gnu: Add emacs-agda2-mode

* gnu/packages/agda.scm (emacs-agda2-mode): New variable.

Signed-off-by: Marius Bakke <mbakke@fastmail.com>

gnu/packages/agda.scm

@@ -20,6 +20,7 @@
   #:use-module (gnu packages haskell)
   #:use-module (gnu packages haskell-check)
   #:use-module (gnu packages haskell-web)
+  #:use-module (guix build-system emacs)
   #:use-module (guix build-system haskell)
   #:use-module (guix build-system trivial)
   #:use-module (guix download)
@@ -97,3 +98,19 @@ such as Coq, Epigram and NuPRL.")
     ;; Agda is distributed under the MIT license, and a couple of
     ;; source files are BSD-3.  See LICENSE for details.
     (license (list license:expat license:bsd-3))))
+
+(define-public emacs-agda2-mode
+  (package
+    (inherit agda)
+    (name "emacs-agda2-mode")
+    (build-system emacs-build-system)
+    (inputs '())
+    (arguments
+     `(#:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'enter-elisp-dir
+           (lambda _ (chdir "src/data/emacs-mode") #t)))))
+    (home-page "https://agda.readthedocs.io/en/latest/tools/emacs-mode.html")
+    (synopsis "Emacs mode for Agda")
+    (description "This Emacs mode enables interactive development with
+Agda.  It also aids the input of Unicode characters.")))