[fix] update to ghc 94

- fix the compile errors
- fix the test failures
- add github workflows to verify it keeps working
- add nix env
- prepare flake update such that we can update easily in the future
- reformat with stylish-haskell as good as possible

.envrc

@@ -0,0 +1 @@
+use flake -Lv 

.github/workflows/test-flake.yml

@@ -0,0 +1,16 @@
+name: "Check Flake"
+on:
+  workflow_dispatch:
+  pull_request:
+  push:
+jobs:
+  install-nix:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: cachix/install-nix-action@v22
+      with:
+        github_access_token: ${{ secrets.GITHUB_TOKEN }}
+    - run: nix flake check -Lv --allow-import-from-derivation --fallback
+    - run: nix build -Lv --fallback
+    - run: nix build .#ghc92-transitive-anns -Lv --fallback

.github/workflows/update-flake-lock.yml

@@ -0,0 +1,21 @@
+name: update-flake-lock
+on:
+  workflow_dispatch: # allows manual triggering
+  schedule:
+    - cron: '0 0 * * 0' # runs weekly on Sunday at 00:00
+
+jobs:
+  lockfile:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+      - name: Update flake.lock
+        uses: DeterminateSystems/update-flake-lock@main
+        with:
+          pr-title: "Update flake.lock" # Title of PR to be created
+          pr-labels: |                  # Labels to be set on the PR
+            dependencies
+            automated

.gitignore

@@ -1,2 +1,6 @@
 .stack-work/
-*~
+*~
+.direnv
+dist*
+result*
+.pre-commit-config.yaml