Import improvements from MTL 2.2 and 2.3

.git-blame-ignore-revs

@@ -0,0 +1,2 @@
+# Ormolu formatting
+e8d793c8fabcb9b40429c538a42aee103d2d9d05

.github/workflows/ci.yml

@@ -0,0 +1,42 @@
+name: CI
+
+# Trigger the workflow on push or pull request, but only for the main branch
+on:
+  pull_request:
+  push:
+    branches: ["master"]
+
+jobs:
+  ormolu:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: haskell-actions/run-ormolu@v15
+  native:
+    name: "Native: GHC ${{ matrix.ghc }} on ${{ matrix.os }}"
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        ghc: ['9.2', '9.4', '9.6', '9.8']
+    steps:
+      - name: Checkout base repo
+        uses: actions/checkout@v4
+      - name: Set up Haskell
+        id: setup-haskell
+        uses: haskell-actions/setup@v2
+        with:
+          ghc-version: ${{ matrix.ghc }}
+          cabal-version: 'latest'
+      - name: Configure
+        run: cabal new-configure
+      - name: Freeze
+        run: cabal freeze
+      - name: Cache
+        uses: actions/cache@v3
+        with:
+          path: ${{ steps.setup-haskell.outputs.cabal-store }}
+          key: ${{ runner.os }}-${{ matrix.ghc }}-${{ hashFiles('cabal.project.freeze') }}
+          restore-keys: ${{ runner.os }}-${{ matrix.ghc }}-
+      - name: Build
+        run: cabal build all

.gitignore

@@ -0,0 +1 @@
+dist-newstyle

demo/demo.cabal

@@ -7,7 +7,7 @@ common base
   default-language: GHC2021
   ghc-options: -Wall
   build-depends:
-    , base ^>= 4.16 || ^>= 4.17 || ^>= 4.18
+    , base ^>= 4.16 || ^>= 4.17 || ^>= 4.18 || ^>= 4.19
     , monads-tf
   default-extensions:
     TypeFamilies

demo/except-1/Main.hs

@@ -1,16 +1,17 @@
 import Control.Monad.Except
 
 -- This is the type to represent length calculation error.
-data LengthError = EmptyString  -- Entered string was empty.
-          | StringTooLong Int   -- A string is longer than 5 characters.
-                                -- Records a length of the string.
-          | OtherError String   -- Other error, stores the problem description.
+data LengthError
+  = EmptyString -- Entered string was empty.
+  | StringTooLong Int -- A string is longer than 5 characters.
+  -- Records a length of the string.
+  | OtherError String -- Other error, stores the problem description.
 
 -- Converts LengthError to a readable message.
 instance Show LengthError where
   show EmptyString = "The string was empty!"
   show (StringTooLong len) =
-      "The length of the string (" ++ (show len) ++ ") is bigger than 5!"
+    "The length of the string (" ++ (show len) ++ ") is bigger than 5!"
   show (OtherError msg) = msg
 
 -- For our monad type constructor, we use Either LengthError
@@ -29,9 +30,11 @@ main = do
 -- The processing is done in Either monad.
 calculateLengthOrFail :: String -> LengthMonad Int
 calculateLengthOrFail [] = throwError EmptyString
-calculateLengthOrFail s | len > 5 = throwError (StringTooLong len)
-                        | otherwise = return len
-  where len = length s
+calculateLengthOrFail s
+  | len > 5 = throwError (StringTooLong len)
+  | otherwise = return len
+  where
+    len = length s
 
 -- Prints result of the string length calculation.
 reportResult :: LengthMonad Int -> IO ()

demo/except-2/Main.hs

@@ -1,4 +1,5 @@
 import Control.Monad.Except
+import Control.Monad.IO.Class
 
 -- An IO monad which can return String failure.
 -- It is convenient to define the monad type of the combined monad,

flake.nix

@@ -1,6 +1,6 @@
 {
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.11";
     flake-utils.url = "github:numtide/flake-utils";
   };