Is it possible to write a Windows DLL in Red?

Question

I'd like to write a plugin for some Windows application, and it must be a DLL. I'd really love to try doing it in a mix of Red & Red/System. But asking on Rebol&Red chatroom here on SO, I got mixed responses as to whether it is currently possible in both Red and Red/System, or in Red/System only. What's the definitive answer?

Anomalism

Why oh why the downvote? Could you please comment, so that I could improve, or at least understand? I can never understand how people can just cast a first vote as downvote and not care to comment to help the author. – Anomalism

Answer 1

Yes, it is possible. You can check the announcement on the Red-Blog for 0.3.3

First of all, here is a short snippet describing the process for Red/System:

Shared lib generation

Since a year, we were working on bringing shared library generation, now it is available in the main branch. New features were added to support library generation like a way to declare the exported symbols and special callback functions when loading and freeing the library. Here is a simple example of a Red/System library:

Red/System [
    File: %testlib.reds
]

inc: func [n [integer!] return: [integer!]][n + 1] 

#export [inc]

You compile such shared library using the new -dlib command-line option:

do/args %rsc.r "-dlib testlib.reds"

The output binary name will have a platform-specifc suffix (.dll, .so or .dylib).

Secondly, I was finally able to get a single simple Red script to compile to a .dll. The #export directive needs to be in a Red/System context as you can see the #system-global directive provides. Any function you have in Red needs to be wrapped with a Red/System wrapper. You can do this using #call as done below:

Red []    

hello: does [print "hello"]    

#system-global [
        hellosystem: does [
            #call [hello]
        ]    

        #export cdecl [hellosystem]
]

Crownwork

added another example – Crownwork

A Red/System sample works, but I was already told so on the chat, as I tried to explain. The other sample, when trying to compile with red.exe -dlib example.red, doesn't succeed with error "Loading Error", with id: 'cannot-open and arg1: "/C/prog/nppScripts/nppScripts03red/extension.reds". Could it compile without Rebol and extension.reds? – Anomalism

This method is not so straight forward if the arguments and return values are anything other than integer or logic. For example. you have to manage the conversion between a c-string! and a string! in the Red/System code. – Brozak

That makes sense. That is another good QA question. Thank you! – Crownwork

I renamed hello-system to hellosystem, because I'm not quite sure names with dash are allowed in DLLs; it compiled, but when I try to open the DLL, I'm getting an error: Failed to load testdll.dll: Invalid access to memory location. – Anomalism

Turns out the print statement may not output to the Right place on windows. I've successfully called the function from the dll in rebol but get no output, Not sure about the invalid access from Ruby. I have been traveling but will try to get a working example that returns a value for you when I get back home. You can take a look at getting the value from CALL here static.red-lang.org/red-system-specs.html#section-15.8 – Crownwork

If someone else more knowledgable could answer it would be better. – Crownwork

I asked on the Red mailing list, and I was told to try loading the DLL from C, and it worked! So, big thanks for your help, @kealist! Although, there does seem to happen something fishy indeed, if we're both having problems in non-C languages (I had my problems when loading from Go). – Anomalism