Merge pull request #10 from fused-effects/from-readme-to-compileme

Compile the README.

README.lhs

@@ -0,0 +1 @@
+README.md

README.md

@@ -4,16 +4,32 @@
 [![BSD3 license](https://img.shields.io/badge/license-BSD3-blue.svg)](LICENSE)
 [![Build Status](https://action-badges.now.sh/fused-effects/fused-effects-exceptions)](https://github.com/fused-effects/fused-effects-exceptions/actions)
 
+<!--
+Setup, hidden from the rendered markdown.
+
+```haskell
+{-# LANGUAGE ScopedTypeVariables, TypeApplications #-}
+module Main (module Main) where
+
+import Control.Carrier.State.Strict
+import Control.Effect.Exception
+
+main :: IO ()
+main = pure ()
+```
+-->
+
+
 This package provides `Control.Effect.Exception`, a module that wraps the [`Control.Exception`](http://hackage.haskell.org/package/base/docs/Control-Exception.html) API from `base` with the vocabulary provided by the [`fused-effects`](http://hackage.haskell.org/package/fused-effects) library. These functions interact with GHC's support for dynamic exceptions, including functions like `catch` for exception handling and `bracket` for resource management.
 
 Please be aware that injudicious use of these functions may provoke surprising interactions with carriers that thread a monadic state as a parameter, à la the `Control.Carrier.State` types provided by `fused-effects`. For example, a function like `finally`, which does not thread any state from its body to its handler block, may discard state writes in cleanup handlers:
 
 ```haskell
-λ run (runState 'a' ((throwIO (userError "urk") `finally` put @Char 'z')
+discardsState :: IO Char
-    `catch` (\(_ :: IOException) -> pure ())))
+discardsState = execState 'a' ((throwIO (userError "urk") `finally` put @Char 'z')
-('a', ())
+    `catch` (\(_ :: IOException) -> pure ()))
 ```
 
-If this behavior is a concern, a `Control.Carrier.State.IORef` carrier is provided, which fixes this issue given access to a `MonadIO` constraint. If it is not a concern (such as if the cleanup block is only run for its effects in `IO`), then the `StateC` carriers from `fused-effects` will suffice. For more information about the issues associated with this approach, consult Alexis King's excellent [Demystifying `MonadBaseControl`](https://lexi-lambda.github.io/blog/2019/09/07/demystifying-monadbasecontrol/).
+Though the `put @Char 'z'` statement is evaluated, its effect is ultimately discarded; the result of executing the above is `'a'`. If this behavior is a concern, a `Control.Carrier.State.IORef` carrier is provided, which fixes this issue given access to a `MonadIO` constraint. If it is not a concern (such as if the cleanup block is only run for its effects in `IO`), then the `StateC` carriers from `fused-effects` will suffice. For more information about the issues associated with this approach, consult Alexis King's excellent [Demystifying `MonadBaseControl`](https://lexi-lambda.github.io/blog/2019/09/07/demystifying-monadbasecontrol/).
 
 Prior versions of this package provided a `Catch` effect; this has been excised in favor of the more-general `Control.Effect.Exception`, which provides more functionality without requiring any additional carriers beyond a `Lift IO` effect.

fused-effects-exceptions.cabal

@@ -22,9 +22,12 @@ tested-with:
   GHC == 8.6.5
   GHC == 8.8.1
 
-library
+common common
-  hs-source-dirs:      src
   default-language: Haskell2010
+
+library
+  import: common
+  hs-source-dirs: src
   exposed-modules:
     Control.Carrier.State.IORef
     Control.Effect.Exception
@@ -34,8 +37,8 @@ library
     , transformers     >= 0.4 && < 0.6
 
 test-suite test
+  import: common
   type: exitcode-stdio-1.0
-  default-language: Haskell2010
   hs-source-dirs: test
   main-is: Main.hs
   build-depends:
@@ -46,6 +49,18 @@ test-suite test
     , tasty-hunit   ^>= 0.10
     , transformers
 
+test-suite docs
+  import:      common
+  type:        exitcode-stdio-1.0
+  main-is:     README.lhs
+  ghc-options: -pgmL markdown-unlit
+  build-depends:
+      base
+    , fused-effects
+    , fused-effects-exceptions
+  build-tool-depends:
+      markdown-unlit:markdown-unlit ^>= 0.5
+
 source-repository head
   type:     git
   location: https://github.com/fused-effects/fused-effects-exceptions

test/Main.hs

@@ -19,12 +19,12 @@ problematic =
 
 testStateDropsWrites :: Tasty.TestTree
 testStateDropsWrites = HUnit.testCase "State.Strict drops writes" $ do
-  result <- runM . State.execState 'a' $ problematic
+  result <- State.execState 'a' $ problematic
   result HUnit.@?= 'a' -- writes are lost
 
 testIOStatePreservesWrites :: Tasty.TestTree
 testIOStatePreservesWrites = HUnit.testCase "State.IORef preserves writes" $ do
-  result <- runM . IOState.execState 'a' $ problematic
+  result <- IOState.execState 'a' $ problematic
   result HUnit.@?= 'x'
 
 tests :: Tasty.TestTree