[Visionaries] The DG-Scheme Foreign Language Interface

[Peter Minten]

Hi folks,

I've found a way to build the Foreign Language Interface without depending on 
the FLI interface of the language the interpreter is written in. Here's a diagram:

+---------------------+          +------------------------+
|     FLI wrapper     |   pipe   |    DGS interpreter     |
|  +---------------+  | <------> |  +------------------+  |
|  |  foreign lib  |  |          |  |  DG-Scheme code  |  |
|  +---------------+  |          |  +------------------+  |
+---------------------+          +------------------------+

The FLI wrapper is a separate process and writen in an appropriate language for 
calling the foreign lib. The FLI wrapper loads the foreign lib. When the DGS 
interpreter, at the command of the DGS code, send a function call the FLI 
wrapper reads it and calls the right function. Then the FLI wrapper sends back 
the result.

The protocol used is a custom binary DG-Scheme FLI protocol. Since binary 
protocols are fast and this protocol is not meant to be used for anything else 
than DG-Scheme FLI I consider it the best option.

The protocol is pretty advanced, supporting stuff like objects. However it's 
DGS-centric, the FLI wrapper translates the DGS into the foreign language and back.

The advantage of this scheme is that I can basically call any language with one 
FLI protocol, all you need is a FLI wrapper for the language you want to call.

Greetings,

Peter