Add proposal for LSP support in jupyterlab-monaco

jupyterlab-monaco-lsp/jupyterlab-monaco-lsp.md

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+# Langage server protocol (LSP) support in jupyterlab-monaco
+
+## Problem
+
+The [monaco-editor](https://github.com/Microsoft/monaco-editor) is an
+open-source text editor written in Javascript and used in [VS
+Code](https://code.visualstudio.com/).
+
+[jupyterlab-monaco](https://github.com/jupyterlab/jupyterlab-monaco) is a JupyterLab
+extension that allows users to edit documents using monaco-editor.
+
+monaco-editor ships with language features for
+TypeScript, JavaScript, CSS, LESS, SCSS, JSON, HTML. In order to support other
+languages (e.g. Python), it must connect to a language server (e.g. Python language
+server).
+
+## Proposed Enhancement
+
+- Create a notebook server extension to allow clients to connect with language servers
+  - Provide HTTP interface for clients to communicate via websockets
+    - e.g. `/lsp/python/` or `/lsp/r/`.
+  - Add a new set of classes to
+    [@jupyterlab/services](https://github.com/jupyterlab/jupyterlab/tree/master/packages/services)
+    that provide a client-side interface to those endpoints
+- Integrate monaco-editor in jupyterlab-monaco with classes in @jupyterlab/services
+
+## Notes
+
+### Libraries
+
+- [monaco-languageclient](https://github.com/TypeFox/monaco-languageclient):
+  NPM module to connect Monaco editor with language servers
+
+### Reference implementations
+
+- [WIP] changes to import monaco-lsp code into jupyterlab-monaco ([jupyterlab-monaco#12](https://github.com/jupyterlab/jupyterlab-monaco/pull/12))
+- [Theia](https://github.com/theia-ide/theia)
+- [Gitpod](https://github.com/gitpod-io/gitpod)
+- [R-Brain](https://github.com/R-Brain/jupyterlab/blob/master/packages/monaco-extension/src/index.ts)
+
+### Documentation
+
+- [Language servers](https://langserver.org/#implementations-server)