## Postfix Syntax

Some languages are SOV — subject-object-verb — meaning the condition naturally comes before the keyword rather than after it. ForeignThon supports this with the `@@` operator.

---

## The problem

In English-order Python, the keyword always comes first:

```python
if condition:
    ...
```

In many languages, the natural order is the opposite — the condition is stated first, then the action. Forcing English word order on these languages makes the code feel unnatural.

---

## The solution

The `@@` operator lets you put any keyword after its expression:

```
condition @@keyword:
    body
```

This is equivalent to:

```
keyword condition:
    body
```

Both produce identical compiled Python. `@@` is purely a source-level syntax — it is processed before tokenization and never appears in the output.

---

## Rules

- `@@` rewrites only the line it appears on — nothing else changes
- Indentation follows standard Python rules, unchanged
- Prefix and postfix can be mixed freely in the same file
- Works for any keyword in any language pack
- `@@` is not valid Python syntax, so it never conflicts with existing code

---

## Supported constructs

| Construct | Prefix | Postfix |
|---|---|---|
| if | `keyword condition:` | `condition @@keyword:` |
| elif | `keyword condition:` | `condition @@keyword:` |
| while | `keyword condition:` | `condition @@keyword:` |
| def | `keyword name(args):` | `name(args) @@keyword:` |
| class | `keyword Name:` | `Name @@keyword:` |
| for | `keyword var in iter:` | `var @@in_kw iter @@for_kw:` |

!!! note
    `for` loops with postfix require two `@@` operators and can be complex. Most users keep `for` in prefix style.

---

## Decompile with postfix

When converting Python back to a foreign language, pass `--postfix`:

```bash
fpy decompile script.py --lang <code> --postfix
```

Which keywords get rewritten is controlled by the `postfix_keywords` list in the language pack JSON. A language that uses SVO order sets this to `[]` — postfix output is never forced on languages that don't need it.

```json
"postfix_keywords": ["if", "elif", "while", "def", "class"]
```

---

## Input vs output

| Direction | Mechanism | Controlled by |
|---|---|---|
| Input (writing `.xx.py`) | `@@` in source | Always available for any keyword |
| Output (`fpy decompile --postfix`) | Pack's `postfix_keywords` | Language pack author | Postfix Syntax