Build your Haskell project continuously
TweetToday I am going to introduce handy tools which help you build your Haskell project continuously so that you can see the list of errors and warnings quickly as you program.
Stack
stack build command has --file-watch option. When turned on, stack watches for changes in local files and automatically rebuild.
stack build --file-watchUse --fast option if you want fast build which turns off optimizations (-O0). Also use --pedantic flag if you want to fix all warnings(-Wall and -Werror).
stack build --file-watch --fast --pedanticghcid
Neil Mitchell’s ghcid provides a similar functionality in a different way. It runs GHCi as a daemon and runs :reload whenever your source code changes.
ghcid executes stack ghci by default if you have stack.yaml file and .stack-work directory.
ghcidIf you would like to give a custom command, use --command option.
ghcid "--command=ghci Main.hs"ghcid is much faster than stack build because it uses GHCi.
Steel Overseer
If you want to run arbitrary commands when arbitrary files change, use Steel Overseer instead. You can specify the pattern and commands in .sosrc file using YAML syntax. The following example has two rules.
- Watch
*.hsfiles underSystemdirectory and runstack build. - Watch
*.hsfiles undertestdirectory and runstack test.
- pattern: src/(.*)\.hs
commands:
- stack build
- pattern: test/(.*)\.hs
commands:
- stack testsos command watches the specified files and runs the corresponding commands.
sosWrap-up
These small tools greatly increase your productivity. Please choose one and enjoy instant feedback!