# Emacs mode for Klammertext

`klammertext-mode.el` is an Emacs major mode for editing Klammertext files.  It
helps Klammertext authors see the structure of klammer application through
syntax highlighting.

## Install

Put the `emacs` directory somewhere on your system, then tell Emacs where it is
and load the mode. Add to `~/.emacs.d/init.el`:

```elisp
(add-to-list 'load-path "full-pathname-of-the-emacs-directory")
(require 'klammertext-mode)
```

Replace `full-pathname-of-the-emacs-directory` with the full path to the
directory that contains `klammertext-mode.el`.

The mode auto-activates for `.kt` and `.k` files. (The `.k` / `.kt` distinction
is a filing convention, not a lexical one — the same mode serves both.) You can
also switch to it manually with `M-x klammertext-mode`.

## What it highlights

**Text-removal ("ignore") constructs** — in two independently chosen colors,
one for the *removed content*, one for the *marker characters*:

| Construct    | Meaning                          |
|--------------|----------------------------------|
| `#` ...      | remove to end of line            |
| `##` ...     | remove to end of buffer          |
| `#[ ... ]#`  | remove enclosed text (nestable)  |

**Klammer applications** — in two independent colors: one for *opening* a
klammer, one for *closing* it. The `@` and the name of an opening are one
syntactic unit and share the opening color; the close (named or bare) gets the
closing color, so you always have visual confirmation of where a klammer ends:

| Form      | Color   | Meaning                          |
|-----------|---------|----------------------------------|
| `@name`   | opening | opening `@` + name (one unit)    |
| `name@`   | closing | named closing delimiter          |
| `@`       | closing | bare closing delimiter           |

In the abbreviated form `@name-arg1-arg2` (equivalent to `@name arg1 | arg2 @`)
only the name is colored — the name ends at the first hyphen, and the
hyphen-separated arguments stay plain, just as `arg1`/`arg2` would be plain in
the long form.

Because a named closing carries the closing color across its name too, long
klammers that name their closing delimiter (`@document ... document@`) stand
out — which is exactly where naming the closing delimiter earns its keep
(accurate unmatched-delimiter error messages). Short bodies (`@i word @`) are
conventionally left with a bare `@` to keep the text uncluttered.

**Klammer definitions** (`@@`) are highlighted the same way, in their own pair
of colors — so definitions read as distinct from applications at a glance:

| Form       | Color   | Meaning                           |
|------------|---------|-----------------------------------|
| `@@name`   | opening | opening `@@` + name (one unit)    |
| `name@@`   | closing | named closing delimiter           |
| `@@`       | closing | bare closing delimiter            |

The name ends at the first non-name character, so a target suffix like
`@@name.html` colors only `@@name` and leaves `.html` plain. A definition's
body (between `@@name` and the closing `@@`) is highlighted like ordinary
Klammertext — e.g. an `@i … @` inside it shows as a normal application.

**System/target commands** (`@@@`) — `@@@target`, `@@@argtype`, `@@@state` — get
a third pair of colors, so the three `@`-levels (application, definition, system)
are visually distinct:

| Form       | Color   | Meaning                           |
|------------|---------|-----------------------------------|
| `@@@name`  | opening | opening `@@@` + name (one unit)   |
| `name@@@`  | closing | named closing delimiter           |
| `@@@`      | closing | bare closing delimiter            |

`@@@` commands do not nest, so each delimiter is colored independently; their
bodies (`| … |` option lists) are highlighted as ordinary Klammertext.

## The eight faces

All eight faces are defined by the `defconst klammertext--palette` at the
beginning of `klammertext-mode.el`.

| Face                              | Applies to                          |
|-----------------------------------|-------------------------------------|
| `klammertext-ignored-face`        | removed content                     |
| `klammertext-marker-face`         | `#`, `##`, `#[`, `]#`              |
| `klammertext-klammer-open-face`   | an application opening `@name`      |
| `klammertext-klammer-close-face`  | an application close `name@` or `@` |
| `klammertext-def-open-face`       | a definition opening `@@name`       |
| `klammertext-def-close-face`      | a definition close `name@@` or `@@` |
| `klammertext-system-open-face`    | a system opening `@@@name`          |
| `klammertext-system-close-face`   | a system close `name@@@` or `@@@`   |

To experiment with a color (evaluate in `*scratch*`, or add to your init):

```elisp
(set-face-foreground 'klammertext-marker-face "cyan")
(set-face-foreground 'klammertext-system-close-face "chocolate4")
```

or `M-x customize-face RET klammertext-marker-face RET`.

## Matching delimiters (show-paren)

With `show-paren-mode` on (the default in Emacs 28+), placing point on a klammer
**application** delimiter highlights its partner, in both directions: on an
opening `@name` it highlights the closing `@`/`name@`, and on a close it
highlights the opening `@name`. Nesting is respected — in `@a @b x @ @`, the
outer `@a` matches the last `@`, not the first.

Matching covers applications only (`@`), not `@@`/`@@@`, since that is where
paired delimiters matter most. The matcher steps over `@@`/`@@@`, removed text,
other literal spans and escaped `^@`; the abbreviated `@name-arg` form has no
closing delimiter, so nothing is highlighted on it.

**Literal klammers** (those in `klammertext-literal-klammers`, e.g. `@code`) are
closed with the full `NAME@` form because their content is verbatim. These are
matched *by name* — `@code` ↔ `code@` — with the content treated as opaque, so a
stray `@` inside (`@code x @ y code@`) doesn't confuse the match, in either
direction. Register any klammer that declares a `literal` argument with
`(klammertext-add-literal-klammer "name")` in your init file so both its
highlighting and its delimiter matching work.

If a **named** close disagrees with its opening — e.g. `@doc … foo@` (should be
`doc@`) — the mismatched delimiter is shown in **bright red** (bold), and a
message describing the mismatch appears in the minibuffer, e.g.

> `Klammertext: closing foo@ does not match opening @doc`

An unbalanced delimiter (an opening with no close, or vice versa) is flagged the
same way. This turns the naming convention into a live check: name a long
klammer's closing delimiter and a typo'd or unbalanced name lights up
immediately. The red comes from `klammertext-mismatch-face`, which is remapped
over `show-paren-mismatch` **only in Klammertext buffers** (your global
`show-paren-mismatch` face is left untouched); customize it to taste.

This is wired in automatically (`show-paren-data-function`); you only need
`show-paren-mode` enabled. It relies on nothing in the syntax table — Klammertext
delimiters can't be expressed there — so it does not interfere with other
`@`/`#` characters.

### Jumping between matches

`klammertext-jump-to-match`, bound to **`C-c C-j`**, moves point to the matching
delimiter: from an opening `@name` to its close, and from a close back to its
opening `@name`. It uses the same matcher as the highlighting. The starting
position is pushed to the mark ring, so `C-u C-SPC` jumps back. (Also available
as `M-x klammertext-jump-to-match`.)

## Literal klammers

Inside a `literal` argument — for example the body of `@code ... code@` — `#`
and `@` are literal text, not Klammertext syntax. The mode highlights the
opening `@code` and closing `code@` but leaves the interior as normal text,
for any klammer registered in `klammertext-literal-klammers`. `@code` is
registered by default.

If you define your own klammer with a `literal` parameter (a relatively
advanced action — see the `literal` argument type in the project
documentation), register it in your init file:

```elisp
(klammertext-add-literal-klammer "myverbatim")
```

Because the list is consulted at fontification time, registering a klammer
while a buffer is already open takes effect after `M-x font-lock-update` (or
re-visiting the file).

## Known limitations (deliberate, for now)

- Unescaped `@` is always treated as a delimiter (as the Klammermachine does),
  so an `@` in prose that is *not* meant as a klammer — e.g. an email address
  written `foo@bar` instead of `foo^@bar` — will be highlighted. This reflects
  what the machine actually sees.
- Very large multiline blocks or literal spans edited far from their opening
  may occasionally need `M-x font-lock-update` to re-highlight correctly.