code: def add_f90_to_env(env):
      
      try:
          F90Suffixes = env['F90FILESUFFIXES']
      except KeyError:
          F90Suffixes = ['.f90']
  
      #print("Adding %s to f90 suffixes" % F90Suffixes)
      try:
          F90PPSuffixes = env['F90PPFILESUFFIXES']
      except KeyError:
          F90PPSuffixes = []
  
      DialectAddToEnv(env, "F90", F90Suffixes, F90PPSuffixes,
                      support_module = 1)
docs: Add Builders and construction variables for f90 to an Environment.