gnu: Add ghc-cassava-megaparsec.

* gnu/packages/haskell-xyz.scm (ghc-cassava-megaparsec): New variable.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu/packages/haskell-xyz.scm

@@ -1633,6 +1633,37 @@ very simple example of encoding CSV data:
 ")
     (license license:bsd-3)))
 
+(define-public ghc-cassava-megaparsec
+  (package
+    (name "ghc-cassava-megaparsec")
+    (version "2.0.2")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append
+             "https://hackage.haskell.org/package/cassava-megaparsec/"
+             "cassava-megaparsec-"
+             version
+             ".tar.gz"))
+       (sha256
+        (base32
+         "03x1462agrfdagklp8c89b8p4z2hd8nbf6d3895sz770zjkawda7"))))
+    (build-system haskell-build-system)
+    (inputs
+     `(("ghc-cassava" ,ghc-cassava)
+       ("ghc-megaparsec" ,ghc-megaparsec)
+       ("ghc-unordered-containers" ,ghc-unordered-containers)
+       ("ghc-vector" ,ghc-vector)))
+    (native-inputs
+     `(("ghc-hspec" ,ghc-hspec)
+       ("ghc-hspec-megaparsec" ,ghc-hspec-megaparsec)))
+    (home-page "https://github.com/stackbuilders/cassava-megaparsec")
+    (synopsis "Megaparsec parser for CSV files that plays nicely with Cassava")
+    (description
+     "Alternative parser for the Cassava package written with Megaparsec that
+provides for better error messages at the expense of some speed.")
+    (license license:expat)))
+
 (define-public ghc-cborg
   (package
     (name "ghc-cborg")