Function: func-arity

func-arity is a function defined in eval.c.

Signature

(func-arity FUNCTION)

Documentation

Return minimum and maximum number of args allowed for FUNCTION.

FUNCTION must be a function of some kind. The returned value is a cons cell (MIN . MAX). MIN is the minimum number of args. MAX is the maximum number, or the symbol many, for a function with &rest args, or unevalled for a special form.

Note that this function might return inaccurate results in some cases, such as with functions defined using apply-partially, functions advised using advice-add, and functions that determine their arg list dynamically.

View in manual

Probably introduced at or before Emacs version 26.1.

Source Code

// Defined in /usr/src/emacs/src/eval.c
{
  Lisp_Object original;
  Lisp_Object funcar;
  Lisp_Object result;

  original = function;

 retry:

  /* Optimize for no indirection.  */
  function = original;
  if (SYMBOLP (function) && !NILP (function))
    {
      function = XSYMBOL (function)->u.s.function;
      if (SYMBOLP (function))
	function = indirect_function (function);
    }

  if (CONSP (function) && EQ (XCAR (function), Qmacro))
    function = XCDR (function);

  if (SUBRP (function))
    result = Fsubr_arity (function);
  else if (CLOSUREP (function))
    result = lambda_arity (function);
#ifdef HAVE_MODULES
  else if (MODULE_FUNCTIONP (function))
    result = module_function_arity (XMODULE_FUNCTION (function));
#endif
  else
    {
      if (NILP (function))
	xsignal1 (Qvoid_function, original);
      if (!CONSP (function))
	xsignal1 (Qinvalid_function, original);
      funcar = XCAR (function);
      if (!SYMBOLP (funcar))
	xsignal1 (Qinvalid_function, original);
      if (EQ (funcar, Qlambda))
	result = lambda_arity (function);
      else if (EQ (funcar, Qautoload))
	{
	  Fautoload_do_load (function, original, Qnil);
	  goto retry;
	}
      else
	xsignal1 (Qinvalid_function, original);
    }
  return result;
}