docs: def function_invocation_proxy(fn, proxy_args, proxy_kwargs):
          """execute the fuction if it is one, else evaluate the fn as a boolean
          and return that value.
  
          Sometimes rather than providing a predicate, we just give the value of
          True.  This is shorthand for writing a predicate that always returns
          true."""
          try:
              return fn(*proxy_args, **proxy_kwargs)
          except TypeError:
              return bool(fn)