Add GitHub CI (#81)

.github/workflows/haskell.yml

@@ -0,0 +1,34 @@
+name: Haskell CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: haskell/actions/setup@v1.2
+    - name: Cache
+      uses: actions/cache@v1
+      env:
+        cache-name: cache-cabal
+      with:
+        path: ~/.cabal
+        key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/*.cabal') }}-${{ hashFiles('**/cabal.project') }}
+        restore-keys: |
+          ${{ runner.os }}-build-${{ env.cache-name }}-
+          ${{ runner.os }}-build-
+          ${{ runner.os }}-
+
+    - name: Install dependencies
+      run: |
+        cabal update
+        cabal build --only-dependencies --enable-tests --enable-benchmarks
+    - name: Build
+      run: cabal build --enable-tests --enable-benchmarks all