# PPX rewriter

The `ocsigen-i18n-rewriter` PPX extension transforms `[%i18n ...]` expressions into calls to the generated translation functions.


## Setup

Add the PPX to your dune file:

```
(preprocess (pps ocsigen-i18n -- --default-module MyI18n))
```
where `MyI18n` is the name of the module generated by `ocsigen-i18n-generator` (the basename of the output file, capitalized).

Without dune, use:

```
-ppx 'ocsigen-i18n-rewriter --default-module MyI18n'
```

## Expressions

The PPX supports the following forms:

| Expression | Meaning |
| --- | --- |
| `[%i18n foo]` | Calls `MyI18n.Tr.foo ()` (HTML) |
| `[%i18n S.foo]` | Calls `MyI18n.S.foo ()` (string) |
| `[%i18n bar ~x:expr]` | Passes a labelled argument |
| `[%i18n OtherMod.foo]` | Calls `OtherMod.Tr.foo ()` |
| `[%i18n OtherMod.S.foo]` | Calls `OtherMod.S.foo ()` |

## Module affixing

To avoid redundancy when using multiple i18n modules, you can auto-prefix and auto-suffix module names:

```
(preprocess (pps ocsigen-i18n -- --default-module MyI18n --prefix Pr_ --suffix _i18n))
```
With this configuration, `[%i18n Feature.foo]` becomes `Pr_Feature_i18n.Tr.foo ()`.

**Important:** Do not name your i18n file `s.tsv`, as `S` is reserved for the string module.