Path: utzoo!utgpu!attcan!uunet!pilchuck!dataio!uw-entropy!uw-june!whaley
From: whaley@june.cs.washington.edu (Ken Whaley)
Newsgroups: comp.lang.lisp
Subject: Re: foreign functions to KCL
Summary: Good news and Bad news.
Message-ID: <6381@june.cs.washington.edu>
Date: 10 Nov 88 06:08:38 GMT
References: <5363@medusa.cs.purdue.edu>
Reply-To: whaley@uw-june.UUCP (Ken Whaley)
Organization: U of Washington, Computer Science, Seattle
Lines: 62


The good news is that it's easy to incorporate C functions into
KCL.  The bad news is that unless you want to write C code that can't
be used outside of the KCL environment, then you are constrained to use
certain input parameter and function return types.  I don't purport to be an
expert on KCL -- this is just what I figured out from playing around with the
system.  By the way, I'm working with the "June 3, 1987" version of KCL.

As an example of how to use C code from KCL, let's write the square function
(that takes an integer argument and returns its square) in C, and foreign
function it into KCL.

Let's call the C function "c_square", and the LISP function "square".

:NOTE:  
The KCL documentation says that the following is specific to the BSD version
of KCL.

1. Create a file called "square.lsp" that consists of the line:

	(defentry square (int) (int c_square))
Argument 1 type------------^
Return type----------------------^
Name of C function in C source file-----^

(Other types that I know work are: char, double.  I imagine that any
"one-work" type should work.

2. Create the C file, say c_square.c:
	
	int c_square (x) int x; { return (x * x); } 

3. In KCL, type (compile-file "square").

4. Compile the C file from the shell (cc -c -O c_square.c)

5. In KCL, now type (si:faslink "square.o" "c_square.o")

6. You're in business.

	(square 7) ==> 49

	Note that the second string in step 5 is passed
	directly to "ld", so you can include other libraries (I don't believe
	that the C library is automatically included for you, so if you use
	any C library routines, you'll have to write the following
	for step 5): (si:faslink "square.o" "c_square.o -lc").

BTW, this information in included in the "doc/kclunix" file of the KCL
distribution.

Oh, and I've only managed to get this working with non-pointer types.
I haven't experimented with structs, either.  You can pass in, manipulate,
and return arbitrary LISP objects (KCL itself is written in C....), but
that sort of information is, as far as I know, undocumented, and you'd
have to dig through the source code to figure it out.

			Ken

						     
-- 
whaley@june.cs.washington.edu