David Kastrup wrote:
Kevin Rodgers <[EMAIL PROTECTED]> writes:
Alan Mackenzie wrote:
Is it possible to determine at run time how many parameters an elisp
function takes? For example, I'd like to write something like:
(how-many-params 'null)
and have it evaluate to 1. Or something like that. Together with
some
reasonable convention for indicating &optional and &rest arguments.
I would start with eldoc-function-arglist.
For built-in functions, subr-arity might help.
And now for lisp functions, lambda-arity:
(require 'eldoc)
(defun lambda-arity (function)
"Return minimum and maximum number of args allowed for FUNCTION.
FUNCTION must be a symbol whose function binding is a lambda expression
or a macro.
The returned value is a pair (MIN . MAX). MIN is the minimum number
of args. MAX is the maximum number or the symbol `many', for a lambda
or macro with `&rest' args."
(let* ((arglist (eldoc-function-arglist function))
(optional-arglist (memq '&optional arglist))
(rest-arglist (memq '&rest arglist)))
(cons (- (length arglist)
(cond (optional-arglist (length optional-arglist))
(rest-arglist (length rest-arglist))
(t 0)))
(cond (rest-arglist 'many)
(optional-arglist (+ (length arglist)
(length optional-arglist)
-1))
(t (length arglist))))))
--
Kevin Rodgers
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