adding workflows and README

.github/workflows/build.yaml

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+# Build tagged versions of the reference implementation compiler
+name: Build the compiler
+
+on:
+  workflow_dispatch:
+    inputs:
+      chapter:
+        required: true
+        type: string
+      os:
+        required: true
+        default: ubuntu-latest
+
+  workflow_call:
+    inputs:
+      chapter:
+        required: true
+        type: number
+      os:
+        type: string
+        required: true
+        default: ubuntu-latest
+      branch:
+        type: string
+        required: false
+        default: main
+
+env:
+  EXE_DIR: _build/default/bin/
+  EXE_PATH: _build/default/bin/main.exe
+
+jobs:
+
+  build:
+    runs-on: ${{ inputs.os }}
+    env:
+      CHAPTER: ${{ inputs.chapter }}
+
+    steps:
+
+      # first check out at specified branch so we can find commit hash for this chapter
+      - uses: actions/checkout@v4
+        with:
+          repository: nlsandler/nqcc2
+          ref: ${{ inputs.branch }}
+          fetch-depth: 0 # need this to get commit history
+
+      - name: Get commit hash
+        run: |
+          git log --grep "chapter $CHAPTER:" -i --format='%H'
+          commit=$(git log --grep "chapter $CHAPTER:" -i --format='%H')
+          echo "commit=$commit" >> $GITHUB_ENV
+
+      - name: Check out NQCC at chapter ${{ inputs.chapter }}
+        uses: actions/checkout@v4
+        with:
+          repository: nlsandler/nqcc2
+          ref: ${{ env.commit }}
+
+      - name: Construct cache key
+        id: make-key
+        env:
+          runner_os: ${{ runner.os }}
+        run: |
+          commit=$(git rev-parse --short "$commit")
+          echo "cache-key=${runner_os}-${commit}-nqcc" >> $GITHUB_OUTPUT
+
+      - name: Cache build result
+        id: cache-nqcc
+        uses: actions/cache@v4
+        with:
+          path: ${{ env.EXE_PATH }}
+          key: ${{ steps.make-key.outputs.cache-key }}
+
+      # skip building if we get a cache hit
+      - name: Set up OCaml
+        if: steps.cache-nqcc.outputs.cache-hit != 'true'
+        uses: ocaml/setup-ocaml@v2
+        with:
+          ocaml-compiler: 4.14.x
+          # necessary to avoid random errors, see https://github.com/ocaml/setup-ocaml/issues/400
+          dune-cache: false
+
+      - name: Build it
+        if: steps.cache-nqcc.outputs.cache-hit != 'true'
+        run: |
+          opam install . --deps-only
+          opam exec -- dune build
+
+      - name: Upload binary
+        uses: actions/upload-artifact@v4
+        with:
+          name: nqcc-${{inputs.os}}-${{ inputs.chapter }}
+          path: ${{ env.EXE_PATH }}

.github/workflows/build_and_test.yaml

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+name: Build and test the compiler
+
+on:
+  workflow_call:
+    inputs:
+      os:
+        required: true
+        type: string
+      chapter:
+        required: true
+        type: number
+
+jobs:
+  build:
+    uses: nlsandler/nqcc2/.github/workflows/build.yaml@main
+    with:
+      chapter: ${{ inputs.chapter }}
+      os: ${{ inputs.os }}
+
+  test:
+    runs-on: ${{ inputs.os }}
+    needs: [build]
+    env:
+      CHAPTER: ${{ inputs.chapter }}
+    steps:
+
+      - name: Check out tests
+        uses: actions/checkout@v4
+        with:
+          repository: nlsandler/writing-a-c-compiler-tests
+          ref: complete-test-suite # TODO use main once this is merged
+
+      - name: Download the compiler
+        uses: actions/download-artifact@v4
+        with:
+          name: nqcc-${{inputs.os}}-${{ inputs.chapter }}
+          path: nqcc
+
+      # make NQCC executable
+      - run: chmod u+x nqcc/main.exe
+
+      # TODO handle intermediate stages w/in chapters 19, 20
+      - name: Test the lexer
+        if: inputs.chapter < 19
+        run: |
+          ./test_compiler nqcc/main.exe --chapter "$CHAPTER" --stage lex
+
+      - name: Test the parser
+        if: inputs.chapter < 19
+        run: |
+          ./test_compiler nqcc/main.exe --chapter "$CHAPTER" --stage parse
+
+      - name: Test validation
+        if: inputs.chapter < 19 && inputs.chapter > 4
+        run: |
+          ./test_compiler nqcc/main.exe --chapter "$CHAPTER" --stage validate
+
+      - name: Test TACKY generation
+        if: inputs.chapter < 19 && inputs.chapter > 1
+        run: |
+          ./test_compiler nqcc/main.exe --chapter "$CHAPTER" --stage tacky
+
+      - name: Test assembly generation
+        if: inputs.chapter < 19 && inputs.chapter > 1
+        run: |
+          ./test_compiler nqcc/main.exe --chapter "$CHAPTER" --stage codegen
+
+      - name: Test the whole compiler
+        run: ./test_compiler nqcc/main.exe --chapter "$CHAPTER"
+

.github/workflows/test_each_chapter.yaml

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+name: Build and test each chapter
+
+on:
+  workflow_dispatch:
+
+jobs:
+
+
+  build-and-test:
+    strategy:
+      fail-fast: true
+      matrix:
+        os: [macos-latest, ubuntu-latest]
+        chapter: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
+    uses: nlsandler/nqcc2/.github/workflows/build_and_test.yaml@main
+    with:
+      chapter: ${{ matrix.chapter }}
+      os: ${{ matrix.os }}

README.md

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+# NQCC2, the Not-Quite-C Compiler
+
+**CAUTION: FREQUENT FORCE PUSHES**
+
+This is the reference implementation for the upcoming book [Writing a C Compiler](https://nostarch.com/writing-c-compiler), a hands-on guide to writing your own compiler for a big chunk of C.
+
+Each commit corresponds to one chapter in the book, to illustrate what needs to change at each step. Because commits are structured this way, this repository sees frequent rebases and force pushes - fork with caution!
+
+This implementation is still a work in progress - the functionality is complete, but needs more work on the readability front.
+
+# Building the Compiler
+
+This compiler is written in OCaml. Building it requires opam, the OCaml package manager (installation instructions [here](https://opam.ocaml.org/doc/Install.html)).
+
+Then do:
+
+```
+git clone https://github.com/nlsandler/nqcc2.git
+cd nqcc2
+opam install . --deps-only
+dune build
+```
+
+This puts the executable at `_build/default/bin/main.exe`.
+
+# Usage Example
+
+Assume we have this source file at ~/hello_world.c:
+```c
+int puts(char *c);
+
+int main(void) {
+    puts("Hello, world!");
+}
+```
+
+To compile and run it:
+```
+$ _build/default/bin/main.exe ~/hello_world.c
+$ ~/hello_world
+Hello, World!
+```
+
+
+
+
+
+