diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,5 @@
+# Revision history for tree-monad
+
+## 0.3.1 -- 2020-10-23
+
+* Add instances for `MonadFail`
diff --git a/Control/Monad/SearchTree.hs b/Control/Monad/SearchTree.hs
--- a/Control/Monad/SearchTree.hs
+++ b/Control/Monad/SearchTree.hs
@@ -1,28 +1,28 @@
 {-# LANGUAGE Rank2Types #-}
+
 -- |
 -- Module      : Control.Monad.SearchTree
 -- Copyright   : Sebastian Fischer
 -- License     : BSD3
--- 
--- Maintainer  : Sebastian Fischer (sebf@informatik.uni-kiel.de)
+--
+-- Maintainer  : Niels Bunkenburg (nbu@informatik.uni-kiel.de)
 -- Stability   : experimental
 -- Portability : portable
--- 
+--
 -- This Haskell library provides an implementation of the MonadPlus
 -- type class that represents the search space as a tree whose
 -- constructors represent mzero, return, and mplus.
--- 
+--
 -- Such a tree can be used to implement different search strategies,
 -- e.g., by using a queue. It can also be used as a basis for parallel
 -- search strategies that evaluate different parts of the search space
 -- concurrently.
-
 module Control.Monad.SearchTree ( SearchTree(..), Search, searchTree ) where
 
-import Control.Monad
-import Control.Applicative
+import           Control.Applicative
+import           Control.Monad
 
--- | 
+-- |
 -- The type @SearchTree a@ represents non-deterministic computations
 -- as a tree structure.
 data SearchTree a = None | One a | Choice (SearchTree a) (SearchTree a)
@@ -35,34 +35,36 @@
 
 instance Applicative SearchTree where
   pure  = return
+
   (<*>) = ap
 
 instance Alternative SearchTree where
   empty = mzero
+
   (<|>) = mplus
 
 instance Monad SearchTree where
-  return = One
+  return           = One
 
-  None       >>= _ = None
-  One x      >>= f = f x
+  None >>= _       = None
+  One x >>= f      = f x
   Choice s t >>= f = Choice (s >>= f) (t >>= f)
 
+instance MonadFail SearchTree where
   fail _ = None
 
 instance MonadPlus SearchTree where
   mzero = None
+
   mplus = Choice
 
 -- |
 -- Another search monad based on continuations that produce search
 -- trees.
-newtype Search a = Search {
-
-  -- | Passes a continuation to a monadic search action.
-  search :: forall r . (a -> SearchTree r) -> SearchTree r
-
- }
+newtype Search a = Search
+  { -- | Passes a continuation to a monadic search action.
+    search :: forall r. (a -> SearchTree r) -> SearchTree r
+  }
 
 -- | Computes the @SearchTree@ representation of a @Search@ action.
 searchTree :: Search a -> SearchTree a
@@ -73,17 +75,23 @@
 
 instance Applicative Search where
   pure  = return
+
   (<*>) = ap
 
 instance Alternative Search where
   empty = mzero
+
   (<|>) = mplus
 
 instance Monad Search where
-  return x = Search ($x)
-  a >>= f  = Search (\k -> search a (\x -> search (f x) k))
-  fail _   = mzero
+  return x = Search ($ x)
 
+  a >>= f = Search (\k -> search a (\x -> search (f x) k))
+
+instance MonadFail Search where
+  fail _ = mzero
+
 instance MonadPlus Search where
   mzero       = Search (const mzero)
+
   a `mplus` b = Search (\k -> search a k `mplus` search b k)
diff --git a/Setup.hs b/Setup.hs
--- a/Setup.hs
+++ b/Setup.hs
@@ -1,4 +1,2 @@
 import Distribution.Simple
-
 main = defaultMain
-
diff --git a/tree-monad.cabal b/tree-monad.cabal
--- a/tree-monad.cabal
+++ b/tree-monad.cabal
@@ -1,31 +1,29 @@
-Name:          tree-monad
-Version:       0.3
-Cabal-Version: >= 1.6
-Synopsis:      Non-Determinism Monad for Tree Search
-Description:   
-
-  This Haskell library provides an implementation of the MonadPlus
-  type class that represents the search space as a tree whose
-  constructors represent mzero, return, and mplus.
-
-Category:      Control, Monads
-License:       BSD3
-License-File:  LICENSE
-Author:        Sebastian Fischer
-Maintainer:    sebf@informatik.uni-kiel.de
-Bug-Reports:   mailto:sebf@informatik.uni-kiel.de
-Homepage:      http://sebfisch.github.com/tree-monad
-Build-Type:    Simple
-Stability:     experimental
+cabal-version:       >=1.10
 
-Extra-Source-Files: README
+name:                tree-monad
+version:             0.3.1
+synopsis:            Non-Determinism Monad for Tree Search
+description:         This Haskell library provides an implementation of the
+                     MonadPlus type class that represents the search space
+                     as a tree whose constructors represent mzero, return,
+                     and mplus.
+homepage:            http://sebfisch.github.com/tree-monad
+bug-reports:         https://github.com/nbun/tree-monad/issues
+license:             BSD3
+license-file:        LICENSE
+author:              Sebastian Fischer
+maintainer:          nbu@informatik.uni-kiel.de
+category:            Control, Monads
+build-type:          Simple
+extra-source-files:  CHANGELOG.md, README
 
-Library
-  Build-Depends:    base >= 3 && < 5
-  Exposed-Modules:  Control.Monad.SearchTree
-  Ghc-Options:      -Wall
-  Extensions:       Rank2Types
+library
+  exposed-modules:     Control.Monad.SearchTree
+  other-extensions:    Rank2Types
+  build-depends:       base >=4.13 && <4.15
+  default-language:    Haskell2010
+  ghc-options:         -Wall
 
-Source-Repository head
+source-repository head
   type:     git
-  location: git://github.com/sebfisch/tree-monad.git
+  location: git://github.com/nbun/tree-monad.git