stack ghci option to switch ghci command and thus use ghci-ng

[rrnewton]

The new stack integration in haskell-mode is great, but the "get type at point" command can't work currently, see: haskell/haskell-mode#889

The problem is it depends on some of the ghci-ng extensions, and there's currently no way to tell stack to use ghci-ng. stack ghci takes an optional --with-ghc option, but that expects a full command-line replacement for ghc, which ghci-ng is not.

What is the right thing here?

[chrisdone]

--with-ghc is the right thing here. It's what you would use with cabal repl --with-ghc to use ghci-ng. It's what I use to use ghci-ng with stack. In my stack projects I have this in my .dir-locals.el:

((haskell-mode
  . ((haskell-process-type . ghci)
     (haskell-process-path-ghci . "stack")
     (haskell-process-args-ghci . ("ghci" "--with-ghc" "ghci-ng")))))

[chrisdone]

Think this can be moved back to the haskell-mode discussion.