diff --git a/.clang-format b/.clang-format
new file mode 100644
index 0000000..053f31e
--- /dev/null
+++ b/.clang-format
@@ -0,0 +1,3 @@
+UseTab: Always
+IndentWidth: 4
+TabWidth: 4
diff --git a/.editorconfig b/.editorconfig
index ca93d68..88ce455 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -1,7 +1,15 @@
-root = true
-
-[*]
-end_of_line = lf
-insert_final_newline = true
-indent_style = tab
-indent_size = 4
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+indent_style = tab
+indent_size = 4
+
+[*.{sh,cmd}]
+indent_size = 4
+indent_style = space
+
+[*.{yml,yaml}]
+indent_size = 2
+indent_style = space
diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
new file mode 100644
index 0000000..b8cbaa2
--- /dev/null
+++ b/.github/workflows/main.yaml
@@ -0,0 +1,87 @@
+name: main
+
+on:
+  pull_request:
+
+env:
+  # libcxx version to match whats already installed
+  # https://github.com/actions/runner-images/blob/main/images/ubuntu/Ubuntu2404-Readme.md
+  LLVM_VERSION: '18.1.3'
+
+jobs:
+  typos-check:
+    name: Typos Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: crate-ci/typos@cfe759ac8dd421e203cc293a373396fbc6fe0d4b # v1.22.7
+
+  build-script-windows:
+    name: 'build.cmd'
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - run: .\build.cmd
+      - uses: actions/upload-artifact@v4
+        with:
+          name: cpp2b.exe
+          path: dist/debug/cpp2b.exe
+          if-no-files-found: error
+          retention-days: 0
+
+  build-self-windows:
+    name: 'build self (windows)'
+    needs: build-script-windows
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: 'cpp2b.exe'
+      - run: .\cpp2b.exe build
+      - run: Copy-Item .\.cache\cpp2\bin\cpp2b.exe -Destination .\cpp2b-self.exe
+      - run: .\cpp2b-self.exe build
+
+  build-script-linux:
+    name: 'build.sh'
+    runs-on: ubuntu-24.04
+    steps:
+      - run: sudo apt-get install libclang-dev ninja-build -y
+      - uses: actions/cache@v4
+        id: libcxx_with_modules
+        with:
+          path: /tmp/llvm-project/build
+          key: 'libcxx-${{ env.LLVM_VERSION }}'
+      - name: compiling libcxx ${{ env.LLVM_VERSION }} with modules
+        if: steps.libcxx_with_modules.outputs.cache-hit != 'true'
+        run: |
+          git clone --depth 1 --branch llvmorg-${{ env.LLVM_VERSION }} https://github.com/llvm/llvm-project.git /tmp/llvm-project
+          cd /tmp/llvm-project
+          mkdir build
+          CC=clang-18 CXX=clang++-18 cmake -G Ninja -S runtimes -B build -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind"
+          ninja -C build
+      - uses: actions/checkout@v4
+      - run: CPP2B_LIBCXX_BUILD_ROOT=/tmp/llvm-project/build CC=clang-18 ./build.sh
+      - uses: actions/upload-artifact@v4
+        with:
+          name: cpp2b
+          path: dist/debug/cpp2b
+          if-no-files-found: error
+          retention-days: 0
+
+  build-self-linux:
+    name: 'build self (linux)'
+    needs: build-script-linux
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/cache/restore@v4
+        with:
+          path: /tmp/llvm-project/build
+          key: 'libcxx-${{ env.LLVM_VERSION }}'
+      - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: cpp2b
+      - run: chmod +x cpp2b
+      - run: CPP2B_LIBCXX_BUILD_ROOT=/tmp/llvm-project/build ./cpp2b build
+      - run: CPP2B_LIBCXX_BUILD_ROOT=/tmp/llvm-project/build ./.cache/cpp2/bin/cpp2b build
diff --git a/build.cmd b/build.cmd
index ccad0f5..ef289fe 100644
--- a/build.cmd
+++ b/build.cmd
@@ -18,40 +18,40 @@ if not exist dist\debug ( mkdir dist\debug )
 set vswhere="%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe"
 
 for /f "usebackq tokens=*" %%i in (`%vswhere% -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do (
-	set vs_install_dir=%%i
+    set vs_install_dir=%%i
 )
 
 if exist "%vs_install_dir%\VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt" (
-	set /p vs_tools_version=<"%vs_install_dir%\VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt"
+    set /p vs_tools_version=<"%vs_install_dir%\VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt"
 )
 
 if "%vs_tools_version%"=="" (
-	echo ERROR: cannot find VC tools installed on your system
-	exit 1
+    echo ERROR: cannot find VC tools installed on your system
+    exit 1
 )
 
 set vs_tools_dir=%vs_install_dir%\VC\Tools\MSVC\%vs_tools_version%
 
 if exist .cache\repos\cppfront\ (
-	@rem TODO - report which cppfront version is being used
+    @rem TODO - report which cppfront version is being used
 ) else (
-	git clone https://github.com/hsutter/cppfront.git .cache/repos/cppfront --quiet
+    git clone https://github.com/hsutter/cppfront.git .cache/repos/cppfront --quiet
 )
 
 call "%vs_install_dir%\Common7\Tools\vsdevcmd.bat" /no_logo
 
 if not exist "%modules_dir%\std.ifc" (
-	echo Compiling std module...
-	pushd %modules_dir%
-	cl /D"_CRT_SECURE_NO_WARNINGS=1" /std:c++latest /EHsc /nologo /W4 /MDd /c "%vs_tools_dir%\modules\std.ixx"
-	popd
+    echo Compiling std module...
+    pushd %modules_dir%
+    cl /D"_CRT_SECURE_NO_WARNINGS=1" /std:c++latest /EHsc /nologo /W4 /MDd /c "%vs_tools_dir%\modules\std.ixx"
+    popd
 )
 
 if not exist "%modules_dir%\std.compat.ifc" (
-	echo Compiling std.compat module...
-	pushd %modules_dir%
-	cl /std:c++latest /EHsc /nologo /W4 /MDd /c "%vs_tools_dir%\modules\std.compat.ixx"
-	popd
+    echo Compiling std.compat module...
+    pushd %modules_dir%
+    cl /std:c++latest /EHsc /nologo /W4 /MDd /c "%vs_tools_dir%\modules\std.compat.ixx"
+    popd
 )
 
 if not exist "%root_dir%.cache\cpp2\source\_build" ( mkdir "%root_dir%.cache\cpp2\source\_build" )
@@ -72,37 +72,37 @@ endlocal
 
 pushd %modules_dir%
 cl /nologo ^
-  /std:c++latest /W4 /MDd /EHsc ^
-  /reference "%modules_dir%\std.ifc" ^
-  /reference "%modules_dir%\std.compat.ifc" ^
-  /c "%root_dir%.cache\cpp2\source\_build\cpp2b.ixx" > NUL
+    /std:c++latest /W4 /MDd /EHsc ^
+    /reference "%modules_dir%\std.ifc" ^
+    /reference "%modules_dir%\std.compat.ifc" ^
+    /c "%root_dir%.cache\cpp2\source\_build\cpp2b.ixx" > NUL
 popd
 
 if %ERRORLEVEL% neq 0 (
-	echo ERROR: failed to compile cpp2b module
-	exit %ERRORLEVEL%
+    echo ERROR: failed to compile cpp2b module
+    exit %ERRORLEVEL%
 )
 
 echo INFO: compiling dylib module...
 pushd %modules_dir%
 cl /nologo ^
-  /std:c++latest /W4 /MDd /EHsc ^
-  /reference "%modules_dir%\std.ifc" ^
-  /reference "%modules_dir%\std.compat.ifc" ^
-  /c /interface /TP "%root_dir%src\dylib.cppm" > NUL
+    /std:c++latest /W4 /MDd /EHsc ^
+    /reference "%modules_dir%\std.ifc" ^
+    /reference "%modules_dir%\std.compat.ifc" ^
+    /c /interface /TP "%root_dir%src\dylib.cppm" > NUL
 popd
 
 if %ERRORLEVEL% neq 0 (
-	echo ERROR: failed to compile dylib module
-	exit %ERRORLEVEL%
+    echo ERROR: failed to compile dylib module
+    exit %ERRORLEVEL%
 )
 
 if not exist %cppfront% (
-	pushd .cache\repos\cppfront\source
-	echo INFO: compiling cppfront...
-	cl /nologo /std:c++latest /EHsc cppfront.cpp
-	xcopy cppfront.exe %tools_dir% /Y /Q
-	popd
+    pushd .cache\repos\cppfront\source
+    echo INFO: compiling cppfront...
+    cl /nologo /std:c++latest /EHsc cppfront.cpp
+    xcopy cppfront.exe %tools_dir% /Y /Q
+    popd
 )
 
 if not exist "%root_dir%.cache/cpp2/source/src" ( mkdir "%root_dir%.cache/cpp2/source/src" )
@@ -113,16 +113,16 @@ if %ERRORLEVEL% neq 0 exit %ERRORLEVEL%
 
 
 cl /nologo "%root_dir%.cache/cpp2/source/src/main.cpp" ^
-  /diagnostics:column /permissive- ^
-  /reference "%modules_dir%\std.ifc" "%modules_dir%\std.obj" ^
-  /reference "%modules_dir%\std.compat.ifc" "%modules_dir%\std.compat.obj" ^
-  /reference "%modules_dir%\dylib.ifc" "%modules_dir%\dylib.obj" ^
-  /reference "%modules_dir%\cpp2b.ifc" "%modules_dir%\cpp2b.obj" ^
-  /std:c++latest /W4 /MDd /EHsc ^
-  /DEBUG:FULL /Zi /FC ^
-  -I"%cppfront_include_dir%" ^
-  /Fe"%cpp2b_dist%" ^
-  /Fd"%cpp2b_dist%.pdb"
+    /diagnostics:column /permissive- ^
+    /reference "%modules_dir%\std.ifc" "%modules_dir%\std.obj" ^
+    /reference "%modules_dir%\std.compat.ifc" "%modules_dir%\std.compat.obj" ^
+    /reference "%modules_dir%\dylib.ifc" "%modules_dir%\dylib.obj" ^
+    /reference "%modules_dir%\cpp2b.ifc" "%modules_dir%\cpp2b.obj" ^
+    /std:c++latest /W4 /MDd /EHsc ^
+    /DEBUG:FULL /Zi /FC ^
+    -I"%cppfront_include_dir%" ^
+    /Fe"%cpp2b_dist%" ^
+    /Fd"%cpp2b_dist%.pdb"
 
 if %ERRORLEVEL% neq 0 exit %ERRORLEVEL%
 
diff --git a/build.sh b/build.sh
index 97f42e6..34d557d 100755
--- a/build.sh
+++ b/build.sh
@@ -22,24 +22,24 @@ mkdir -p $ROOT_DIR/.cache/cpp2/source/_build
 CPP2B_COMPILER=${CC:=clang}
 
 function log_info() {
-  echo "INFO: $1"
+    echo "INFO: $1"
 }
 
 function log_error() {
-  echo "ERROR: $1"
+    echo "ERROR: $1"
 }
 
 function fatal() {
-  echo "FATAL: $1"
-  exit 1
+    echo "FATAL: $1"
+    exit 1
 }
 
 if ! [ -x "$(command -v $CPP2B_COMPILER)" ]; then
-  fatal "cannot find $CPP2B_COMPILER in your PATH"
+    fatal "cannot find $CPP2B_COMPILER in your PATH"
 fi
 
 if ! [[ $CPP2B_COMPILER == *"clang"* ]]; then
-	fatal "only clang is supported: detected $CPP2B_COMPILER"
+    fatal "only clang is supported: detected $CPP2B_COMPILER"
 fi
 
 COMPILER_VERSION=$($CPP2B_COMPILER --version | grep -oE '[0-9]+\.[0-9]+\.[0-9]+' | head -n 1)
@@ -49,37 +49,37 @@ if [ "$COMPILER_MAJOR_VERSION" -lt 18 ]; then
 fi
 
 if [[ -z "${CPP2B_LIBCXX_BUILD_ROOT}" ]]; then
-  log_error "libcxx with module support must be built from source"
-  log_error "follow these instructions https://github.com/llvm/llvm-project/blob/main/libcxx/docs/Modules.rst"
-  fatal "missing CPP2B_LIBCXX_BUILD_ROOT environment variable"
+    log_error "libcxx with module support must be built from source"
+    log_error "follow these instructions https://github.com/llvm/llvm-project/blob/main/libcxx/docs/Modules.rst"
+    fatal "missing CPP2B_LIBCXX_BUILD_ROOT environment variable"
 fi
 
 log_info "using libcxx build root $CPP2B_LIBCXX_BUILD_ROOT"
 
 if ! [ -d $CPP2B_LIBCXX_BUILD_ROOT ]; then
-  log_fatal "directory $CPP2B_LIBCXX_BUILD_ROOT does not exixt"
+    log_fatal "directory $CPP2B_LIBCXX_BUILD_ROOT does not exist"
 fi
 
 function ensure_gh_repo() {
-  local repo=$1
-  local repo_path=$ROOT_DIR/.cache/repos/$repo
-  if ! [ -d $repo_path ]; then
-    mkdir -p $repo_path
-    git clone --quiet --depth=1 --filter=blob:none --sparse https://github.com/$repo $repo_path
-  fi
+    local repo=$1
+    local repo_path=$ROOT_DIR/.cache/repos/$repo
+    if ! [ -d $repo_path ]; then
+        mkdir -p $repo_path
+        git clone --quiet --depth=1 --filter=blob:none --sparse https://github.com/$repo $repo_path
+    fi
 }
 
 function ensure_gh_repo_subdir() {
-  local repo=$1
-  local repo_path=$ROOT_DIR/.cache/repos/$repo
-  local repo_subdir=$2
-  local repo_subdir_path=$repo_path/$repo_subdir
-  if ! [ -d $repo_subdir_path ]; then
-    cd $repo_path
-    log_info "checking out repo $repo/$reposubdir"
-    git sparse-checkout add $repo_subdir
-    cd $ROOT_DIR
-  fi
+    local repo=$1
+    local repo_path=$ROOT_DIR/.cache/repos/$repo
+    local repo_subdir=$2
+    local repo_subdir_path=$repo_path/$repo_subdir
+    if ! [ -d $repo_subdir_path ]; then
+        cd $repo_path
+        log_info "checking out repo $repo/$reposubdir"
+        git sparse-checkout add $repo_subdir
+        cd $ROOT_DIR
+    fi
 }
 
 ensure_gh_repo "hsutter/cppfront"
@@ -93,26 +93,26 @@ LIBCXX_INCLUDE_DIR=$CPP2B_LIBCXX_BUILD_ROOT/include
 LIBCXX_LIB_DIR=$CPP2B_LIBCXX_BUILD_ROOT/lib
 
 if ! [ -x $CPPFRONT ]; then
-  log_info "compiling cppfront..."
-  cd $ROOT_DIR/.cache/repos/hsutter/cppfront/source
-  $CPP2B_COMPILER -lstdc++ -lc -lm -fuse-ld=lld -std=c++23 cppfront.cpp -o $CPPFRONT
-  cd $ROOT_DIR
+    log_info "compiling cppfront..."
+    cd $ROOT_DIR/.cache/repos/hsutter/cppfront/source
+    $CPP2B_COMPILER -lstdc++ -lc -lm -fuse-ld=lld -std=c++23 cppfront.cpp -o $CPPFRONT
+    cd $ROOT_DIR
 fi
 
 if ! [ -f $MODULES_DIR/std.pcm ]; then
-  cd $LIBCXX_MODULES_DIR/c++/v1
-  log_info "compiling std module..."
+    cd $LIBCXX_MODULES_DIR/c++/v1
+    log_info "compiling std module..."
+
+    $CPP2B_COMPILER                        \
+        -stdlib=libc++                       \
+        -std=c++23                           \
+        -fexperimental-library               \
+        -isystem $LIBCXX_INCLUDE_DIR/c++/v1  \
+        -Wno-reserved-module-identifier      \
+        std.cppm                             \
+        --precompile -o $MODULES_DIR/std.pcm
 
-  $CPP2B_COMPILER                        \
-    -stdlib=libc++                       \
-    -std=c++23                           \
-    -fexperimental-library               \
-    -isystem $LIBCXX_INCLUDE_DIR/c++/v1  \
-    -Wno-reserved-module-identifier      \
-    std.cppm                             \
-    --precompile -o $MODULES_DIR/std.pcm
-
-  cd $ROOT_DIR
+    cd $ROOT_DIR
 fi
 
 if ! [ -f $MODULES_DIR/std.compat.pcm ]; then
@@ -129,64 +129,64 @@ if ! [ -f $MODULES_DIR/std.compat.pcm ]; then
     std.compat.cppm                      \
     --precompile -o $MODULES_DIR/std.compat.pcm
 
-  cd $ROOT_DIR
+    cd $ROOT_DIR
 fi
 
 if ! [ -f $MODULES_DIR/dylib.pcm ]; then
-  cd $LIBCXX_MODULES_DIR/c++/v1
-  log_info "compiling dylib module..."
-
-  $CPP2B_COMPILER                        \
-    -stdlib=libc++                       \
-    -std=c++23                           \
-    -fexperimental-library               \
-    -isystem $LIBCXX_INCLUDE_DIR/c++/v1  \
-    -fprebuilt-module-path=$MODULES_DIR  \
-    "$ROOT_DIR/src/dylib.cppm"           \
-    --precompile -o $MODULES_DIR/dylib.pcm
+    cd $LIBCXX_MODULES_DIR/c++/v1
+    log_info "compiling dylib module..."
+
+    $CPP2B_COMPILER                        \
+        -stdlib=libc++                       \
+        -std=c++23                           \
+        -fexperimental-library               \
+        -isystem $LIBCXX_INCLUDE_DIR/c++/v1  \
+        -fprebuilt-module-path=$MODULES_DIR  \
+        "$ROOT_DIR/src/dylib.cppm"           \
+        --precompile -o $MODULES_DIR/dylib.pcm
 
-  cd $ROOT_DIR
+    cd $ROOT_DIR
 fi
 
 log_info "compiling cpp2b module..."
 if [ -f "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm" ]; then
-	rm "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm"
+    rm "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm"
 fi
 
 cat "$ROOT_DIR/share/cpp2b.cppm.tpl" | sed "s\`@CPP2B_PROJECT_ROOT@\`$ROOT_DIR\`g" > "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm"
 
-$CPP2B_COMPILER                                     \
-  -stdlib=libc++                                    \
-  -std=c++23                                        \
-  -fexperimental-library                            \
-  -isystem $LIBCXX_INCLUDE_DIR/c++/v1               \
-  -fprebuilt-module-path=$MODULES_DIR               \
-  "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm"  \
-  --precompile -o $MODULES_DIR/cpp2b.pcm
+$CPP2B_COMPILER                                       \
+    -stdlib=libc++                                    \
+    -std=c++23                                        \
+    -fexperimental-library                            \
+    -isystem $LIBCXX_INCLUDE_DIR/c++/v1               \
+    -fprebuilt-module-path=$MODULES_DIR               \
+    "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm"  \
+    --precompile -o $MODULES_DIR/cpp2b.pcm
 
 log_info "running cppfront..."
 $CPPFRONT src/main.cpp2 -pure -import-std -l -format-colon-errors -o "$ROOT_DIR/.cache/cpp2/source/src/main.cpp"
 
 log_info "compiling..."
-$CPP2B_COMPILER                                 \
-  -stdlib=libc++                                \
-  "$MODULES_DIR/cpp2b.pcm"                      \
-  "$MODULES_DIR/dylib.pcm"                      \
-  "$MODULES_DIR/std.compat.pcm"                 \
-  "$ROOT_DIR/.cache/cpp2/source/src/main.cpp"   \
-  -std=c++23                                    \
-  -fexperimental-library                        \
-  -Wno-unused-result                            \
-  -Wno-deprecated-declarations                  \
-  -fprebuilt-module-path=$MODULES_DIR           \
-  -L$LIBCXX_LIB_DIR                             \
-  -isystem $LIBCXX_INCLUDE_DIR/c++/v1           \
-  -lc++abi                                      \
-  -lc++                                         \
-  -lm                                           \
-  -static                                       \
-  -fuse-ld=lld                                  \
-  -I"$CPPFRONT_INCLUDE_DIR"                     \
-  -o $CPP2B_DIST
+$CPP2B_COMPILER                                   \
+    -stdlib=libc++                                \
+    "$MODULES_DIR/cpp2b.pcm"                      \
+    "$MODULES_DIR/dylib.pcm"                      \
+    "$MODULES_DIR/std.compat.pcm"                 \
+    "$ROOT_DIR/.cache/cpp2/source/src/main.cpp"   \
+    -std=c++23                                    \
+    -fexperimental-library                        \
+    -Wno-unused-result                            \
+    -Wno-deprecated-declarations                  \
+    -fprebuilt-module-path=$MODULES_DIR           \
+    -L$LIBCXX_LIB_DIR                             \
+    -isystem $LIBCXX_INCLUDE_DIR/c++/v1           \
+    -lc++abi                                      \
+    -lc++                                         \
+    -lm                                           \
+    -static                                       \
+    -fuse-ld=lld                                  \
+    -I"$CPPFRONT_INCLUDE_DIR"                     \
+    -o $CPP2B_DIST
 
 log_info "successfully built $CPP2B_DIST"
diff --git a/run.cmd b/run.cmd
index 45c3753..b568234 100644
--- a/run.cmd
+++ b/run.cmd
@@ -1,10 +1,10 @@
-@echo off
-
-set root_dir=%~dp0
-set cpp2b_dist=%~dp0dist\debug\cpp2b
-
-if not exist "%cpp2b_dist%.exe" (
-	call %~dp0build.cmd
-)
-
-"%cpp2b_dist%.exe" %*
+@echo off
+
+set root_dir=%~dp0
+set cpp2b_dist=%~dp0dist\debug\cpp2b
+
+if not exist "%cpp2b_dist%.exe" (
+    call %~dp0build.cmd
+)
+
+"%cpp2b_dist%.exe" %*
diff --git a/share/run_with_msvc_env.cmd b/share/run_with_msvc_env.cmd
index d736b2b..994a43b 100644
--- a/share/run_with_msvc_env.cmd
+++ b/share/run_with_msvc_env.cmd
@@ -3,16 +3,16 @@
 set vswhere="%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe"
 
 for /f "usebackq tokens=*" %%i in (`%vswhere% -latest -products * -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`) do (
-	set vs_install_dir=%%i
+    set vs_install_dir=%%i
 )
 
 if exist "%vs_install_dir%\VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt" (
-	set /p vs_tools_version=<"%vs_install_dir%\VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt"
+    set /p vs_tools_version=<"%vs_install_dir%\VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt"
 )
 
 if "%vs_tools_version%"=="" (
-	echo ERROR: cannot find VC tools installed on your system
-	exit 1
+    echo ERROR: cannot find VC tools installed on your system
+    exit 1
 )
 
 set vs_tools_dir=%vs_install_dir%\VC\Tools\MSVC\%vs_tools_version%
diff --git a/src/main.cpp2 b/src/main.cpp2
index f280a77..51b33db 100644
--- a/src/main.cpp2
+++ b/src/main.cpp2
@@ -103,6 +103,13 @@ module_source_extension: (compiler: cpp2b::compiler_type) -> std::string_view =
 	std::abort();
 }
 
+bmi_extension: (compiler: cpp2b::compiler_type) -> std::string_view = {
+	if compiler == cpp2b::compiler_type::msvc  { return ".ifc"; }
+	if compiler == cpp2b::compiler_type::clang { return ".pcm"; }
+	if compiler == cpp2b::compiler_type::gcc   { return ".pcm"; } // TODO: Is this right?
+	std::abort();
+}
+
 generate_cpp2b_module: () = {
 	cpp2b_module_template_path: fs::path = share_dir() / "cpp2b.cppm.tpl";
 	cpp2b_module_source_path: fs::path = ".cache/cpp2/source/_build/cpp2b(module_source_extension(cpp2b::compiler()))$";
@@ -171,22 +178,46 @@ get_vs_tools_dir: () -> fs::path = {
 	return getenv_sv("VCToolsInstallDir").expect("missing 'VCToolsInstallDir' environment variable");
 }
 
-ensure_std_modules: () = {
-	d := modules_dir();
-	std_bmi: fs::path = d / "std.ifc";
-	std_compat_bmi: fs::path = d / "std.compat.ifc";
-	vs_tools_dir := get_vs_tools_dir();
+get_libcxx_build_root: () -> fs::path = {
+	return getenv_sv("CPP2B_LIBCXX_BUILD_ROOT").expect("missing 'CPP2B_LIBCXX_BUILD_ROOT' environment variable");
+}
 
-	if !fs::exists(std_bmi) {
-		build_cpp1_module("std", :std::vector=(vs_tools_dir / "modules" / "std.ixx"), :std::vector<std::string> = ());
-	}
+get_system_modules_dir: (compiler: cpp2b::compiler_type) -> fs::path = {
+	if compiler == cpp2b::compiler_type::msvc  { return get_vs_tools_dir() / "modules"; }
+	if compiler == cpp2b::compiler_type::clang { return get_libcxx_build_root() / "modules"; }
+	log_error("cannot find system cpp20 modules directory");
+	std::abort();
+}
+
+ensure_system_module: (name: std::string) = {
+	ensure_system_module(name, :std::vector<std::string> = ());
+}
 
-	if !fs::exists(std_compat_bmi) {
-		build_cpp1_module("std.compat", :std::vector=(vs_tools_dir / "modules" / "std.compat.ixx"), :std::vector=("std"));
+ensure_system_module: (name: std::string, deps) = {
+	d := modules_dir();
+	bmi := d / std::format("{}{}", name, bmi_extension(cpp2b::compiler()));
+	system_modules_dir := get_system_modules_dir(cpp2b::compiler());
+
+	if !fs::exists(bmi) {
+		build_cpp1_module(
+			name,
+			:std::vector=(system_modules_dir / std::format("{}{}", name, module_source_extension(cpp2b::compiler()))),
+			deps
+		);
 	}
 }
 
+ensure_std_modules: () = {
+	ensure_system_module("std");
+	ensure_system_module("std.compat", :std::vector=("std"));
+}
+
 build_cpp1_module: (name: std::string, sources, module_deps) = {
+	if cpp2b::compiler() != cpp2b::compiler_type::msvc {
+		log_error("TODO: build_cpp1_module non-msvc support");
+		std::abort();
+	}
+
 	d := fs::absolute(modules_dir());
 	bmi := d / ("(name)$.ifc");
 	cmd_str: std::string = "cl /nologo /std:c++latest /W4 /MDd /EHsc /c /interface /TP";
@@ -469,6 +500,11 @@ build_binary: (info: cpp2b_source_binary_info) -> build_binary_result = {
 	ensure_dir(log_path.parent_path());
 	ensure_dir(bin_outpath.parent_path());
 
+	if cpp2b::compiler() != cpp2b::compiler_type::msvc {
+		log_error("TODO: build_binary non-msvc support");
+		std::abort();
+	}
+
 	d := fs::absolute(modules_dir());
 	cmd_str: std::string = "cl /nologo /std:c++latest /W4 /MDd /EHsc /DEBUG:full /Zi /FC";
 	for info.imports do (imp: std::string) {
@@ -521,6 +557,11 @@ build_build_script: (info: cpp2b_source_build_info) -> build_binary_result = {
 	ensure_dir(log_path.parent_path());
 	ensure_dir(bin_outpath.parent_path());
 
+	if cpp2b::compiler() != cpp2b::compiler_type::msvc {
+		log_error("TODO: build_build_script non-msvc support");
+		std::abort();
+	}
+
 	d := fs::absolute(modules_dir());
 	cmd_str: std::string = "cl /nologo /std:c++latest /W4 /MDd /EHsc /LDd /DLL";
 	for info.imports do (imp: std::string) {