tree-sitter-fsharp

tree-sitter grammar for F# (still WIP) Based on the 4.1 F# language specification (Mostly, Appendix A) and the F# compiler parser

Getting started

First, run npm install to install the tree-sitter cli. Next, the grammar can be build using npm run build, or used to parse a file with npm run parse $file

Project structure

The parser consists of two parts:

• src/scanner.cc is responsible for parsing newlines and comments and keeps track of indentation to open and close scopes.
• grammar.js the main tree-sitter grammar. The indent tokens from the external scanner is access though the $.virtual_open_section and virtual_end_section tokens.

The grammar starts with the file node at the begging of the rules.

Adding to neovim

From the local copy:

local parser_config = require "nvim-treesitter.parsers".get_parser_configs()
parser_config.fsharp = {
  install_info = {
    url = "path/to/tree-sitter-fsharp",
    files = {"src/scanner.cc", "src/parser.c" }
  },
  filetype = "fsharp",
}

From GitHub repository:

local parser_config = require "nvim-treesitter.parsers".get_parser_configs()
parser_config.fsharp = {
  install_info = {
    url = "https://github.com/Nsidorenco/tree-sitter-fsharp",
    branch = "develop",
    files = {"src/scanner.cc", "src/parser.c" },
    generate_requires_npm = true,
    requires_generate_from_grammar = true
  },
  filetype = "fsharp",
}

Then run :TSInstallFromGrammar fsharp inside Nvim.

Status

The grammar currently has support for most language features, but might have rough edges. Some parts, like the type annotations are still very bare-bones.

The grammar supports indentation-based scoping but does not fully support offside indentation and opening new indentation levels on record/list construction.

The precedence rules for the different grammar nodes (and particularly expressions) are not set properly yet, which means that the parser size is much larger than needed.

Missing

• Computational expressions
• Type annotations
• Annotations
• Offside tokens inside indentation scope
• Testing
• Set properly precedence rules

Testing

Testing corpus

To run all tests stores in corpus/ run

$ npm test

Test parsing a specific file

$ npm run debug $file

How to contribute

Clone the repo and start playing around with it. If you find a code example which fails to parse, please reduce it to a minimal example, such that it can be added to the corpus as a test case.

PRs fleshing out the grammar or fixing bugs are very welcome!