Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcvax!ukc!warwick!csuwn
From: csuwn@cu.warwick.ac.uk (Max)
Newsgroups: comp.emacs
Subject: apply, mapcar, lack of setenv
Keywords: Emacs-lisp, hacking, environment
Message-ID: <CSUWN.89Jun2041413@orchid.warwick.ac.uk>
Date: 2 Jun 89 03:14:13 GMT
Sender: csuwn@warwick.ac.uk
Distribution: comp
Organization: Computing Services, Warwick University, UK
Lines: 83


I have just started working with emacs-lisp having some exprience with
Franz Lisp. Without the manuals finding out about functions and
variables is a long boring process of searching the respective entire
completions, or other standard libries.

So far all has gone well, I found out how to create processes, and set
sentinels to watch over them. However in some cases some things seem
not to work as expected - or infact are not included in emacs.

1: Apply, and mapcar

I frequently want to do the following;

(apply 'or (mapcar 'function list)) where function returns t or nil.

Problem: Apply dosent know about the function or.
Solution:

(cond ((<= 1 (apply '+ (mapcar 'nfunction list))) t)
      (t nil))

Where nfunction returns 1 or 0 instead of t or nil respectively.

Is there a more elegant solution, or am I perhaps missing something.
Also why no lambda function in emacs (is it that hard to implement),
as its use with mapcar makes life so much easier.

(I know e-lisp is not supposed to be like lisp - but old habits die
hard.)

2: setenv

I was writing some code - and I needed to change the environment of
emacs just before starting a new sub-process. I found the function
getenv - but the partner setenv just did not seem to exist!!

A quick perusal of the variables gave me process-environment - a list
of environment strings which will be used by subprocesses.

It seemed silly not to have a setenv so I wrote one myself.
Notice how the apply/mapcar/or/lambda function makes life so much harder!
I would appreciate knowledgable insights into modifications to make
the code more elegant.

;;------ Cut here 8< --------------------------------------------------

(defun setenv (name new)
  (cond ((<= 1 (apply '+ (mapcar 'env-entry process-environment)))
	;;The process-environment list contains the name - therefore
	;;change it to the new value
	 (setq proccess-environment (mapcar 'change-env
					    process-environment)))
	(t 
	;;Otherwise just append the new setting to the front of the list.
	 (setq process-environment
		 (append (list (format "%s=%s" name new))
			 process-environment)))))

(defun change-env (str)
    ;;Return the new setting of the environment if str contains the
    ;;old setting, otherwise just returning str.
    (cond ((= 1 (env-entry str))
	   (format "%s=%s" name new))
	  (t str)))

(defun env-entry (entry)
    ;;Does entry contain the environment variable name?
    ;;Return 1 if it does - 0 otherwise
  (let ((match (string-match (format "%s=" name) entry)))
    (cond ((null match) 0)
	  ((= match 0) 1)
	  (t 0))))

;;----------------------------------------------------------------------

	Thanks for your time, 

--
NAME : H J "Max" Thompson -  So called for I Max And Xian.
SNAIL: Department Of Computer Science, Warwick University, CV4 7AL, ENGLAND.
JANET: max@cs.warwick.ac.uk               UUCP: {uunet,mcvax}!ukc!warwick!max
JOKE : "Waiter there's a fly in my soup!" "Sir, Its a feature not a bug!"