Re: Programmatically creating functions

[Ian Eure]

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