
                   , test/sdist
-tested-with: GHC==8.10
+tested-with: GHC==9.0
+           , GHC==8.10
            , GHC==8.8
            , GHC==8.6
            , GHC==8.4
@@ -84,7 +85,7 @@
 source-repository this
   type:            git
   location:        https://github.com/rudymatela/extrapolate
-  tag:             v0.4.4
+  tag:             v0.4.6
 
 library
   exposed-modules: Test.Extrapolate
diff --git a/mk/haskell.mk b/mk/haskell.mk
--- a/mk/haskell.mk
+++ b/mk/haskell.mk
@@ -21,6 +21,7 @@
 GHC ?= ghc
 GHCCMD = $(GHC) -i$(GHCIMPORTDIRS) $(GHCFLAGS)
 HADDOCK ?= haddock
+CABAL_INSTALL = $(shell cabal --version | grep -q "version [0-2]\." && echo 'cabal install' || echo 'cabal v1-install')
 
 # Hugs Parameters
 HUGSIMPORTDIRS ?= "/usr/lib/hugs/packages/*"
@@ -46,19 +47,13 @@
 
 LIB_DEPS ?= base
 ALL_DEPS ?= $(LIB_DEPS)
+INSTALL_DEPS ?=
 
 PKGNAME = $(shell cat *.cabal | grep "^name:"    | sed -e "s/name: *//")
-HADDOCK_VERSION = $(shell $(HADDOCK) --version | grep version | sed -e 's/.*version //;s/,.*//')
-HADDOCK_MAJOR = $(shell echo $(HADDOCK_VERSION) | sed -e 's/\..*//')
-HADDOCK_MINOR = $(shell echo $(HADDOCK_VERSION) | sed -e 's/[0-9]*\.\([0-9]*\).[0-9]*/\1/')
-HADDOCK_PKG_NAME = $(shell [ $(HADDOCK_MAJOR) -gt 2 ] \
-                        || [ $(HADDOCK_MAJOR) -eq 2 -a $(HADDOCK_MINOR) -ge 20 ] \
-                        && echo "--package-name=$(PKGNAME)")
-HADDOCK_HLNK_SRC = $(shell [ $(HADDOCK_MAJOR) -gt 2 ] \
-                        || [ $(HADDOCK_MAJOR) -eq 2 -a $(HADDOCK_MINOR) -ge 17 ] \
-                        && echo "--hyperlinked-source")
 
+HADDOCK_HAS = haddock --help | grep -q --
 
+
 # Implicit rules
 %.hi %.o: %.hs
 	$(GHCCMD) $< && touch $@
@@ -94,6 +89,9 @@
 depend:
 	find $(ALL_HSS) | ./mk/ghcdeps -i$(GHCIMPORTDIRS) $(GHCFLAGS) > $(DEPMK)
 
+install-dependencies:
+	$(CABAL_INSTALL) $(INSTALL_DEPS)
+
 # haddock rules
 haddock: doc/index.html
 
@@ -110,8 +108,9 @@
 	./mk/haddock-i $(LIB_DEPS) | xargs \
 	$(HADDOCK) --html -odoc $(LIB_HSS) \
 	  --title=$(PKGNAME) \
-	  $(HADDOCK_PKG_NAME) \
-	  $(HADDOCK_HLNK_SRC) \
+	  $(shell $(HADDOCK_HAS) --package-name          && echo "--package-name=$(PKGNAME)" ) \
+	  $(shell $(HADDOCK_HAS) --hyperlinked-source    && echo "--hyperlinked-source"      ) \
+	  $(shell $(HADDOCK_HAS) --no-print-missing-docs && echo --no-print-missing-docs     ) \
 	  $(HADDOCKFLAGS)
 
 clean-cabal:
diff --git a/stack.yaml b/stack.yaml
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,9 +1,9 @@
-resolver: lts-15.6 # or ghc-8.8.3
+resolver: lts-17.9 # or ghc-8.10.4
 
 packages:
 - .
 
 extra-deps:
-- leancheck-0.9.4
-- speculate-0.4.6
-- express-0.1.6
+- leancheck-0.9.10
+- speculate-0.4.8
+- express-0.1.14
