Removed foreign macros

Converted the function integration to use template
metaprogramming instead of macros.

src/foreign/mod.rs

@@ -5,15 +5,21 @@
 mod atom;
 pub mod cps_box;
 mod extern_fn;
+mod fn_bridge;
 mod inert;
 
 use std::rc::Rc;
 
 pub use atom::{Atom, Atomic, AtomicResult, AtomicReturn};
-pub use extern_fn::{ExternError, ExternFn, XfnResult};
+pub use extern_fn::{ExternError, ExternFn};
+pub use fn_bridge::constructors::{
+  xfn_1ary, xfn_2ary, xfn_3ary, xfn_4ary, xfn_5ary, xfn_6ary, xfn_7ary,
+  xfn_8ary, xfn_9ary,
+};
+pub use fn_bridge::{Param, ToClause};
 pub use inert::InertAtomic;
 
 pub use crate::representations::interpreted::Clause;
 
-/// A type-erased error in external code
-pub type RcError = Rc<dyn ExternError>;
+/// Return type of the argument to the [xfn_1ary] family of functions
+pub type XfnResult<T> = Result<T, Rc<dyn ExternError>>;