helix/book/src/usage.md

# Using Helix

<!--toc:start-->
- [Registers](#registers)
  - [User-defined registers](#user-defined-registers)
  - [Special registers](#special-registers)
- [Surround](#surround)
- [Selecting and manipulating text with textobjects](#selecting-and-manipulating-text-with-textobjects)
- [Navigating using tree-sitter textobjects](#navigating-using-tree-sitter-textobjects)
- [Moving the selection with syntax-aware motions](#moving-the-selection-with-syntax-aware-motions)
<!--toc:end-->

For a full interactive introduction to Helix, refer to the
[tutor](https://github.com/helix-editor/helix/blob/master/runtime/tutor) which
can be accessed via the command `hx --tutor` or `:tutor`.

> 💡 Currently, not all functionality is fully documented, please refer to the
> [key mappings](./keymap.md) list.

## Registers

In Helix, registers are storage locations for text and other data, such as the
result of a search. Registers can be used to cut, copy, and paste text, similar
to the clipboard in other text editors. Usage is similar to Vim, with `"` being
used to select a register.

### User-defined registers

Helix allows you to create your own named registers for storing text, for
example:

- `"ay` - Yank the current selection to register `a`.
- `"op` - Paste the text in register `o` after the selection.

If a register is selected before invoking a change or delete command, the selection will be stored in the register and the action will be carried out:

- `"hc` - Store the selection in register `h` and then change it (delete and enter insert mode).
- `"md` - Store the selection in register `m` and delete it.

### Special registers

| Register character | Contains              |
| ---                | ---                   |
| `/`                | Last search           |
| `:`                | Last executed command |
| `"`                | Last yanked text      |
| `_`                | Black hole            |

The system clipboard is not directly supported by a special register. Instead, special commands and keybindings are provided. Refer to the
[key map](keymap.md#space-mode) for more details.

The black hole register is a no-op register, meaning that no data will be read or written to it.

## Surround

Helix includes built-in functionality similar to [vim-surround](https://github.com/tpope/vim-surround).
The keymappings have been inspired from [vim-sandwich](https://github.com/machakann/vim-sandwich):

![Surround demo](https://user-images.githubusercontent.com/23398472/122865801-97073180-d344-11eb-8142-8f43809982c6.gif)

| Key Sequence                      | Action                                  |
| --------------------------------- | --------------------------------------- |
| `ms<char>` (after selecting text) | Add surround characters to selection    |
| `mr<char_to_replace><new_char>`   | Replace the closest surround characters |
| `md<char_to_delete>`              | Delete the closest surround characters  |

You can use counts to act on outer pairs.

Surround can also act on multiple selections. For example, to change every occurrence of `(use)` to `[use]`:

1. `%` to select the whole file
2. `s` to split the selections on a search term
3. Input `use` and hit Enter
4. `mr([` to replace the parentheses with square brackets

Multiple characters are currently not supported, but planned for future release.

## Selecting and manipulating text with textobjects

In Helix, textobjects are a way to select, manipulate and operate on a piece of
text in a structured way. They allow you to refer to blocks of text based on
their structure or purpose, such as a word, sentence, paragraph, or even a
function or block of code.

![Textobject demo](https://user-images.githubusercontent.com/23398472/124231131-81a4bb00-db2d-11eb-9d10-8e577ca7b177.gif)
![Textobject tree-sitter demo](https://user-images.githubusercontent.com/23398472/132537398-2a2e0a54-582b-44ab-a77f-eb818942203d.gif)

- `ma` - Select around the object (`va` in Vim, `<alt-a>` in Kakoune)
- `mi` - Select inside the object (`vi` in Vim, `<alt-i>` in Kakoune)

| Key after `mi` or `ma` | Textobject selected      |
| ---                    | ---                      |
| `w`                    | Word                     |
| `W`                    | WORD                     |
| `p`                    | Paragraph                |
| `(`, `[`, `'`, etc.    | Specified surround pairs |
| `m`                    | The closest surround pair    |
| `f`                    | Function                 |
| `t`                    | Type (or Class)          |
| `a`                    | Argument/parameter       |
| `c`                    | Comment                  |
| `T`                    | Test                     |
| `g`                    | Change                   |

> 💡 `f`, `t`, etc. need a tree-sitter grammar active for the current
document and a special tree-sitter query file to work properly. [Only
some grammars][lang-support] currently have the query file implemented.
Contributions are welcome!

## Navigating using tree-sitter textobjects

Navigating between functions, classes, parameters, and other elements is
possible using tree-sitter and textobject queries. For
example to move to the next function use `]f`, to move to previous
type use `[t`, and so on.

![Tree-sitter-nav-demo][tree-sitter-nav-demo]

For the full reference see the [unimpaired][unimpaired-keybinds] section of the key bind
documentation.

> 💡 This feature relies on tree-sitter textobjects
> and requires the corresponding query file to work properly.

## Moving the selection with syntax-aware motions

`Alt-p`, `Alt-o`, `Alt-i`, and `Alt-n` (or `Alt` and arrow keys) allow you to move the 
selection according to its location in the syntax tree. For example, many languages have the
following syntax for function calls:

```js
func(arg1, arg2, arg3);
```

A function call might be parsed by tree-sitter into a tree like the following.

```tsq
(call
  function: (identifier) ; func
  arguments:
    (arguments           ; (arg1, arg2, arg3)
      (identifier)       ; arg1
      (identifier)       ; arg2
      (identifier)))     ; arg3
```

Use `:tree-sitter-subtree` to view the syntax tree of the primary selection. In
a more intuitive tree format:

```
            ┌────┐
            │call│
      ┌─────┴────┴─────┐
      │                │
┌─────▼────┐      ┌────▼────┐
│identifier│      │arguments│
│  "func"  │ ┌────┴───┬─────┴───┐
└──────────┘ │        │         │
             │        │         │
   ┌─────────▼┐  ┌────▼─────┐  ┌▼─────────┐
   │identifier│  │identifier│  │identifier│
   │  "arg1"  │  │  "arg2"  │  │  "arg3"  │
   └──────────┘  └──────────┘  └──────────┘
```

If you have a selection that wraps `arg1` (see the tree above), and you use
`Alt-n`, it will select the next sibling in the syntax tree: `arg2`.

```js
// before
func([arg1], arg2, arg3)
// after
func(arg1, [arg2], arg3);
```

Similarly, `Alt-o` will expand the selection to the parent node, in this case, the
arguments node.

```js
func[(arg1, arg2, arg3)];
```

There is also some nuanced behavior that prevents you from getting stuck on a
node with no sibling. When using `Alt-p` with a selection on `arg1`, the previous
child node will be selected. In the event that `arg1` does not have a previous
sibling, the selection will move up the syntax tree and select the previous
element. As a result, using `Alt-p` with a selection on `arg1` will move the
selection to the "func" `identifier`.

[lang-support]: ./lang-support.md
[unimpaired-keybinds]: ./keymap.md#unimpaired
[tree-sitter-nav-demo]: https://user-images.githubusercontent.com/23398472/152332550-7dfff043-36a2-4aec-b8f2-77c13eb56d6f.gif