add ormolu formatter

.pre-commit-config.yaml

@@ -0,0 +1,16 @@
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.3.0
+    hooks:
+      - id: check-yaml
+      - id: end-of-file-fixer
+      - id: trailing-whitespace
+  - repo: local
+    hooks:
+      - id: ormolu-formatter
+        name: ormolu-formatter
+        entry: bash -c "stack install ormolu && ormolu --mode inplace $(find . -name '*.hs')"
+        language: system
+        types: [haskell]
+        pass_filenames: false
+        always_run: true

Dockerfile

@@ -10,9 +10,17 @@ RUN curl -sSL https://get.haskellstack.org/ | sh
 ENV PATH="/root/.local/bin:${PATH}"
 RUN stack --resolver ghc-9.6.4 setup
 
+RUN stack install omolu
+
 WORKDIR /peter-lang
 
 COPY . /peter-lang
 
-RUN stack build 
+# cancel the build if there are formatting errors
+RUN ormolu --mode check $(find . -name '*.hs')
+# build project
+RUN stack build
 RUN stack test
+# pre-commit
+RUN git init . && pre-commit install-hooks
+RUN pre-commit run --all-files

Setup.hs

@@ -1,2 +1,3 @@
 import Distribution.Simple
+
 main = defaultMain

src/Lib.hs

@@ -1,6 +1,7 @@
 module Lib
-    ( someFunc
-    ) where
+  ( someFunc,
+  )
+where
 
 someFunc :: IO ()
 someFunc = putStrLn "someFunc"