Can I write a DLL file that export some functions use the common lisp?

Question

Can I write a DLL file that export some functions use the common lisp?Thank you!

Answer 1

Each Common Lisp implementation has a different way to extend it from various foreign languages. Which implementation do you intend to use?

The GNU CLISP implementation allows one to define external modules written in C that expose objects, symbols, and functions to Lisp. The documentation for writing an external module is complete, but you'll likely find it difficult to integrate this into the rest of your build process, unless you're already using make or shell scripts to automate portions of it.

Alternately, you can turn the question around and ask how do you access C libraries from Common Lisp. Again, most implementations have a foreign function interface, or FFI that allows them to reach out to various other languages. CLISP has an FFI, but you can also use a package like CFFI for portability among Common Lisp implementations. The CLISP documentation describes the trades in these two approaches.

ECL may be another good choice for you if you intend to embed Common Lisp within your C program.

Answer 2

(..i'm not 100% sure what you mean, but i'll just throw some bits out there and see what happens..)

Most Lisps can do the C <--> Lisp type thing by ways of FFI, and there are compatibility layers/libraries for doing FFI like the already mentioned CFFI.

So you can pretty much always have Lisp call C functions and have C call Lisp functions, and most do it by loading .dll/.so files into the already running Lisp process. Note that this tends to be what other environments like Python (PyGTK etc.) do too. This is often exactly what you want, so you might perhaps want to ignore most of what I say below.

The only Lisp I can think of that enables one to do things the "other way around", i.e., load a .dll/.so which "is" Lisp or is produced by Lisp into an already running C process, is ECL.

In many cases it really does not matter where you put the entry point or the "main() function" to use C terms, so if you'd like to use some other Lisp besides ECL but are thinking you "can't because .." this is something to reconsider since, yeah, you can in many cases just shuffle thing around a bit.

However, it's almost always a much better idea to user other IPC mechanisms and avoid any kind of FFI when you can.