gnu: Add ghc-packedstring.

* gnu/packages/haskell.scm (ghc-packedstring): New variable.

gnu/packages/haskell.scm

@@ -5185,6 +5185,35 @@ within an enclosed computation, while remaining responsive to (external)
 asynchronous exceptions.")
     (license expat)))
 
+(define-public ghc-packedstring
+  (package
+    (name "ghc-packedstring")
+    (version "0.1.0.1")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "http://hackage.haskell.org/package/"
+                                  "packedstring/packedstring-"
+                                  version ".tar.gz"))
+              (sha256
+               (base32
+                "1x78pzzdlnpcmh9p37rlf8m5cxf3yqm2alf3whl4zpr9w25r0qj8"))))
+    (build-system haskell-build-system)
+    (arguments
+     `(#:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'enable-extension
+          (lambda _
+            ;; This package won't compile without the StandaloneDeriving
+            ;; extension.
+            (substitute* "packedstring.cabal"
+              (("CPP") "CPP, StandaloneDeriving"))
+            #t)))))
+    (home-page "http://hackage.haskell.org/package/packedstring")
+    (synopsis "Library for packed strings")
+    (description
+     "This deprecated library provides an implementation of packed strings.")
+    (license bsd-3)))
+
 (define-public idris
   (package
     (name "idris")