gnu: Add ghc-prettyclass.

* gnu/package/haskell-xyz.scm: New file.
* gnu/local.mk: Add it.
* gnu/packages/haskell-xyz.scm (ghc-prettyclass): New variable.

gnu/local.mk

@@ -238,6 +238,7 @@ GNU_SYSTEM_MODULES =				\
   %D%/packages/haskell-check.scm		\
   %D%/packages/haskell-crypto.scm		\
   %D%/packages/haskell-web.scm			\
+  %D%/packages/haskell-xyz.scm			\
   %D%/packages/ham-radio.scm			\
   %D%/packages/hexedit.scm			\
   %D%/packages/hugs.scm				\

gnu/packages/haskell-xyz.scm

@@ -0,0 +1,45 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Robert Vollmert <rob@vllmrt.net>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu packages haskell-xyz)
+  #:use-module (gnu packages)
+  #:use-module (guix build-system haskell)
+  #:use-module (guix download)
+  #:use-module ((guix licenses) #:prefix license:)
+  #:use-module (guix packages))
+
+(define-public ghc-prettyclass
+  (package
+    (name "ghc-prettyclass")
+    (version "1.0.0.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append "https://hackage.haskell.org/package/"
+                           "prettyclass/prettyclass-" version ".tar.gz"))
+       (sha256
+        (base32
+         "11l9ajci7nh1r547hx8hgxrhq8mh5gdq30pdf845wvilg9p48dz5"))))
+    (build-system haskell-build-system)
+    (home-page "http://hackage.haskell.org/package/prettyclass")
+    (synopsis "Pretty printing class similar to Show")
+    (description "This package provides a pretty printing class similar
+to @code{Show}, based on the HughesPJ pretty printing library.  It
+provides the pretty printing class and instances for the Prelude
+types.")
+    (license license:bsd-3)))