The function would basically do this. We should replace all the other cases were we check the flags directly. ``` function(hal_check_env VAR_NAME) if(NOT DEFINED ENV{${VAR_NAME}}) message(FATAL_ERROR "Build environment variable ${VAR_NAME} is required for this project.") endif() endfunction() check_env(LIBHAL_PLATFORM_LIBRARY) check_env(LIBHAL_PLATFORM) ```