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authorLudovic Courtès <ludo@gnu.org>2015-06-05 14:53:32 +0200
committerLudovic Courtès <ludo@gnu.org>2015-06-05 15:25:08 +0200
commit343eacbec9d9aa2aed5f9c44b9473cc9dc5e9753 (patch)
treeffd390a6e8cea7830965f312453a7a3c066ded1f
parent97cc51f87605ca78af3b8c2e8094b6f244fbb11a (diff)
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doc: Explain "file-like objects".
* doc/guix.texi (G-Expressions): Mention "file-like objects" and explain more.
-rw-r--r--doc/guix.texi28
1 files changed, 23 insertions, 5 deletions
diff --git a/doc/guix.texi b/doc/guix.texi
index 665bdb028d..2082fd765c 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -2942,12 +2942,12 @@ and these dependencies are automatically added as inputs to the build
processes that use them.
@end itemize
-Actually this mechanism is not limited to package and derivation
-objects; @dfn{compilers} able to ``lower'' other high-level objects to
+This mechanism is not limited to package and derivation
+objects: @dfn{compilers} able to ``lower'' other high-level objects to
derivations can be defined, such that these objects can also be inserted
-into gexps. Another useful type of high-level object that can be
-inserted in a gexp is @dfn{local files}, which allows files from the
-local file system to be added to the store and referred to by
+into gexps. For example, a useful type of high-level object that can be
+inserted in a gexp is ``file-like objects'', which make it easy to
+add files to the store and refer to them in
derivations and such (see @code{local-file} and @code{plain-file}
below.)
@@ -3113,6 +3113,24 @@ refer to. Any reference to another store item will lead to a build error.
The other arguments are as for @code{derivation} (@pxref{Derivations}).
@end deffn
+@cindex file-like objects
+The @code{local-file} and @code{plain-file} procedures below return
+@dfn{file-like objects}. That is, when unquoted in a G-expression,
+these objects lead to a file in the store. Consider this G-expression:
+
+@example
+#~(system* (string-append #$glibc "/sbin/nscd") "-f"
+ #$(local-file "/tmp/my-nscd.conf"))
+@end example
+
+The effect here is to ``intern'' @file{/tmp/my-nscd.conf} by copying it
+to the store. Once expanded, for instance @i{via}
+@code{gexp->derivation}, the G-expression refers to that copy under
+@file{/gnu/store}; thus, modifying or removing the file in @file{/tmp}
+does not have any effect on what the G-expression does.
+@code{plain-file} can be used similarly; it differs in that the file
+content is directly passed as a string.
+
@deffn {Scheme Procedure} local-file @var{file} [@var{name}] @
[#:recursive? #t]
Return an object representing local file @var{file} to add to the store; this