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G-expression
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Return as a monadic value the absolute file name in the store of the file containing @var{data}, a bytevector. @var{references} is a list of store items that the resulting binary file refers to; it defaults to the empty list.
 
{Monadic Procedure} interned-file @var{file} [@var{name}] @
 
[#:recursive? #t] [#:select? (const #t)] Return the name of @var{file} once interned in the store. Use @var{name} as its store name, or the basename of @var{file} if @var{name} is omitted.
 
When @var{recursive?} is true, the contents of @var{file} are added recursively; if @var{file} designates a flat file and @var{recursive?} is true, its contents are added, and its permission bits are kept.
 
When @var{recursive?} is true, call @code{(@var{select?} @var{file} @var{stat})} for each directory entry, where @var{file} is the entry's absolute file name and @var{stat} is the result of @code{lstat}; exclude entries for which @var{select?} does not return true.
 
The example below adds a file to the store, under two different names:
 
(run-with-store (open-connection)
(mlet %store-monad ((a (interned-file "README"))
(b (interned-file "README" "LEGU-MIN")))
(return (list a b))))

(run-with-store (open-connection)
(mlet %store-monad ((a (interned-file "README"))
(b (interned-file "README" "LEGU-MIN")))
(return (list a b))))

@result{} ("/gnu/store/rwm@dots{}-README" "/gnu/store/44i@dots{}-LEGU-MIN")
 
The @code{(guix packages)} module exports the following package-related monadic procedures:
 
{Monadic Procedure} package-file @var{package} [@var{file}] @
 
[#:system (%current-system)] [#:target #f] @ [#:output "out"] Return as a monadic value in the absolute file name of @var{file} within the @var{output} directory of @var{package}. When @var{file} is omitted, return the name of the @var{output} directory of @var{package}. When @var{target} is true, use it as a cross-compilation target triplet.
 
Note that this procedure does @emph{not} build @var{package}. Thus, the result might or might not designate an existing file. We recommend not using this procedure unless you know what you are doing.
 
{Monadic Procedure} package->derivation @var{package} [@var{system}]
 
{Monadic Procedure} package->cross-derivation @var{package} @
 
@var{target} [@var{system}] Monadic version of @code{package-derivation} and @code{package-cross-derivation} (@pxref{Defining Packages}).
 
G-expression
 
build code quoting
 
So we have ``derivations'', which represent a sequence of build actions to be performed to produce an item in the store (@pxref{Derivations}). These build actions are performed when asking the daemon to actually build the derivations; they are run by the daemon in a container (@pxref{Invoking guix-daemon}).
 
strata of code
 
It should come as no surprise that we like to write these build actions in Scheme. When we do that, we end up with two @dfn{strata} of Scheme code@footnote{The term @dfn{stratum} in this context was coined by Manuel Serrano et al.@: in the context of their work on Hop. Oleg Kiselyov, who has written insightful @url{http://okmij.org/ftp/meta-programming/#meta-scheme, essays and code on this topic}, refers to this kind of code generation as @dfn{staging}.}: the ``host code''---code that defines packages, talks to the daemon, etc.---and the ``build code''---code that actually performs build actions, such as making directories, invoking @command{make}, and so on (@pxref{Build Phases}).
 
To describe a derivation and its build actions, one typically needs to embed build code inside host code. It boils down to manipulating build code as data, and the homoiconicity of Scheme---code has a direct representation as data---comes in handy for that. But we need more than the normal @code{quasiquote} mechanism in Scheme to construct build expressions.
 
The @code{(guix gexp)} module implements @dfn{G-expressions}, a form of S-expressions adapted to build expressions. G-expressions, or @dfn{gexps}, consist essentially of three syntactic forms: @code{gexp}, @code{ungexp}, and @code{ungexp-splicing} (or simply: @code{#~}, @code{#$}, and @code{#$@@}), which are comparable to @code{quasiquote}, @code{unquote}, and @code{unquote-splicing}, respectively (@pxref{Expression Syntax, @code{quasiquote},, guile, GNU Guile Reference Manual}). However, there are major differences:
 
Gexps are meant to be written to a file and run or manipulated by other processes.
 
When a high-level object such as a package or derivation is unquoted inside a gexp, the result is as if its output file name had been introduced.
 
Gexps carry information about the packages or derivations they refer to, and these dependencies are automatically added as inputs to the build processes that use them.
 
lowering, of high-level objects in gexps
 
This mechanism is not limited to package and derivation objects: @dfn{compilers} able to ``lower'' other high-level objects to derivations or files in the store can be defined, such that these objects can also be inserted into gexps. For example, a useful type of high-level objects that can be inserted in a gexp is ``file-like objects'', which make it easy to add files to the store and to refer to them in derivations and such (see @code{local-file} and @code{plain-file} below).
 
To illustrate the idea, here is an example of a gexp:
 
(define build-exp
#~(begin
(mkdir #$output)
(chdir #$output)
(symlink (string-append #$coreutils "/bin/ls")
"list-files")))
(define build-exp
#~(begin
(mkdir #$output)
(chdir #$output)
(symlink (string-append #$coreutils "/bin/ls")
"list-files")))
This gexp can be passed to @code{gexp->derivation}; we obtain a derivation that builds a directory containing exactly one symlink to @file{/gnu/store/@dots{}-coreutils-8.22/bin/ls}:
 
(gexp->derivation "the-thing" build-exp)
 
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G-Expressions

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G-expression
G-выражение
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G-expression
G-выражение
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G-expression
G-Expressions
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G-expression G-выражение guix Glossary

6492436 String information

Source string description
type: cindex
Flags
no-wrap
Source string location
guix-git/doc/guix.texi:12064
String age
4 years ago
Last updated
6 days ago
Source string age
4 years ago
Translation file
po/doc/guix-manual.ru.po, string 4321