10 Interactive Haskell

An alternative mode providing a REPL (read–eval–print loop) via GHCi sessions is called haskell-interactive-mode, which effectively replaces inferior-haskell-mode, but comes with a different set of features:

• Separate sessions per Cabal project haskell-session.el.
• A new inferior Haskell process handling code haskell-process.el.
• New REPL implementation similiar to SLIME/IELM
• Navigatable error overlays haskell-interactive-mode.el.

In order to use haskell-interactive-mode instead of the default inferior-haskell-mode, you need to replace some of the default keybindings in the haskell-mode-map keymap with the respective haskell-interactive-mode counterparts:

(eval-after-load "haskell-mode"
  '(progn
    (define-key haskell-mode-map (kbd "C-x C-d") nil)
    (define-key haskell-mode-map (kbd "C-c C-z") 'haskell-interactive-switch)
    (define-key haskell-mode-map (kbd "C-c C-l") 'haskell-process-load-file)
    (define-key haskell-mode-map (kbd "C-c C-b") 'haskell-interactive-switch)
    (define-key haskell-mode-map (kbd "C-c C-t") 'haskell-process-do-type)
    (define-key haskell-mode-map (kbd "C-c C-i") 'haskell-process-do-info)
    (define-key haskell-mode-map (kbd "C-c M-.") nil)
    (define-key haskell-mode-map (kbd "C-c C-d") nil)))

With haskell-interactive-mode, each Haskell source buffer is associated with at most one GHCi session, so when you call haskell-process-load-file for a Haskell source buffer which has no session associated yet, you’re asked which GHCi session to create or associate with.

10.1 Using GHCi-ng

Put :set +c in your .ghci or run it in the REPL. Then use these keybindings:

(define-key interactive-haskell-mode-map (kbd "M-.") 'haskell-mode-goto-loc)
(define-key interactive-haskell-mode-map (kbd "C-c C-t") 'haskell-mode-show-type-at)

You have to load the module before it works, after that it will remember for the current GHCi session.