gnu: Add scsh.

* gnu/packages/shells.scm (scsh): New variable.

gnu/packages/shells.scm

@@ -37,6 +37,7 @@ (define-module (gnu packages shells)
   #:use-module (gnu packages pkg-config)
   #:use-module (gnu packages python)
   #:use-module (gnu packages readline)
+  #:use-module (gnu packages scheme)
   #:use-module (guix build-system gnu)
   #:use-module (guix build-system python)
   #:use-module (guix download)
@@ -382,3 +383,51 @@ (define-public xonsh
 systems including Linux, Mac OSX, and Windows.  Xonsh is meant for the daily
 use of experts and novices alike.")
     (license bsd-2)))
+
+(define-public scsh
+  (let ((commit "114432435e4eadd54334df6b37fcae505079b49f")
+        (revision "1"))
+    (package
+      (name "scsh")
+      (version (string-append "0.0.0-" revision "." (string-take commit 7)))
+      (source
+       (origin
+         (method git-fetch)
+         (uri (git-reference
+               (url "https://github.com/scheme/scsh")
+               (commit commit)))
+         (file-name (string-append name "-" version "-checkout"))
+         (sha256
+          (base32
+           "1ghk08akiz7hff1pndi8rmgamgcrn2mv9asbss9l79d3c2iaav3q"))))
+      (build-system gnu-build-system)
+      (arguments
+       `(#:test-target "test"
+         #:phases
+         (modify-phases %standard-phases
+           (add-before 'configure 'replace-rx
+             (lambda* (#:key inputs #:allow-other-keys)
+               (let* ((rx (assoc-ref inputs "scheme48-rx"))
+                      (rxpath (string-append rx "/share/scheme48-"
+                                             ,(package-version scheme48)
+                                             "/rx")))
+                 (delete-file-recursively "rx")
+                 (symlink rxpath "rx"))
+               #t))
+           (add-before 'configure 'autoreconf
+             (lambda _
+               (zero? (system* "autoreconf")))))))
+      (inputs
+       `(("scheme48" ,scheme48)
+         ("scheme48-rx" ,scheme48-rx)))
+      (native-inputs
+       `(("autoconf" ,autoconf)
+         ("automake" ,automake)))
+      (home-page "https://github.com/scheme/scsh")
+      (synopsis "Unix shell embedded in Scheme")
+      (description
+       "Scsh is a Unix shell embedded in Scheme.  Scsh has two main
+components: a process notation for running programs and setting up pipelines
+and redirections, and a complete syscall library for low-level access to the
+operating system.")
+      (license bsd-3))))