[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Functions returning functions in Emacs Lisp
From: |
srinik001 |
Subject: |
Functions returning functions in Emacs Lisp |
Date: |
Tue, 15 Apr 2008 20:18:09 -0700 (PDT) |
User-agent: |
G2/1.0 |
Hi,
I am trying to learn Emacs Lisp. I know a bit of (Common) Lisp and was
trying the following on Emacs. This is to define a function called
derivative, which returns as its result a function which is the
derivative of the argument function fn, when the numerical calculation
is done over delta. So I did the following.
(defun derivative (fn delta)
#'(lambda(x) (/ (- (funcall fn (+ x delta)) (funcall fn x)) delta)))
--> this seemed to work (i.e. no error on C-x C-e)
(setq c (derivative #'sin 0.001))
--> this seemed to work (again, no error on evaluation)
(funcall c (/ 3.1415 2))
--> this threw up an error. The error is the following:
Debugger entered--Lisp error: (void-variable fn)
(funcall fn (+ x delta))
(- (funcall fn (+ x delta)) (funcall fn x))
(/ (- (funcall fn ...) (funcall fn x)) delta)
(lambda (x) (/ (- ... ...) delta))(1.57075)
funcall((lambda (x) (/ (- ... ...) delta)) 1.57075)
eval((funcall c (/ 3.1415 2)))
eval-last-sexp-1(nil)
eval-last-sexp(nil)
call-interactively(eval-last-sexp)
I tried lambda expressions on mapcar, and it seemed to work on Emacs
the way it does in Common Lisp. Could someone please tell me if I am
doing something wrong vis-a-vis Emacs, or if Emacs does not support
this? Thanks.
Regards,
SK
- Functions returning functions in Emacs Lisp,
srinik001 <=