refers to direct manipulation of C data structures as well as
functions. The traditional &CMUCL; terminology is Alien Interface, and
while that older terminology is no longer used much in the system
-documentation, it still reflected in internal names in the
+documentation, it still reflected in names in the
implementation, notably in the name of the <literal>SB-ALIEN</>
package.</para></note>
<para>
Because of Lisp's emphasis on dynamic memory allocation and garbage
-collection, Lisp implementations use unconventional memory representations
-for objects. This representation mismatch creates problems when a Lisp
-program must share objects with programs written in another language. There
-are three different approaches to establishing communication:
+collection, Lisp implementations use non-C-like memory representations
+for objects. This representation mismatch creates friction when a Lisp
+program must share objects with programs which expect C data. There
+are three common approaches to establishing communication:
<itemizedlist>
<listitem><para>The burden can be placed on the foreign program
(and programmer) by requiring the knowledge and use of the
<para>&SBCL;, like &CMUCL; before it,
relies primarily on the automatic conversion and direct manipulation
-approaches. Aliens of simple scalar types are automatically converted,
-complex types are directly manipulated in their foreign
+approaches. Foreign values of simple scalar types are automatically
+converted, complex types are directly manipulated in their foreign
representation. Furthermore, Lisp strings are represented internally
with null termination bytes so that they can be passed directly to
C interfaces without allocating new zero-terminated copies.</para>
<type>alien-value</> object.</para>
<para>The type language and operations on foreign types are
-intentionally similar to those of the C language. And as discussed
-above, they are applicable not only to communication with native C
-programs, but also to programs in other languages which provide
-C-level interfaces. </para>
+intentionally similar to those of the C language.</para>
</sect1>
<para>Alien types have a description language based on nested list
structure. For example the C type
-<programlisting>
-struct foo {
+<programlisting>struct foo {
int a;
struct foo *b[100];
};</programlisting>
has the corresponding &SBCL; FFI type
-<programlisting>
-(struct foo
+<programlisting>(struct foo
(a int)
(b (array (* (struct foo)) 100)))</programlisting>
</para>
<para>
The foreign types form a subsystem of the &SBCL; type system. An
<type>alien</> type specifier provides a way to use any foreign type as a
-Lisp type specifier. For example
+Lisp type specifier. For example,
<programlisting>(typep foo '(alien (* int)))</programlisting>
can be used to determine whether <varname>foo</> is a pointer to a foreign
<type>int</>. <type>alien</> type specifiers can be used in the same ways
describes a pointer which is represented in Lisp as a
<type>system-area-pointer</> object. &SBCL; exports this type from
<literal>sb-alien</> because &CMUCL; did, but tentatively (as of
- the first draft of this section of the manual, 2002-07-04) it is
+ the first draft of this section of the manual, &SBCL; 0.7.6) it is
deprecated, since it doesn't seem to be required by user code.
</para>
</listitem>
<para>The <function>sb-alien:sap-alien</> function converts <varname>sap</>
(a system area pointer) to a foreign value with the specified
<varname>type</>. <varname>type</> is not evaluated.
-As of 2002-07-04, it looks as though this and other SAP functionality
+As of &SBCL; 0.7.6, it looks as though this and other SAP functionality
may become deprecated, since it shouldn't be needed by user code.
</para>
<para>The <function>sb-alien:alien-sap</> function
returns the SAP which points to <varname>alien-value</>'s data.
-As of 2002-07-04, it looks as though this and other SAP functionality
+As of &SBCL; 0.7.6, it looks as though this and other SAP functionality
may become deprecated, since it shouldn't be needed by user code.
</para>
<para>
Since in modern C libraries, the <varname>errno</> "variable" is typically
-no longer a variable, but some some bizarre artificial construct
+no longer a variable, but some bizarre artificial construct
which behaves superficially like a variable within a given thread,
it can no longer reliably be accessed through the ordinary
<varname>define-alien-variable</> mechanism. Instead, &SBCL; provides
<para>
The <function>extern-alien</> macro
returns an alien with the specified <type>type</> which
-points to an externally defined value. <varname>name</> is not evaluated,
+points to an externally defined value. <varname>name</> is not evaluated,
and may be either a string or a symbol. <type>type</> is
an unevaluated alien type specifier.
</para>
libraries, creating an absolute Unix object file which is then
processed by <function>load-1-foreign</>.</para>
-<para> Note that as of &SBCL; 0.7.5, all foreign code (code loaded
+<note><para>As of &SBCL; 0.7.5, all foreign code (code loaded
with <function>load-1-function</> or <function>load-function</>) is
lost when a Lisp core is saved with
<function>sb-ext:save-lisp-and-die</>, and no attempt is made to
annoyance both for &SBCL; users and for &CMUCL; users.
It's hard to solve this problem completely cleanly, but some
generally-reliable partial solution might be useful. Once someone in
-either camp gets sufficiently annoyed to create it, some mechanism for
-automatically restoring foreign code is likely to be added.</para>
+either camp gets sufficiently annoyed to create it, &SBCL; is
+likely to adopt some mechanism for automatically restoring foreign
+code when a saved core is loaded.</para></note>
</sect1>
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