build.sh

#
# clean up any existing artifacts
#
rm -rf build/dist
mkdir -p build/dist >/dev/null 2>&1

#
# compile a module
#
clang++ -std=c++2a \
  -c hello.cxx \
  -fmodules \
  -Xclang -emit-module-interface \
  -o build/hello.pcm

#
# compile the code that uses it
#
clang++ -std=c++2a \
  -fmodules \
  -fprebuilt-module-path=build \
  main.cxx \
  hello.cxx \
  -o build/dist/hello \
  -fmodule-file=helloworld=build/hello.pcm

#
# run it
#
./build/dist/hello

hello.cxx

export module helloworld;

export namespace helloworld {
  auto hello () {
    return "Hello, world";
  }
}

main.cxx

import <iostream>;
import helloworld;

int main() {
  std::cout << helloworld::hello() << std::endl;
  return 0;
}