IDE-Haskell-REPL

This package provides a way to interact with ghci (or, alternatively, cabal repl or stack ghci) from Atom.

Repl is opened in the context of the current Atom editor, so there is no need to load the file (even though :l filename will work).

Type any ghci command in the bar at the bottom of the window and press shift+enter (on Win and Linux) or cmd+enter (on macOS) to execute it.

Take a look at ide-haskell-repl.cson for other default bindings.

Four buttons alongside the command bar (outlined green in the picture below) allow for further actions

Action buttons

Left to right:

  • reload file and repeat last command
  • automatic reload file and repeat last command on file save (toggle)
  • interrupt current computation
  • clear window

Repl backend selection

ide-haskell-repl will try to automatically select the correct repl backend (stack/cabal/ghci) based on current builder chosen in ide-haskell-cabal. You can choose none builder to use ghci in plain projects (a.k.a. projects with no *.cabal file).

If ide-haskell-cabal is unavailable (e.g. disabled), ide-haskell-repl will fall back to defaultRepl specified in settings.

Using ide-haskell-repl as IDE backend

ide-haskell-repl can be used to employ GHCi as an IDE backend (in place of ghc-mod etc). At the moment of writing, this mode is somewhat limited, but it does provide types on mouse hover and checking for errors/warnings on save.

To enable, go to ide-haskell-repl settings, and enable “Show Types” and “Check on Save” options: "Show Types" and "Check on Save" checkmarks are enabled

Make sure ide-haskell-repl is the only active backend (that is, disable haskell-ghc-mod package if it’s installed)

Bear in mind that GHCi can be, at times, a memory hog.

Using on Windows

On Windows, interrupting ghci will kill it. There is no good solution to this problem at the moment, but there is a “bad” solution.

Open the command palette (ctrl/cmd+shift+P) and run ide-haskell-repl:setup-ghci-wrapper command. This will download ghci-wrapper.exe, place it into Atom’s user directory, and change ide-haskell-repl configuration to use it.

If you prefer to have more control, you can do the same manually. Get the ghci-wrapper.exe executable from https://github.com/atom-haskell/win-ghci-wrapper/releases (or if you don’t trust random binaries you’ve downloaded from the Internet, you can build it from source – you only really need ghc for that)

Then you need to specify full path to this executable in ghciWrapperPath setting of this package.

For example, if you placed ghci-wrapper.exe in C:\Downloads directory, you need to put C:\Downloads\ghci-wrapper.exe in ghciWrapperPath setting.

Finally, restart any open REPL sessions.

Note that at the time of writing, cabal v2-repl (cabal-install v3.0.0.0) will still die when interrupted. There is no workaround at the moment.

Repl-specific commands

To send command, or move through history, you can use the following commands when focused on repl command editor:

  • ide-haskell-repl:exec-command
  • ide-haskell-repl:history-back
  • ide-haskell-repl:history-forward
  • ide-haskell-repl:ghci-reload

Note that this commands are bound specifically to repl editor, which has CSS selector of atom-text-editor.ide-haskell-repl.

You can rebind those in your keymap, e.g.

"atom-text-editor.ide-haskell-repl":
  'ctrl-enter': 'ide-haskell-repl:exec-command'
  'ctrl-up': 'ide-haskell-repl:history-back'
  'ctrl-down': 'ide-haskell-repl:history-forward'

Just don’t forget to disable default bindings in ide-haskell-repl settings, if you don’t want them.