flow-website/content/docs/architecture/command.smd

---
.title = "Commands",
.date = @date("2025-10-15T00:00:00"),
.author = "Igor Támara",
.layout = "tutorial.shtml",
.draft = false,
.custom = {
  .githubedit = "/docs/architecture/command.smd",
  .codepath = "src/tui/editor.zig",
},
---

Commands are actions triggered to operate on buffers primarily. They are
present in `editor`, `tui`, `mode` and `minimodes`, it's possible to
find commands in other places, which will become evident when the need
arises.

[]($section.id('notes'))
## Previous notes

Note: Flow is programmed with [zig](https://ziglang.org/), if you are
familiar with C, C++, Rust, there are differences and reasonings that
might find useful when [learning Zig](https://ziglang.org/learn/). If
you are coming from higher level programming languages such as Python,
Ruby, C#, Java, Golang, Typescript it will be an opportunity to learn
about trades of managing memory and fast responses and some lower level
concepts present in Zig. If you are brand new to programming, some
general concepts will be needed and practice in another language before
getting into flow development.

If you are new to Zig, it's a good idea to take a look at
[ziglings](https://ziglings.org/) to practice, as you learn the
language.

Maybe there is a [shell command invoked](/docs/architecture/keybind#shell)
with a keybinding that can help in the task you are aiming at before
developing flow itself.

[]($section.id('creating'))
## Understanding and creating commands

A command is a function with a type like

```zig
pub fn copy(self: *Self, _: Context) Result
```

and a `Meta` definition with the same name and suffix `_meta`.

```zig
pub const copy_meta: Meta = .{ .description = "Copy selection to clipboard" };
```

`copy` command is defined in `editor.zig`, which copies the current
selections into the pimp internal clipboard. Commands are available to
all the modes if defined as `pub`.

`meta` holds the description appearing in the command palette and
optionally has arguments, the most common, an integer, that usually
constitutes a repetition parameter, targeting vim, emacs and helix
modes. As you dig in, there might be particularities on the parameters
accepted for a given command.

[]($section.id('calling'))
## Invoking another command

Commands can be bound to mnemonics in modes by convention. For example,
in Vim Mode `vim.zig`, `q` corresponds to (quit), the most famous one.

```zig
pub fn q(_: *void, _: Ctx) Result {
    try cmd("quit", .{});
}
pub const q_meta: Meta = .{ .description = "q (quit)" };
```

Looking more closely, the first parameter in this case is of `*void`
type, given that this command is defined in `vim.zig` which is calling
the `quit` command defined in `editor.zig`. `cmd` takes care of routing
and finding the command wherever it is defined.

[]($section.id('tldr'))
## Chaining commands

Chaining commands is also common, and, by the way, swift. This is a
sample of applying first `save_file` command and then, the command
`quit`.

```zig
pub fn wq(_: *void, _: Ctx) Result {
    try cmd("save_file", command.fmt(.{ "then", .{ "quit", .{} } }));
}
pub const wq_meta: Meta = .{ .description = "wq (write file and quit)" };
```

`cmd` is in charge of finding a command given its name, and parameters
sent to commands vary for each command.

Sometimes [keybinding](/docs/architecture/keybind) is enough to
accomplish a compound of already present commands.

[]($section.id('deepen'))
## Code organization

Is common to define private functions in a given module that are
invoked from commands, as usual, functions are meant to be reused and
help organize code.

For example, in hx mode `helix.zig` the `select_to_char_left_helix`
command uses the functions `helix_with_selections_const_arg` which
iterates over all cursels and applies the
`select_cursel_to_char_left_helix` function.

```zig
pub fn select_to_char_left_helix(_: *void, ctx: Ctx) Result {
    try helix_with_selections_const_arg(ctx, &select_cursel_to_char_left_helix);
}
```

[]($section.id('command_arguments'))
### Sending parameters to commands

`goto_line` (in the case of vim and helix mode, you first type the
number and then the action, `gg`) is a command that exemplifies
receiving an integer parameter as stated in its meta:

```zig
pub const goto_line_meta: Meta = .{ .arguments = &.{.integer} };
```

and to actually receiving the integer parameter, `goto_line` will
extract it like this:

```zig
pub fn goto_line(self: *Self, ctx: Context) Result {

    var line: usize = 0;
    if (!try ctx.args.match(.{tp.extract(&line)}))
        return error.InvalidGotoLineArgument;
```

To send a parameter to a command, make sure that the type is exactly
the same when retrieving it. We will refer as encode and decode. Hence
for our terminology to send an integer parameter to a command, we
will encode it using `command.fmt` like in

```zig
var the_line: usize = 43;
try ed.goto_line(command.fmt(.{the_line - 1}));
```

It's possible to pass multiple parameters to commands, including arrays
and json, they all will be packed in Command.Context.

A deeper explanation of the rules about parameter passing is exposed in
[inner data exchange](/docs/architecture/inner_data_exchange).

[]($section.id('next'))
## Next steps

* [minimode](/docs/architecture/minimode) shows argument passing to
commands in reaction to keypresses.
* [Palettes](/docs/architecture/palette) invoke commands and pass
parameters to them.
* [Add tests](/docs/testing) to harden your code
* [Back to architecture](/docs/architecture)