diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,4 +1,5 @@
 # hw-string-parse
-[![CircleCI](https://circleci.com/gh/haskell-works/hw-string-parse/tree/0-branch.svg?style=svg)](https://circleci.com/gh/haskell-works/hw-string-parse/tree/0-branch)
+
+[![CircleCI](https://circleci.com/gh/haskell-works/hw-string-parse.svg?style=svg)](https://circleci.com/gh/haskell-works/hw-string-parse)
 
 Simple parser combinator library for strings.
diff --git a/doctest/DoctestDriver.hs b/doctest/DoctestDriver.hs
new file mode 100644
--- /dev/null
+++ b/doctest/DoctestDriver.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE CPP #-}
+
+#if MIN_VERSION_GLASGOW_HASKELL(8,4,4,0)
+{-# OPTIONS_GHC -F -pgmF doctest-discover #-}
+#else
+module Main where
+
+import qualified System.IO as IO
+
+main :: IO ()
+main = IO.putStrLn "WARNING: doctest will not run on GHC versions earlier than 8.4.4"
+#endif
diff --git a/hw-string-parse.cabal b/hw-string-parse.cabal
--- a/hw-string-parse.cabal
+++ b/hw-string-parse.cabal
@@ -1,41 +1,69 @@
+cabal-version: 2.2
+
 name:                   hw-string-parse
-version:                0.0.0.4
+version:                0.0.0.5
 synopsis:               String parser
 description:            Please see README.md
+category:               Data, Bit
+stability:              Experimental
 homepage:               http://github.com/haskell-works/hw-string-parse#readme
-license:                BSD3
-license-file:           LICENSE
+bug-reports:            https://github.com/haskell-works/hw-string-parse/issues
 author:                 John Ky
 maintainer:             newhoggy@gmail.com
-copyright:              2016 John Ky
-category:               Data, Bit
-stability:              Experimental
+copyright:              2016-2021 John Ky
+license:                BSD-3-Clause
+license-file:           LICENSE
+tested-with:            GHC == 9.2.2, GHC == 9.0.2, GHC == 8.10.7, GHC == 8.8.4, GHC == 8.6.5
 build-type:             Simple
 extra-source-files:     README.md
-cabal-version:          >= 1.22
 
-library
-  hs-source-dirs:       src
-  exposed-modules:      HaskellWorks.Data.String.Parse
-  build-depends:        base                          >= 4          && < 5
+source-repository head
+  type: git
+  location: https://github.com/haskell-works/hw-string-parse
 
+common base                       { build-depends: base                       >= 4.11       && < 5      }
+
+common doctest                    { build-depends: doctest                    >= 0.16.2     && < 0.21   }
+common doctest-discover           { build-depends: doctest-discover           >= 0.2        && < 0.3    }
+common QuickCheck                 { build-depends: QuickCheck                                           }
+common bytestring                 { build-depends: bytestring                                           }
+common hspec                      { build-depends: hspec                                                }
+common vector                     { build-depends: vector                                               }
+
+common config
   default-language:     Haskell2010
+
+common hw-string-parse
+  build-depends:        hw-string-parse
+
+library
+  import:               base, config
+  exposed-modules:      HaskellWorks.Data.String.Parse
+  other-modules:        Paths_hw_string_parse
+  autogen-modules:      Paths_hw_string_parse
+  hs-source-dirs:       src
   ghc-options:          -Wall -O2 -msse4.2
 
 test-suite hw-string-parse-test
-  type:                 exitcode-stdio-1.0
-  hs-source-dirs:       test
-  main-is:              Spec.hs
-  other-modules:
-  build-depends:        base                          >= 4          && < 5
+  import:               base, config
+                      , QuickCheck
                       , bytestring
                       , hspec
-                      , hw-string-parse
-                      , QuickCheck
                       , vector
-  ghc-options:          -threaded -rtsopts -with-rtsopts=-N -Wall
-  default-language:     Haskell2010
+  type:                 exitcode-stdio-1.0
+  main-is:              Spec.hs
+  hs-source-dirs:       test
+  ghc-options:          -Wall -threaded -rtsopts -with-rtsopts=-N
+  build-tool-depends:   hspec-discover:hspec-discover
+  build-depends:        hw-string-parse
 
-source-repository head
-  type:     git
-  location: https://github.com/haskell-works/hw-string-parse
+test-suite doctest
+  import:               base, config
+                      , doctest
+                      , doctest-discover
+                      , hw-string-parse
+  type:                 exitcode-stdio-1.0
+  ghc-options:          -threaded -rtsopts -with-rtsopts=-N
+  main-is:              DoctestDriver.hs
+  HS-Source-Dirs:       doctest
+  build-tool-depends:   doctest-discover:doctest-discover
diff --git a/src/HaskellWorks/Data/String/Parse.hs b/src/HaskellWorks/Data/String/Parse.hs
--- a/src/HaskellWorks/Data/String/Parse.hs
+++ b/src/HaskellWorks/Data/String/Parse.hs
@@ -28,11 +28,10 @@
   fmap f (Parser cs) = Parser (\s -> [(f a, b) | (a, b) <- cs s])
 
 instance Applicative Parser where
-  pure = return
+  pure = unit
   (Parser cs1) <*> (Parser cs2) = Parser (\s -> [(f a, s2) | (f, s1) <- cs1 s, (a, s2) <- cs2 s1])
 
 instance Monad Parser where
-  return = unit
   (>>=)  = bind
 
 instance MonadPlus Parser where