hie-core (Haskell IDE Core)

Our vision is that you should build an IDE by combining:

• hie-bios for determining where your files are, what are their dependencies, what extensions are enabled and so on;
• hie-core (i.e. this library) for defining how to type check, when to type check, and producing diagnostic messages;
• A bunch of plugins that haven't yet been written, e.g. hie-hlint and hie-ormolu, to choose which features you want;
• haskell-lsp for sending those messages to a Language Server Protocol (LSP) server;
• An extension for your editor. We provide a VS Code extension as extension in this directory, although the components work in other LSP editors too (see below for instructions using Emacs).

There are more details about our approach in this blog post.

How to use it

First install the hie-core binary using stack or cabal, e.g.

1. git clone https://github.com/digital-asset/daml.git
2. cd daml/compiler/hie-core
3. cabal install or stack install (and make sure ~/.local/bin is on your $PATH)

It's important that hie-core is compiled with the same compiler you use to build your projects.

Next, check that hie-bios is able to load your project. This step is currently a bit difficult.

Next, set up an extension for your editor.

Using with VS Code

Install the VS code extension

1. cd compiler/hie-core/extension
2. npm ci
3. npm install vsce --global (may require sudo)
4. vsce package
5. code --install-extension hie-core-0.0.1.vsix

Now openning a .hs file should work with hie-core.

Emacs

The frst step is to install required Emacs packages. If you don't already have Melpa package installation configured in your .emacs, put this stanza at the top.

;;Melpa packages support
(require 'package)
(let* ((no-ssl (and (memq system-type '(windows-nt ms-dos))
                    (not (gnutls-available-p))))
       (proto (if no-ssl "http" "https")))
  (when no-ssl
    (warn "\
Your version of Emacs does not support SSL connections,
which is unsafe because it allows man-in-the-middle attacks.
There are two things you can do about this warning:
1. Install an Emacs version that does support SSL and be safe.
2. Remove this warning from your init file so you won't see it again."))
  ;; Comment/uncomment these two lines to enable/disable MELPA and MELPA Stable as desired
  (add-to-list 'package-archives (cons "melpa" (concat proto "://melpa.org/packages/")) t)
  ;;(add-to-list 'package-archives (cons "melpa-stable" (concat proto "://stable.melpa.org/packages/")) t)
  (when (< emacs-major-version 24)
    ;; For important compatibility libraries like cl-lib
    (add-to-list 'package-archives (cons "gnu" (concat proto "://elpa.gnu.org/packages/")))))
(package-initialize)
;; Remember : to avoid package-not-found errors, refresh the package
;; database now and then with M-x package-refresh-contents.

When this is in your .emacs and evaluated, M-x package-refresh-contents to get the package database downloaded and then M-x package-list-packages to display the available packages. Click on a package to install it. You'll need to install the following packages:

• lsp-haskell
• lsp-ui
• flycheck
• yasnippet

When done with this, add the following lines to your .emacs:

;; LSP support for Haskell
(require 'lsp)
(require 'lsp-haskell)
(require 'yasnippet)
(add-hook 'haskell-mode-hook #'lsp)
(setq lsp-haskell-process-path-hie "hie-core")
(setq lsp-haskell-process-args-hie '())

Optionally, you may wish to add the following conveniences:

;; Enable LSP logging (helpful for debugging)
(setq lsp-log-io t)

;; Keyboard mappings for goto next/previous error
(define-key flymake-mode-map (kbd "M-n") 'flymake-goto-next-error)
(define-key flymake-mode-map (kbd "M-p") 'flymake-goto-prev-error)

Testing

For testing, I've been using the ghc-lib-gen target of the ghc-lib project. Navigate to the root of ghc-lib and create an hie.yaml file with contents

cradle: {cabal: {component: "exe:ghc-lib-gen"}}

Invoke cabal new-configure -w ~/.stack/programs/~/.stack/programs/x86_64-osx/ghc-8.6.5/bin/ghc (this is the ghc used by stack to build hie-core - consult //compiler/hie-core/stack.yaml to help work out what you should write here). This last step will create a file cabal.project.local with contents pointing cabal to use the desired ghc. You can build ghc-lib-gen from the ghc-lib directory with the command cabal new-build as you like. After creating cabal.project.local, you should be all set. Open ghc-lib/ghc-lib-gen/src/Main.hs in a buffer and, for example, hover should bring up type/definition info.