Re: Optimising Elisp code

[Barry Margolin <barmar@alum.mit.edu>]

In article <638fb7dc-6fc5-4645-8793-97a00038a3a8@googlegroups.com>,
 Davin Pearson <davin.pearson@gmail.com> wrote:

> Suppose that you have a function:
> 
> (defun foo ()
>    (bar))
> 
> And bar is a function that has no side effects and returns 123 then calling
> the function code-optimize (the name of my optimisation routine)
> 
> M-x code-optimize on the function foo will result in the following defun 
> 
> (defun foo ()
>     123)

What you're describing is called inline expansion. AFAIK, the Elisp 
compiler doesn't do this automatically.

You can define bar as a macro -- those HAVE to be expanded at compile 
time, since that's how they work.

You can also define an inline function using defsubst. From the Elisp 
manual:

An inline function works just like an ordinary function except for one 
thing: when you compile a call to the function, the function's 
definition is open-coded into the caller.

Making a function inline makes explicit calls run faster. But it also 
has disadvantages. For one thing, it reduces flexibility; if you change 
the definition of the function, calls already inlined still use the old 
definition until you recompile them.

There are more caveats given in the documentation.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***