Re: Programmatically creating functions

[Ian Eure <ian@digg.com>]

On Oct 21, 2008, at 11:57 AM, Andreas Politz wrote:

> Joost Diepenmaat wrote:
>> Ian Eure <ian@digg.com> writes:
>>> So, I have a list of symbols:
>>>
>>> '(foo bar baz)
>>>
>>> I want to iterate over the list and create a function from each  
>>> which
>>> does something like this:
>>>
>>> (defun call-foo ()
>>>  (interactive)
>>>  (invoke-stuff 'foo)
>>>
>>> How can I accomplish this? I can't figure out how to create the
>>> function. I've tried a number of approaches, but have not met with
>>> success.
>>>
>>> - eval'ing the defun. Returns a function symbol, but I can't call
>>> it. Maybe it's only created within the scope of the (eval) and not
>>> callable from outside?
>>>
>>> - Creating a symbol and using fset to assign a lambda to it's
>>> function cell. It sort of works, but I'm unclear on how to pass a
>>> variable function name to defun, nor am I clear on how I can make  
>>> sure
>>> it calls invoke-stuff with the right symbol.
>> I'm not /quite/ sure where you've got problems, but in this case  
>> elisp's
>> lack of closures hurts. IMHO the simplest way to get what you want  
>> is to
>> use a macro:
>> (defmacro make-caller-macro (symbol)   `(defun ,(intern (concat  
>> "call-" (symbol-name symbol))) ()      (,symbol)))
>> But that won't evaluate the argument, so you'd more or less have to  
>> use
>> eval as well:
>> (dolist (s '(foo bar)) (eval `(make-caller-macro ,s)))
>
>
> Does this work ? (in general)
>
Yes, with a little hacking, it works:

(defvar sql-connection-alist
   '((poola
      (sql-product 'mysql)
      (sql-server "pool-a")
      (sql-user "me")
      (sql-password "mypass")
      (sql-database "default")
      (sql-port 3306))
     (poolb
      (sql-product 'mysql)
      (sql-server "pool-b")
      (sql-user "me")
      (sql-password "mypass")
      (sql-database "default")
      (sql-port 3307)))
   "AList of preset connections for `sql-connect-preset'.")

(defun sql-connect-preset (name)
   "Connect to a predefined SQL connection listed in `sql-connection- 
alist'"
   (require 'sql)
   (let ((conn (cdr (assoc name sql-connection-alist)))
         (sql-name (symbol-name name)))
     (eval `(let ,conn
              (flet ((sql-get-login (&rest what)))
                (sql-product-interactive sql-product))))))

(defun sql-convenience ()
   (interactive)
   (mapcar (lambda (conn)
             (let ((name (car conn)))
               (fset (intern (format "sql-%s" name))
                     `(lambda nil
                        ,(format "Connect to %s SQL preset." name)
                        (interactive)
                        (sql-connect-preset ',name)))))
           sql-connection-alist))

So now I can define preset connections and get sql-* methods to invoke  
them directly.

Thank you for the help.

  - Ian