guix repl command gives you access to a warm and friendly
read-eval-print loop (REPL) (see Invoking guix repl). If
you’re getting into Guix programming—defining your own packages,
writing manifests, defining services for Guix System or Guix Home,
etc.—you will surely find it convenient to toy with ideas at the REPL.
If you use Emacs, the most convenient way to do that is with Geiser
(see The Perfect Setup), but you do not have to use Emacs to enjoy
the REPL. When using
guix repl or
guile in the
terminal, we recommend using Readline for completion and Colorized to
get colorful output. To do that, you can run:
guix install guile guile-readline guile-colorized
... and then create a .guile file in your home directory containing this:
The REPL lets you evaluate Scheme code; you type a Scheme expression at the prompt, and the REPL prints what it evaluates to:
$ guix repl scheme@(guix-user)> (+ 2 3) $1 = 5 scheme@(guix-user)> (string-append "a" "b") $2 = "ab"
It becomes interesting when you start fiddling with Guix at the REPL.
The first thing you’ll want to do is to “import” the
module, which gives access to the main part of the programming
interface, and perhaps a bunch of useful Guix modules. You could type
(use-modules (guix)), which is valid Scheme code to import a
module (see Using Guile Modules in GNU Guile Reference
Manual), but the REPL provides the
use command as a
shorthand notation (see REPL Commands in GNU Guile Reference
scheme@(guix-user)> ,use (guix) scheme@(guix-user)> ,use (gnu packages base)
Notice that REPL commands are introduced by a leading comma. A REPL
use is not valid Scheme code; it’s interpreted
specially by the REPL.
Guix extends the Guile REPL with additional commands for convenience.
Among those, the
build command comes in handy: it ensures that
the given file-like object is built, building it if needed, and returns
its output file name(s). In the example below, we build the
grep packages, as well as a “computed
computed-file), and we use the
scandir procedure to list the files in Grep’s
scheme@(guix-user)> ,build coreutils $1 = "/gnu/store/…-coreutils-8.32-debug" $2 = "/gnu/store/…-coreutils-8.32" scheme@(guix-user)> ,build grep $3 = "/gnu/store/…-grep-3.6" scheme@(guix-user)> ,build (computed-file "x" #~(mkdir #$output)) building /gnu/store/…-x.drv... $4 = "/gnu/store/…-x" scheme@(guix-user)> ,use(ice-9 ftw) scheme@(guix-user)> (scandir (string-append $3 "/bin")) $5 = ("." ".." "egrep" "fgrep" "grep")
At a lower-level, a useful command is
lower: it takes a file-like
object and “lowers” it into a derivation (see Derivations) or a
scheme@(guix-user)> ,lower grep $6 = #<derivation /gnu/store/…-grep-3.6.drv => /gnu/store/…-grep-3.6 7f0e639115f0> scheme@(guix-user)> ,lower (plain-file "x" "Hello!") $7 = "/gnu/store/…-x"
The full list of REPL commands can be seen by typing
and is given below for reference.
Lower object and build it if it’s not already built, returning its output file name(s).
Lower object into a derivation or store file name and return it.
Change build verbosity to level.
This is similar to the --verbosity command-line option (see Common Build Options): level 0 means total silence, level 1 shows build events only, and higher levels print build logs.
Run exp, a monadic expresssion, through the store monad. See The Store Monad, for more information.
Enter a new REPL to evaluate monadic expressions (see The Store Monad). You can quit this “inner” REPL by typing