diff --git a/.github/workflows/cachix.yaml b/.github/workflows/cachix.yaml
index e67eb4f..1ecf070 100644
--- a/.github/workflows/cachix.yaml
+++ b/.github/workflows/cachix.yaml
@@ -4,9 +4,37 @@ on:
   push:
     branches: [master]
 jobs:
-  Nix-CI:
-    name: 
+
+  # Nix builds
+  Nix-Build:
     runs-on: ubuntu-latest
+    # Build for 3 latest Stackage package sets
+    strategy:
+      matrix:
+        package-set: [lts-20, lts-19, lts-18]
+    steps:
+    - uses: actions/checkout@v3
+    - uses: cachix/install-nix-action@v17
+      with:
+        extra_nix_config: |
+          trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+          substituters = https://hydra.iohk.io https://cache.nixos.org/
+    - uses: cachix/cachix-action@v10
+      with:
+        name: brechtserckx-openscad
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+
+    # Nix build
+    - run: make nix-build PACKAGE_SET=${{matrix.package-set}}
+
+    # Cabal build in nix-shell
+    - run: nix-shell --argstr packageSet ${{matrix.package-set}} --run "make build"
+
+  # Additional package checking using nix
+  Nix-Check:
+    runs-on: ubuntu-latest
+    # Only run after build completed, to re-use caching
+    needs: Nix-Build
     steps:
     - uses: actions/checkout@v3
     - uses: cachix/install-nix-action@v17
@@ -18,6 +46,4 @@ jobs:
       with:
         name: brechtserckx-openscad
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-    - run: make nix-build
-    - run: nix-shell --run "echo 'Shell ok'"
     - run: nix-shell --run "make check"
diff --git a/Makefile b/Makefile
index 399c72a..c3f4fe0 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,13 @@
 SHELL := /usr/bin/env bash
 
+ifdef PACKAGE_SET
+	NIX_ARGS += --argstr packageSet $(PACKAGE_SET)
+endif
+
+.PHONY: info
+info:
+	echo "NIX_ARGS: '$(NIX_ARGS)'"
+
 .PHONY: clean
 clean:
 	rm -rf dist-newstyle result result-* bench/out/*
@@ -13,12 +21,12 @@ test:
 	cabal test OpenSCAD
 
 .PHONY: bench
-test:
+bench:
 	cabal bench
 
 .PHONY: nix-build
 nix-build:
-	nix-build --no-out-link default.nix -A OpenSCAD.components
+	nix-build $(NIX_ARGS) --no-out-link default.nix -A OpenSCAD.components
 
 .PHONY: format
 format:
@@ -40,6 +48,14 @@ hlint:
 ci-cd: 
 	act $(ACT_ARGS)
 
-.PHONY: make check
+.PHONY: check
 check: format-check hlint
 	cabal check
+
+.PHONY: haddock
+haddock: 
+	cabal haddock
+
+.PHONY: doctest
+doctest: 
+	doctest
diff --git a/OpenSCAD.cabal b/OpenSCAD.cabal
index 38089dc..445e758 100644
--- a/OpenSCAD.cabal
+++ b/OpenSCAD.cabal
@@ -19,7 +19,7 @@ description:
   functions for rendering an ADT into an OpenSCAD program.
 
 category:        Graphics
-tested-with:     GHC ==8.6.5 || ==8.8.4 || ==8.10.7 || ==9.0.2 || ==9.2.2
+tested-with:     GHC ==8.10.7 || ==9.0.2 || ==9.2.2
 extra-doc-files: README.md
 
 library
diff --git a/default.nix b/default.nix
index 7dedfff..484d39e 100644
--- a/default.nix
+++ b/default.nix
@@ -1,7 +1,14 @@
+{ packageSet ? null }:
 let
   pkgs = import ./nix/pkgs.nix;
   cleanSource = pkgs.haskell-nix.haskellLib.cleanGit;
-in pkgs.haskell-nix.project {
+in pkgs.haskell-nix.stackProject {
+  stackYaml = if isNull packageSet || packageSet == "lts-20" then
+    "stack.yaml"
+  else if builtins.elem packageSet [ "lts-19" "lts-18" ] then
+    "stack-${toString packageSet}.yaml"
+  else
+    abort "packageSet must be one of <null>, lts-19 or lts-18";
   src = cleanSource {
     name = "OpenSCAD";
     src = ./.;
diff --git a/nix/sources.json b/nix/sources.json
index 584bd82..7783bb8 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -5,10 +5,10 @@
         "homepage": "https://input-output-hk.github.io/haskell.nix",
         "owner": "input-output-hk",
         "repo": "haskell.nix",
-        "rev": "9bc8625f18ed1aa633f5f3a52ee03d1718eaeebe",
-        "sha256": "0mm4z0wc7vic1185id912lfmrm2vy8ky25qa2ivf8fphi4ls5qb8",
+        "rev": "a6825537df7c0834a4410f652b6659e07ec5bde3",
+        "sha256": "1nqm48clz0739l11gzyfacs3mfs4rygiyhdcac9kynjk0mqb0xyn",
         "type": "tarball",
-        "url": "https://github.com/input-output-hk/haskell.nix/archive/9bc8625f18ed1aa633f5f3a52ee03d1718eaeebe.tar.gz",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/a6825537df7c0834a4410f652b6659e07ec5bde3.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "niv": {
diff --git a/nix/sources.nix b/nix/sources.nix
index 1938409..9a01c8a 100644
--- a/nix/sources.nix
+++ b/nix/sources.nix
@@ -31,8 +31,28 @@ let
           if spec ? branch then "refs/heads/${spec.branch}" else
             if spec ? tag then "refs/tags/${spec.tag}" else
               abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+      submodules = if spec ? submodules then spec.submodules else false;
+      submoduleArg =
+        let
+          nixSupportsSubmodules = builtins.compareVersions builtins.nixVersion "2.4" >= 0;
+          emptyArgWithWarning =
+            if submodules == true
+            then
+              builtins.trace
+                (
+                  "The niv input \"${name}\" uses submodules "
+                  + "but your nix's (${builtins.nixVersion}) builtins.fetchGit "
+                  + "does not support them"
+                )
+                {}
+            else {};
+        in
+          if nixSupportsSubmodules
+          then { inherit submodules; }
+          else emptyArgWithWarning;
     in
-      builtins.fetchGit { url = spec.repo; inherit (spec) rev; inherit ref; };
+      builtins.fetchGit
+        ({ url = spec.repo; inherit (spec) rev; inherit ref; } // submoduleArg);
 
   fetch_local = spec: spec.path;
 
diff --git a/shell.nix b/shell.nix
index bbd9261..f8c8d12 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,5 +1,6 @@
+args@{ packageSet ? null }:
 let
-  project = import ./default.nix;
+  project = import ./default.nix args;
   pkgs = import ./nix/pkgs.nix;
   sources = import ./nix/sources.nix { };
 in project.shellFor {
@@ -7,7 +8,7 @@ in project.shellFor {
 
   withHoogle = true;
 
-  tools = {
+  tools = if isNull packageSet || packageSet == "lts-20" then {
     cabal = "3.6.2.0";
     hlint = "3.5";
     ghcid = "0.8.7";
@@ -15,7 +16,16 @@ in project.shellFor {
     haskell-ci = "0.14.3";
     haskell-language-server = "1.9.1.0";
     cabal-fmt = "0.1.6";
-  };
+  } else if packageSet == "lts-19" then {
+    cabal = "3.4.1.0";
+    ghcid = "0.8.7";
+    haskell-language-server = "1.9.0.0";
+  } else if packageSet == "lts-18" then {
+    cabal = "3.2.0.0";
+    ghcid = "0.8.7";
+    haskell-language-server = "1.8.0.0";
+  } else
+    abort "packageSet must be one of <null>, lts-19 or lts-18";
 
   buildInputs = with pkgs; [
     nixfmt
@@ -23,7 +33,15 @@ in project.shellFor {
     cmake
     bash
     openscad
+    # not available from haskell.nix?
+    pkgs.haskellPackages.doctest
   ];
 
   exactDeps = true;
+
+  shellHook = if isNull packageSet then
+    ""
+  else ''
+    export PACKAGE_SET=${packageSet}
+  '';
 }
diff --git a/stack-lts-18.yaml b/stack-lts-18.yaml
new file mode 100644
index 0000000..a7a9e29
--- /dev/null
+++ b/stack-lts-18.yaml
@@ -0,0 +1,5 @@
+flags: {}
+packages:
+- '.'
+extra-deps: []
+resolver: lts-18.28
diff --git a/stack-lts-19.yaml b/stack-lts-19.yaml
new file mode 100644
index 0000000..786fa82
--- /dev/null
+++ b/stack-lts-19.yaml
@@ -0,0 +1,5 @@
+flags: {}
+packages:
+- '.'
+extra-deps: []
+resolver: lts-19.33