The tooling landscape for text editors has gotten pretty interesting in these years with the advent of VS Code. Yes it is the text editor released by Microsoft and yes it runs on electron. What has it changed in the landscape of tooling for languages you might ask.

Enter Language server protocol.

The Language Server Protocol (LSP) is an open, JSON-RPC-based protocol for use between source code editors or integrated development environments (IDEs) and servers, providing programming language-specific features from the language server to the client. The goal of the protocol is to allow programming language support to be decoupled from any given editor or IDE and even have it distributed over independent language servers.

Again, LSP is an open protocol that can be used by text-editors or IDEs to talk to a process (LSP server) that will provide interactive editing features such as auto-completion, goto function definition, refactorings, documenation etc.

Why should I care?

From the user’s perspective nothing changes. But in terms of tooling for a language this is a big deal. If you want xyz-lang support for Emacs (the interactive editing part), and it doesn’t have it, then you write an new minor-mode for it (think about commint mode). Same goes for Vim and Atom and any other text editor or IDE of your choice. What if you had to write one plugin (or mode in Emacs’s parlance) and it works everywhere… Sounds good right? But still you need a client that speaks LSP on your text editor.

Also remember, using LSP does not make things magically faster or make you architecture superior. It is just a protocol.

Lets talk about Emacs.

Does LSP mean that you can forget about Elisp?

No, You still need Elisp for the LSP-client, configuration, syntax-highlighting, indentation and more.

Again, LSP is for interactive editing features.

So what happens to existing modes such as SLIME, haskell-mode etc?

It is upto the maintainers to bring support for LSP. For SLIME, there is already a Swank server that is used to provide interactive editing features. It might make sense to reimplement it to support LSP (because swank is written in Common Lisp).

If you take a look at the haskell-interactive-mode, it is completely written in Elisp. So lets say haskell-mode speaks LSP but then in order to use it with other text editors you will need Emacs for that plugin to work and you have to install haskell-interactive-mode from MELPA, not many non Emacs users are going to want to use that plugin.

But think about the possibilites, if there were one plugin that works for all text editors (for that language of course), you have a wider audience group and you could potentially get more bug reports, more contributions etc.

There is one more thing, LSP is useful only if a handfull of text editors decide to implement it into themselves. By any means the adoption is going to be a little slow.

One interesting thing that I noticed was that RMS (Richard Stallman) supports LSP and wants it to be a part of Emacs. Here is the email conversation.

What do I have to do with all these?

Surprise, Surprise I got selected for Haskell Summer of Code and I am going to work on haskell-mode, more specifically I’m going to work on haskell-interactive-mode. I’m going to give haskell-interactive-mode a new life of its own (Remove haskell-interactive-mode from haskell-mode and make haskell-interactive-mode a new repository). I’ll also improve the tests suite and implement some new features. Gracjan Polak is my mentor for this HSoC journey. The news has been published on the the HSoC website for quite sometime now, click here to see that.

For me SLIME is the gold standard and I want to imitate it in all ways (for haskell-interactive-mode). I was exploring that for feature parity. My mentor told me about the existence of LSP. Then I took a look at LSP. I thought LSP was awesome. I found that hie (haskell-ide-engine) is already implementing it. That is good; even more good news is that someone is working on improving LSP support for hie via HSoC.

Tooling in the haskell universe for Emacs.

So there is hie. Then I’m working on haskell-interactive-mode. Then there is Intero (this tool provides interactive editing and complements haskell-mode, but you have to use stack to use intero). There are other projects too. This landscape makes me happy because users have choice (This means Haskell is becoming popular in my own metrics).