setup workflow to run CI

.github/workflows/ci.yml

@@ -0,0 +1,31 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+
+      - name: install elan
+        run: |
+          curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh -s -- -y --default-toolchain $(cat lean-toolchain)
+          echo "$HOME/.elan/bin" >> $GITHUB_PATH
+
+      - name: Cache dependencies
+        uses: actions/cache@v3
+        with:
+          path: .lake
+          key: deps-${{ runner.os }}-${{ hashFiles('lean-toolchain') }}-${{ hashFiles('lake-manifest.json') }}
+          restore-keys: |
+            deps-${{ runner.os }}-${{ hashFiles('lean-toolchain') }}
+
+      - name: lake build
+        run: lake build --quiet

lakefile.lean

@@ -4,6 +4,7 @@ open Lake DSL
 package «lean4-metaprogramming-book» where
   srcDir := "lean"
 
+@[default_target]
 lean_lib «lean4-metaprogramming-book» where
   roots := #[`cover, `extra, `main, `solutions]
   globs := #[Glob.one `cover, Glob.submodules `extra, Glob.submodules `main, Glob.submodules `solutions]