Add github actions workflow

Author: dmjio

.github/workflows/main.yml

@@ -0,0 +1,29 @@
+name: GHC-WPC CI
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    if: github.ref != 'refs/heads/master'
+    steps:
+     - uses: DeterminateSystems/nix-installer-action@main
+     - name: Cancel Previous Runs
+       uses: styfle/cancel-workflow-action@0.9.1
+       with:
+         access_token: ${{ github.token }}
+
+     - name: Nix channel update
+       run: nix-channel --update
+
+     - name: Cabal install
+       run: nix-env -iA cabal-install -f '<nixpkgs>'
+
+     - name: Build external-stg-interpreter
+       run: nix-shell -p ghc -p bzip2.dev -p zlib.dev --run 'cabal build external-stg-interpreter'
+
+     - name: Test external-stg-interpreter
+       run: nix-shell -p 'haskellPackages.ghcWithPackages (p: with p; [ hspec-discover ])' --run 'cabal test external-stg-interpreter'