Revamp build: remove Nix, have a single cabal project

.envrc

@@ -1,2 +1,3 @@
-use nix
-source_env_if_exists .envrc.private # allow custom extensions
+PATH_add $HOME/.ghcup/bin
+PATH_add $(pwd)/bin/cabal
+PATH_add $(pwd)/bin/ghc/bin

.github/workflows/haskell.yml

@@ -0,0 +1,75 @@
+# Stripped down version of https://github.com/haskell-actions/setup#model-cabal-workflow-with-caching
+
+name: Haskell build
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  build:
+    name: GHC ${{ matrix.ghc-version }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    defaults:
+      run:
+        working-directory: ./slides
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+        ghc-version: ['9.4.7']
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Extract Haskell snippets from slides
+        working-directory: slides
+        run: |
+          git clone https://github.com/smelc/exdown
+          EXDOWN=exdown/exdown.py ./extract_hs.sh
+
+      - name: Set up GHC ${{ matrix.ghc-version }}
+        uses: haskell-actions/setup@v2
+        id: setup
+        with:
+          ghc-version: ${{ matrix.ghc-version }}
+          # Defaults, added for clarity:
+          cabal-version: '3.6.2.0'
+          cabal-update: true
+
+      - name: Configure the build
+        run: |
+          cabal configure --enable-tests --enable-benchmarks --disable-documentation
+          cabal build all --dry-run
+        # The last step generates dist-newstyle/cache/plan.json for the cache key.
+
+      - name: Restore cached dependencies
+        uses: actions/cache/restore@v3
+        id: cache
+        env:
+          key: ${{ runner.os }}-ghc-${{ steps.setup.outputs.ghc-version }}-cabal-${{ steps.setup.outputs.cabal-version }}
+        with:
+          path: ${{ steps.setup.outputs.cabal-store }}
+          key: ${{ env.key }}-plan-${{ hashFiles('**/plan.json') }}
+          restore-keys: ${{ env.key }}-
+
+      - name: Install dependencies
+        # If we had an exact cache hit, the dependencies will be up to date.
+        if: steps.cache.outputs.cache-hit != 'true'
+        run: cabal build all --only-dependencies
+
+      # Cache dependencies already here, so that we do not have to rebuild them should the subsequent steps fail.
+      - name: Save cached dependencies
+        uses: actions/cache/save@v3
+        # If we had an exact cache hit, trying to save the cache would error because of key clash.
+        if: steps.cache.outputs.cache-hit != 'true'
+        with:
+          path: ${{ steps.setup.outputs.cabal-store }}
+          key: ${{ steps.cache.outputs.cache-primary-key }}
+
+      - name: Build
+        run: cabal build all
+
+      # No tests
+      # - name: Run tests
+      #   run: cabal test all

.gitignore

@@ -1,8 +1,6 @@
 .direnv
 .venv
-ghc
-hls
-tps/dist-newstyle
+bin
+dist-newstyle
 slides/*.java
-slides/app/Course*.hs
-slides/dist-newstyle
+slides/Course*.hs

README.md

@@ -28,16 +28,24 @@ But I've never done it.
 
 ### Development instruction
 
-- GHC and hls are installed in an isolated manner at the top-level of the repo
+- The Haskell compiler (GHC) is installed in an isolated manner, in `bin/ghc` (see below)
 - This requires [ghcup](https://www.haskell.org/ghcup) in `PATH` and that's all
+- When started from this directory, the [vscode Haskell extension](https://github.com/haskell/vscode-haskell)
+  will install the required [language server](https://github.com/haskell/haskell-language-server) on its own,
+  so nothing to do here.
 
 ```
-# Populate GHC, this matches PATH_ADD $(pwd)/ghc/bin in .envrc
-ghcup install ghc 8.10.7 --isolate $(pwd)/ghc
-# Populate hls, this matches PATH_ADD $(pwd)/hls/bin in .envrc
-ghcup install hls --isolate $(pwd)/hls
+mkdir -p bin/ghc
+# Instal cabal, this matches PATH_ADD $(pwd)/bin/ghc/bin in .envrc
+ghcup install cabal --isolate $(pwd)/bin/cabal
+# Populate GHC, this matches PATH_ADD $(pwd)/bin/ghc/bin in .envrc
+# Note that GHC's version number is also in .github/workflows/haskell.yml
+ghcup install ghc 9.4.7 --isolate $(pwd)/bin/ghc
 ```
 
+Because there is a [cabal.project](./cabal.project) file that pins the set of packages to a specific
+timestamp, this project is highly reproducible.
+
 ---
 
 This course is funded by my employer: [Tweag](https://www.tweag.io/)

cabal.project

@@ -0,0 +1,2 @@
+packages: .
+index-state: 2023-08-22T10:00:00Z