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dynamic foreign function interface

From: Andy Wingo
Subject: dynamic foreign function interface
Date: Tue, 26 Jan 2010 23:06:07 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)

Hey all,

I just finished up some work to make a dynamic foreign function
interface. This is on the wip-ffi branch.

By "dynamic", I mean that you don't have to write C and compile it; you
can do everything at runtime from Scheme. You use dynamic-func and
dynamic-link to get the raw function pointer, and make-foreign-function
to turn that function pointer into a Scheme procedure.

The interface is very low-level. Obviously declaring that an arbitrary
symbol resolved via `dlsym' is of a certain function type is an unsafe
operation that can lead to crashes.

Apart from that typing problem, you have pointer and struct types. If
you say that the function takes an int8, Guile will ensure that it can
make an int8; but if you say that the function takes a pointer or a
by-value struct, Guile will only ensure that the arg is a "foreign"
(from foreign.[ch]) pointer, only checking lengths in the case that it's
a struct of known length.

The intention is to provide an expressive Scheme layer, on top of which
any safety constructs can be built as needed.

I would merge it now, except for the fact that it depends on libffi.
Libffi is very portable, and probably exists for all of Guile's
architectures, but it is an extra dependency. Should we require libffi
in Guile 1.9.8? Or should we build the necessary pieces conditionally?

Let me know,


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