writing an elisp interface to a c library

writing an elisp interface to a c library

[James Cloos]

Can anyone point me to a good example in the emacs codebase of a lisp
api that closely matches an existing external c api?  So far I've only
hacked the elisp part of emacs, not the C....

I presume I'll need to create some read-only lisp integers matching
the names of the various enum values, lisp objects to hold the (opaque)
structs the lib uses and DEFUNs to match the lib's api?  I have read
the primitives section of the elisp manual, but which src files are
the best to study?  

(As I see it, the lib's api is such that it can be mapped to lisp w/o
diverging from its C look and feel.  Following that api very closely,
then, seems to be the Right Thing To Do.  Being able to write all of
the higher-level code using the lib in elisp is enticing.)

I'm primarily targetting the emacs-unicode-2 branch for this project,
if it makes any difference.

Thanks,

-JimC
-- 
James H. Cloos, Jr. <cloos@jhcloos.com>

Re: writing an elisp interface to a c library

[Masatake YAMATO]

> Can anyone point me to a good example in the emacs codebase of a lisp
> api that closely matches an existing external c api?  So far I've only
> hacked the elisp part of emacs, not the C....
> 
> I presume I'll need to create some read-only lisp integers matching
> the names of the various enum values, lisp objects to hold the (opaque)
> structs the lib uses and DEFUNs to match the lib's api?  I have read
> the primitives section of the elisp manual, but which src files are
> the best to study?  

I don't know well about the C side. However, I think M-x describe-function
on a built-in function is really helpful. Because its *Help* buffer
contains a link to its definition in a C source file.

Try "M-x describe-function car" to know about list.
Try "M-x describe-function to numberp" to know about number...

I feel strong GNU'ism from the link.

Masatake YAMATO

Re: writing an elisp interface to a c library

[Thien-Thi Nguyen]

James Cloos <cloos@jhcloos.com> writes:

> (As I see it, the lib's api is such that it can be mapped to lisp w/o
> diverging from its C look and feel.  Following that api very closely,
> then, seems to be the Right Thing To Do.  Being able to write all of
> the higher-level code using the lib in elisp is enticing.)

how close/far/easy/difficult it is depends on the C library's interface.
check out http://www.swig.org for an interface mapping mux approach.
it would be cool to see an emacs lisp module for swig.

thi

Re: writing an elisp interface to a c library

[James Cloos]

For the archives, src/xfaces.c is a good example to look at after
reading the relevant sections of the elisp manual.  

I browsed through all of src; of all of the .c files, xfaces.c
deals with an api most similar to what I asked about.

-JimC
-- 
James H. Cloos, Jr. <cloos@jhcloos.com>