From 48566e3dd705cbd2f8ad34b38e03e639e9e6e5a7 Mon Sep 17 00:00:00 2001
From: Alex Vong <alexvong1995@gmail.com>
Date: Sun, 6 Aug 2017 23:39:55 +0800
Subject: [PATCH 3/6] gnu: Add ghc-stmonadtrans.

* gnu/packages/haskell.scm (ghc-stmonadtrans): New variable.
---
 gnu/packages/haskell.scm | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/gnu/packages/haskell.scm b/gnu/packages/haskell.scm
index d0e6a64ce..44797a226 100644
--- a/gnu/packages/haskell.scm
+++ b/gnu/packages/haskell.scm
@@ -7076,6 +7076,31 @@ other transformers.")
                (base32
                 "0a364zfcm17mhpy0c4ms2j88sys4yvgd6071qsgk93la2wjm8mkr"))))))
 
+(define-public ghc-stmonadtrans
+  (package
+    (name "ghc-stmonadtrans")
+    (version "0.4.3")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append "https://hackage.haskell.org/package/STMonadTrans"
+                           "/STMonadTrans-" version ".tar.gz"))
+       (sha256
+        (base32 "1nr26fnmi5fdjc6d00w13kjhmfyvb5b837d0006w4dj0yxndaksp"))))
+    (build-system haskell-build-system)
+    (inputs
+     `(("ghc-mtl" ,ghc-mtl)))
+    (home-page "https://hackage.haskell.org/package/STMonadTrans")
+    (synopsis "Monad transformer version of the ST monad")
+    (description
+     "A monad transformer version of the ST monad Warning! This monad
+transformer should not be used with monads that can contain multiple answers,
+like the list monad.  The reason is that the state token will be duplicated
+across the different answers and this causes Bad Things to happen (such as loss
+of referential transparency).  Safe monads include the monads State, Reader,
+Writer, Maybe and combinations of their corresponding monad transformers.")
+    (license license:bsd-3)))
+
 (define-public ghc-findbin
   (package
     (name "ghc-findbin")
-- 
2.13.4