hie-core (Haskell IDE engine)

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.

Using it

Install hie-core

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.

Test hie-core

Next, check that hie-core is capable of loading your code. Change to the project directory and run hie-core, which will try and load everything using the same code as the IDE, but in a way that's much easier to understand. For example, taking the example of shake, running hie-core gives some error messages and warnings before reporting at the end:

Files that worked: 152
Files that failed: 6
 * .\model\Main.hs
 * .\model\Model.hs
 * .\model\Test.hs
 * .\model\Util.hs
 * .\output\docs\Main.hs
 * .\output\docs\Part_Architecture_md.hs
Done

Of the 158 files in Shake, as of this moment, 152 can be loaded by the IDE, but 6 can't (error messages for the reasons they can't be loaded are given earlier). The failing files are all prototype work or test output, meaning I can confidently use Shake.

The hie-core executable mostly relies on hie-bios to do the difficult work of setting up your GHC environment. If it doesn't work, see the hie-bios manual to get it working. My default fallback is to figure it out by hand and create a direct style hie.yaml listing the command line arguments to load the project.

Once you have got hie-core working outside the editor, the next step is to pick which editor to integrate with.

Using with VS Code

Install the VS code extension (see https://code.visualstudio.com/docs/setup/mac for details on adding code to your $PATH):

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.

Using with Emacs

If you don't already have MELPA package installation configured, visit MELPA getting started page to get set up. Then, install use-package. Finally, add the following lines to your .emacs.

;; LSP
(use-package flycheck
  :ensure t
  :init
  (global-flycheck-mode t))
(use-package yasnippet
  :ensure t)
(use-package lsp-mode
  :ensure t
  :hook (haskell-mode . lsp)
  :commands lsp)
(use-package lsp-ui
  :ensure t
  :commands lsp-ui-mode)
(use-package lsp-haskell
 :ensure t
 :config
 (setq lsp-haskell-process-path-hie "hie-core")
 (setq lsp-haskell-process-args-hie '())
 ;; Comment/uncomment this line to see interactions between lsp client/server.
 ;;(setq lsp-log-io t)
)