From 2ffb8346f135c791c0932e84dcc87a61b3d5481a Mon Sep 17 00:00:00 2001
From: John Soo <address@hidden>
Date: Fri, 13 Dec 2019 09:32:28 -0800
Subject: [PATCH 07/22] gnu: Add ghc-mtl-compat.

* gnu/packages/haskell-xyz.scm (ghc-mtl-compat): New variable.
---
 gnu/packages/haskell-xyz.scm | 39 ++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/gnu/packages/haskell-xyz.scm b/gnu/packages/haskell-xyz.scm
index 64a27e8484..f1c8ae1e89 100644
--- a/gnu/packages/haskell-xyz.scm
+++ b/gnu/packages/haskell-xyz.scm
@@ -7505,6 +7505,45 @@ semi-direct products, \"deletable\" monoids, \"split\" monoids, and
 \"cut\" monoids.")
     (license license:bsd-3)))
 
+(define-public ghc-mtl-compat
+  (package
+    (name "ghc-mtl-compat")
+    (version "0.2.2")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append
+             "mirror://hackage/package/mtl-compat/mtl-compat-"
+             version
+             ".tar.gz"))
+       (sha256
+        (base32
+         "17iszr5yb4f17g8mq6i74hsamii8z6m2qfsmgzs78mhiwa7kjm8r"))))
+    (build-system haskell-build-system)
+    (arguments
+     `(#:tests? #f
+       #:haddock? #f))
+    (home-page
+     "https://github.com/haskell-compat/mtl-compat")
+    (synopsis
+     "Backported Control.Monad.Except module from mtl")
+    (description
+     "This package backports the \"Control.Monad.Except\" module from
+mtl (if using mtl-2.2.0.1 or earlier), which reexports the ExceptT
+monad transformer and the MonadError class.
+
+This package should only be used if there is a need to use the
+Control.Monad.Except module specifically.  If you just want the mtl
+class instances for ExceptT, use transformers-compat instead, since
+mtl-compat does nothing but reexport the instances from that package.
+
+Note that unlike how mtl-2.2 or later works, the
+\"Control.Monad.Except\" module defined in this package exports all of
+ExceptT's monad class instances.  Therefore, you may have to declare
+import Control.Monad.Except () at the top of your file to get all of
+the ExceptT instances in scope.")
+    (license license:bsd-3)))
+
 (define-public ghc-murmur-hash
   (package
     (name "ghc-murmur-hash")
-- 
2.24.0