Lint workflow

.github/workflows/lint.yml

@@ -0,0 +1,30 @@
+name: Lint
+
+# Trigger the workflow on push or pull request, but only for the master branch
+on:
+  pull_request:
+  push:
+    branches: [master]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      if: github.event.action == 'opened' || github.event.action == 'synchronize' || github.event.ref == 'refs/heads/master'
+
+    - name: Check code is formatted using Ormolu
+      run: |
+        curl -L https://github.com/tweag/ormolu/releases/download/0.7.2.0/ormolu-Linux.zip -o ormolu.zip
+        unzip ormolu.zip
+
+        git ls-files | grep -v 'example/' | grep \.hs | xargs ./ormolu --mode=inplace
+
+        if [[ $(git diff --stat) != '' ]]; then
+          echo "Lint stage failed, running ormolu has returned changes"
+          echo "$(git diff)"
+          exit 1
+        else
+          echo "Lint stage succeeded"
+          exit 0
+        fi

README.md

@@ -62,6 +62,16 @@ Y ou can install the executable with using:
 $ cabal install .
 ```
 
+## Formatting
+
+To pass the lint workflow run
+
+```
+$ git ls-files | grep -v 'example/' | grep \.hs | xargs ./ormolu --mode=inplace
+```
+
+to format the Haskell files accordingly using Ormolu.
+
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