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01/03: doc: Explain "file-like objects".
From: |
Ludovic Courtès |
Subject: |
01/03: doc: Explain "file-like objects". |
Date: |
Fri, 05 Jun 2015 20:43:37 +0000 |
civodul pushed a commit to branch master
in repository guix.
commit 343eacbec9d9aa2aed5f9c44b9473cc9dc5e9753
Author: Ludovic Courtès <address@hidden>
Date: Fri Jun 5 14:53:32 2015 +0200
doc: Explain "file-like objects".
* doc/guix.texi (G-Expressions): Mention "file-like objects" and explain
more.
---
doc/guix.texi | 28 +++++++++++++++++++++++-----
1 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/doc/guix.texi b/doc/guix.texi
index 665bdb0..2082fd7 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
address@hidden file-like objects
+The @code{local-file} and @code{plain-file} procedures below return
address@hidden objects}. That is, when unquoted in a G-expression,
+these objects lead to a file in the store. Consider this G-expression:
+
address@hidden
+#~(system* (string-append #$glibc "/sbin/nscd") "-f"
+ #$(local-file "/tmp/my-nscd.conf"))
address@hidden example
+
+The effect here is to ``intern'' @file{/tmp/my-nscd.conf} by copying it
+to the store. Once expanded, for instance @i{via}
address@hidden>derivation}, the G-expression refers to that copy under
address@hidden/gnu/store}; thus, modifying or removing the file in @file{/tmp}
+does not have any effect on what the G-expression does.
address@hidden can be used similarly; it differs in that the file
+content is directly passed as a string.
+
@deffn {Scheme Procedure} local-file @var{file} address@hidden @
[#:recursive? #t]
Return an object representing local file @var{file} to add to the store; this