function, i.e., can be passed to @code{funcall}. Note that
@code{functionp} returns @code{t} for symbols that are function names,
and returns @code{nil} for special forms.
+@end defun
+
+ It is also possible to find out how many arguments an arbitrary
+function expects:
+
+@defun func-arity function
+This function provides information about the argument list of the
+specified @var{function}. The returned value is a cons cell of the
+form @w{@code{(@var{min} . @var{max})}}, where @var{min} is the
+minimum number of arguments, and @var{max} is either the maximum
+number of arguments, or the symbol @code{many} for functions with
+@code{&rest} arguments, or the symbol @code{unevalled} if
+@var{function} is a special form.
+
+Note that this function might return inaccurate results in some
+situations, such as the following:
+
+@itemize @minus
+@item
+Functions defined using @code{apply-partially} (@pxref{Calling
+Functions, apply-partially}).
+
+@item
+Functions that are advised using @code{advice-add} (@pxref{Advising
+Named Functions}).
+
+@item
+Functions that determine the argument list dynamically, as part of
+their code.
+@end itemize
+
@end defun
@noindent
@end defun
@defun subr-arity subr
-This function provides information about the argument list of a
-primitive, @var{subr}. The returned value is a pair
-@code{(@var{min} . @var{max})}. @var{min} is the minimum number of
-args. @var{max} is the maximum number or the symbol @code{many}, for a
-function with @code{&rest} arguments, or the symbol @code{unevalled} if
-@var{subr} is a special form.
+This works like @code{func-arity}, but only for built-in functions and
+without symbol indirection. It signals an error for non-built-in
+functions. We recommend to use @code{func-arity} instead.
@end defun
@node Lambda Expressions
static Lisp_Object funcall_lambda (Lisp_Object, ptrdiff_t, Lisp_Object *);
static Lisp_Object apply_lambda (Lisp_Object, Lisp_Object, ptrdiff_t);
+static Lisp_Object lambda_arity (Lisp_Object);
static Lisp_Object
specpdl_symbol (union specbinding *pdl)
return unbind_to (count, val);
}
+DEFUN ("func-arity", Ffunc_arity, Sfunc_arity, 1, 1, 0,
+ doc: /* 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. */)
+ (Lisp_Object function)
+{
+ Lisp_Object original;
+ Lisp_Object funcar;
+ Lisp_Object result;
+ short minargs, maxargs;
+
+ original = function;
+
+ retry:
+
+ /* Optimize for no indirection. */
+ function = original;
+ if (SYMBOLP (function) && !NILP (function)
+ && (function = XSYMBOL (function)->function, SYMBOLP (function)))
+ function = indirect_function (function);
+
+ if (SUBRP (function))
+ result = Fsubr_arity (function);
+ else if (COMPILEDP (function))
+ result = lambda_arity (function);
+ 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)
+ || EQ (funcar, Qclosure))
+ result = lambda_arity (function);
+ else if (EQ (funcar, Qautoload))
+ {
+ Fautoload_do_load (function, original, Qnil);
+ goto retry;
+ }
+ else
+ xsignal1 (Qinvalid_function, original);
+ }
+ return result;
+}
+
+/* FUN must be either a lambda-expression or a compiled-code object. */
+static Lisp_Object
+lambda_arity (Lisp_Object fun)
+{
+ Lisp_Object val, syms_left, next;
+ ptrdiff_t minargs, maxargs;
+ bool optional;
+
+ if (CONSP (fun))
+ {
+ if (EQ (XCAR (fun), Qclosure))
+ {
+ fun = XCDR (fun); /* Drop `closure'. */
+ CHECK_LIST_CONS (fun, fun);
+ }
+ syms_left = XCDR (fun);
+ if (CONSP (syms_left))
+ syms_left = XCAR (syms_left);
+ else
+ xsignal1 (Qinvalid_function, fun);
+ }
+ else if (COMPILEDP (fun))
+ {
+ ptrdiff_t size = ASIZE (fun) & PSEUDOVECTOR_SIZE_MASK;
+ if (size <= COMPILED_STACK_DEPTH)
+ xsignal1 (Qinvalid_function, fun);
+ syms_left = AREF (fun, COMPILED_ARGLIST);
+ if (INTEGERP (syms_left))
+ return get_byte_code_arity (syms_left);
+ }
+ else
+ emacs_abort ();
+
+ minargs = maxargs = optional = 0;
+ for (; CONSP (syms_left); syms_left = XCDR (syms_left))
+ {
+ next = XCAR (syms_left);
+ if (!SYMBOLP (next))
+ xsignal1 (Qinvalid_function, fun);
+
+ if (EQ (next, Qand_rest))
+ return Fcons (make_number (minargs), Qmany);
+ else if (EQ (next, Qand_optional))
+ optional = 1;
+ else
+ {
+ if (!optional)
+ minargs++;
+ maxargs++;
+ }
+ }
+
+ if (!NILP (syms_left))
+ xsignal1 (Qinvalid_function, fun);
+
+ return Fcons (make_number (minargs), make_number (maxargs));
+}
+
+
DEFUN ("fetch-bytecode", Ffetch_bytecode, Sfetch_bytecode,
1, 1, 0,
doc: /* If byte-compiled OBJECT is lazy-loaded, fetch it now. */)
defsubr (&Seval);
defsubr (&Sapply);
defsubr (&Sfuncall);
+ defsubr (&Sfunc_arity);
defsubr (&Srun_hooks);
defsubr (&Srun_hook_with_args);
defsubr (&Srun_hook_with_args_until_success);