Re: Calling different kinds of functions, which finish the same job

[Kevin Rodgers <ihs_4664@yahoo.com>]

Herbert Euler wrote:
>> From: Kevin Rodgers <ihs_4664@yahoo.com>
>> To: help-gnu-emacs@gnu.org
>> Subject: Re: Calling different kinds of functions, which finish the 
>> same job
>> Date: Tue, 11 Apr 2006 09:49:29 -0600
>>
>> [This doesn't belong on emacs-devel]
> 
> 
> OK.  Sorry for having sent to emacs-devel.
> 
>> What are "args of f1" etc?  They are apparently not the arguments to a 
>> single call to f1, since you have these variations:
>>
>> (apply ,func) ; this is tried first
>> (apply ,func (car ,largs)) ; then this is tried, while cdr'ing down largs
>>
>> If all of the functions are defined, why would any of the function 
>> call signal an error?  Why do you care which function is actually called?
>> You certainly don't return that information, you only return the 
>> result of the first non-error-signalling call.
> 
> 
> Suppose functions f1, f2, and f3 are all for inserting one space, but
> without side effect or with different side effect;  f1 requires an
> integeral argument as count, f2 requires an symbolic argument specifies
> how the side effect is caused, and f3 requires two arguments, one
> of them is an integer, the other one is a symbol.  Now, if I want to
> insert one space (either with or without side effect), I can issue one
> of the following commands:
> 
>    (f1 1)
>    (f2 'indent)
>    (f3 1 'indent)
> 
> And I'm granteed that, if one space is inserted, one of f1, f2, f3 is
> called, but I don't which one is called.  So I want I can write (with
> function in my last post),
> 
>    (xgp-casi2-safe-call f '((1) (indent) (1 indent)))
 >
> Where f is one of f1, f2, or f3 (got from environment).

No you can't, because your macros call

(f1)
(f1 1)
(f2)
(f2 indent)
(f3)
(f3 1)
(f3 indent)

> If f can be
> self-insert-command as well, the first trial will be successful  (so
> perhaps I should make invoking without arguments the last trial).
> 
> Any better solutions?  Thanks.

(condition-case nil
     (f1 1)
   (error (condition-case nil
              (f2 'indent)
            (error (f3 1 'indent)))))

(defmacro try (&rest forms)
   "Eval FORMS until one of them returns without signalling an error."
   `(condition-case nil
        ,(car forms)
      (error (try ,@(cdr forms)))))

(try (f1 1) (f2 'indent) (f3 1 'indent))

-- 
Kevin Rodgers