fennel-nvim

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running fennel-lang natively in neovim

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# fennel-nvim [WIP]

**Experimental** plugin adding native [fennel](https://fennel-lang.org) support to nvim by utilizing neovim's native Lua support. No RPC necessary!

I will likely extend this in the future, but for now I'm just testing out the idea. It should be possible reach seamless integration with a little extra work.

Currently bundled with Fennel `0.4.0-dev`, from the current master branch as of
[this commit](https://github.com/bakpakin/Fennel/tree/d3620b369a6d16f55f98d939a3b47b56d97b9f19).

This is basically just `0.3.0` with an extra docstring or two and better readline completion from the repl
(which requires `readline.lua` to be installed and present on package.path).
In the future, I will switch this over to only bundling a full release, and allowing an option to easily supply a custom version.

- [Install](#install)
- [Fennel Environment](#fennel-environment)
- [Usage](#usage)
  - [init.fnl](#initfnl)
  - [Commands](#commands)
- [Neovim Lua Completion](#completion)
- [Configuration](#configuration)

## Install

The usual, either clone this repository to the plugin directory (or in nvim, somewhere on your `runtimepath`) or a plugin manager of your choice.

```viml
Plug 'jaawerth/fennel-nvim' " using vim-plug
```

## Fennel Environment

This plugin runs your Fennel code under a custom environment which you can alter by passing, as a second argument
to the functions below, an `env` table. It inherits from nvim's `_G`, so you will have access to all normal globals,
including neovim's Lua API.

In addition to the above, for convenient it exposes the `fennelview` function/module as `view` for easy access.

## Usage

The following allows you to run fennel code via Lua in neovim.
For the Lua API to manipulate neovim from Lua/Fennel, see `:help lua-vim`, `:help lua`, and `:help api`.

### `init.fnl`

See `:help init.fnl`. This plugin, when installed on your `runtimepath`, will automatically look for an `init.fnl` file in your
neovim configuration directories (see `:help xdg` and `:help stdpath`). On Linux, this defaults to `$HOME/.config/nvim/`.

You can disable this behavior as follows in your `init.vim`:

```viml
let g:fennel_nvim_auto_init = v:false
```

### Commands

#### Eval some Fennel: `Fnl`

```viml
:Fnl (doc doc)
" Output:
" (doc x)
"   Print the docstring and arglist for a function, macro, or special form.
```

**Note:** Unlike `:lua`, this will not work with heredoc (`<<`) syntax, as that is only available
to built-in commands. This behavior may become available in the future when neovim implements `:here`
(per [this issue](https://github.com/neovim/neovim/issues/7638)).

Using the `fnl#eval(code[, arg][, compileOpts])` function - like `luaeval()`, you can pass an argument,
which will be bound to the magic global `_A` in the running environment.

```viml
:call fnl#eval('(print (.. "Hello, " _A "!"))', 'World')
" outputs: Hello, World!
```

#### Run a file: `FnlFile`

With `:FnlFile path/to/file.fnl` or simply use `FnlFile` to source `.fnl` files from `init.vim`

For example, if editing some fennel code you want to test in neovim itself,
```viml
:FnlFile %
```

Similarly, you can use `fnl#eval(filepath[, compileOpts])`.

#### Execute Fennel on a range of lines: `FnlDo`

Fennel analog to `luado` (see `:help luado`). Select/enter a range of lines (defaults to every line in the buffer)
and the expressions you give it will be wrapped in a function, which is executed for every line, with `line, linenr` passed
as named arguments.

```viml
" print first 5 lines preceded by line #
:1,5FnlDo (print linenr line)
" print the width of every line in file
:FnlDo (print (string.format "line %d is %d chars wide" linenr (# line)))
```
Can be invoked as a range function with `<range>call fnl#do(exprStr)` (see `:help call`).

Also available from Lua: `require('fennel-nvim').dolines(exprStr, firstline, lastline)`

## Completion
For convenience, this module comes with a couple of functions that can be used with `omnifunc`. See `:help fennel-completion`.
Note that this will only complete on globals and specials/macros currently, using Neovim's internal Lua/Fennel environment.

## Configuration

### `g:fennel_nvim_auto_init`

See `:help g:fennel_nvim_auto_init` for disabling auto-source of `init.fnl`

### Disable automatic patching of package.loaders

To make `require` correctly find Fennel modules using `fennel.path`, `package.loaders` (or `package.searchers` in Lua 5.3 environments)
is patched to include `fennel.searcher`. This also makes it possible to require Fennel modules from Lua (it will first look for a Lua
module of the same name when requiring from Lua).

This is automatic, but can be disabled by setting `g:fennel_nvim_patch_searchers` to 0 or `v:false` before any Fennel is invoked.

From `init.vim`:
```viml
let g:fennel_nvim_patch_searchers = v:false
```

## Lua API
**TODO:** Further document this API
The [fennel-nvim](lua/fennel-nvim.lua) Lua module offers an API you can use to eval/load/compile Lua.

```lua
local fnl = require('fennel-nvim')

fnl.dofile('path/to/file.fnl')

-- compile some Fennel into Lua for writing
local compiledLua = fnl.compile('path/to/file.fnl')
```

### Automatic package.path --> fennel.path sync

Because neovim sets `package.path` dynamically on the Lua side based on changes to the `runtimepath`
setting, I've implemented some code that syncs these changes over to `fennel.path`, replacing `?.lua`
with `?.fnl`, `/lua/?/init.lua` with `/fnl/?/init.fnl`, etc.

This behavior can be disabled before running any of the Fennel-executing Vim commands as follows:

```lua
local fnlNvim = require('fennel-nvim')
fnlNvim.syncFennelPath = false -- disabling syncing
fnlNvim.resetFennelPath() -- restore to state before sync
```

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