# Smalto
[](https://hex.pm/packages/smalto)
[](https://hexdocs.pm/smalto/)
[](https://conventionalcommits.org)
[](https://www.erlang.org/)
[](https://codeberg.org/veeso/smalto)
[](https://github.com/veeso/smalto/actions/workflows/smalto.yml)
[](https://github.com/veeso/smalto/actions/workflows/smalto-lustre.yml)
[](https://github.com/veeso/smalto/actions/workflows/js-tools.yml)
A general-purpose syntax highlighting library for Gleam, with regex-based grammars for 30+ languages.
Smalto tokenizes source code using regex-based grammar definitions inspired by [Prism.js](https://prismjs.com/), with output to structured tokens, ANSI terminal colors, or HTML with CSS classes.
## Features
- Regex-based tokenizer engine with greedy matching and nested grammar support
- 30 built-in languages including Gleam, Rust, Python, JavaScript, HTML, CSS, and more
- Three output formats: tokens, ANSI terminal colors, HTML with CSS classes
- Language inheritance (e.g., TypeScript extends JavaScript)
- Nested tokenization for embedded languages (e.g., CSS inside HTML)
- Hybrid token types: well-known semantic variants plus a `Custom` escape hatch
- [Lustre integration](#lustre-integration) via the [`smalto_lustre`](https://hex.pm/packages/smalto_lustre) package
## Installation
```sh
gleam add smalto@1
```
## Quick start
```gleam
import smalto
import smalto/languages/python
pub fn main() {
let code = "
def greet(name: str) -> str:
\"\"\"Return a greeting.\"\"\"
return f'Hello, {name}!'
"
// Highlight to HTML
let html = smalto.to_html(code, python.grammar())
// Highlight to ANSI terminal colors
let ansi = smalto.to_ansi(code, python.grammar())
// Get raw tokens for custom processing
let tokens = smalto.to_tokens(code, python.grammar())
}
```
### HTML output
The HTML renderer wraps each token in a `<span>` with a CSS class. Place the output within `<pre><code>...</code></pre>` and style the classes:
```css
pre code .smalto-keyword { color: #ffd596; }
pre code .smalto-string { color: #c8ffa7; }
pre code .smalto-number { color: #c8ffa7; }
pre code .smalto-comment { color: #d4d4d4; font-style: italic; }
pre code .smalto-function { color: #9ce7ff; }
pre code .smalto-operator { color: #ffaff3; }
pre code .smalto-type { color: #ffddfa; }
pre code .smalto-module { color: #ffddfa; }
pre code .smalto-tag { color: #ff6b6b; }
pre code .smalto-attribute { color: #ffd596; }
pre code .smalto-selector { color: #9ce7ff; }
pre code .smalto-property { color: #ffd596; }
```
## Supported languages
| Language | Module | Extends |
| ---------- | -------- | --------- |
| Bash | `smalto/languages/bash` | |
| C | `smalto/languages/c` | |
| C++ | `smalto/languages/cpp` | C |
| CSS | `smalto/languages/css` | |
| Dart | `smalto/languages/dart` | |
| Dockerfile | `smalto/languages/dockerfile` | |
| Elixir | `smalto/languages/elixir` | |
| Erlang | `smalto/languages/erlang` | |
| Gleam | `smalto/languages/gleam` | |
| Go | `smalto/languages/go` | |
| Haskell | `smalto/languages/haskell` | |
| HTML | `smalto/languages/html` | |
| Java | `smalto/languages/java` | |
| JavaScript | `smalto/languages/javascript` | |
| JSON | `smalto/languages/json` | |
| Kotlin | `smalto/languages/kotlin` | |
| Lua | `smalto/languages/lua` | |
| Markdown | `smalto/languages/markdown` | |
| PHP | `smalto/languages/php` | |
| Python | `smalto/languages/python` | |
| Ruby | `smalto/languages/ruby` | |
| Rust | `smalto/languages/rust` | |
| Scala | `smalto/languages/scala` | |
| SQL | `smalto/languages/sql` | |
| Swift | `smalto/languages/swift` | |
| TOML | `smalto/languages/toml` | |
| TypeScript | `smalto/languages/typescript` | JavaScript |
| XML | `smalto/languages/xml` | |
| YAML | `smalto/languages/yaml` | |
| Zig | `smalto/languages/zig` | |
## Lustre integration
The [`smalto_lustre`](https://hex.pm/packages/smalto_lustre) package renders tokens as [Lustre](https://hexdocs.pm/lustre/) `Element` nodes:
```sh
gleam add smalto smalto_lustre
```
```gleam
import smalto
import smalto/languages/python
import smalto/lustre as smalto_lustre
let tokens = smalto.to_tokens("print('hello')", python.grammar())
let elements = smalto_lustre.to_lustre(tokens, smalto_lustre.default_config())
```
The default config uses inline-styled `<span>` elements matching smalto's ANSI color scheme. Customize individual token renderers with the builder functions. See the [`smalto_lustre` README](smalto_lustre/) for full details.
## Try it out
Smalto ships with example tools in the `dev/` directory:
```sh
# Print syntax-highlighted source to the terminal using ANSI colors
gleam run -m cat -- path/to/file.py
# Render a standalone HTML file with an embedded CSS theme
gleam run -m html_render -- path/to/file.py dracula output.html
```
The `cat` tool detects the language from the file extension and prints highlighted output to stdout. The `html_render` tool does the same but writes a self-contained HTML file using one of the 45 bundled CSS themes (see `themes/` directory).
## Documentation
API reference is available on [HexDocs](https://hexdocs.pm/smalto/).
## Development
```sh
gleam build # Compile the project
gleam test # Run the tests
gleam format src test # Format code
```
### Prism.js converter
Language grammars are generated from [Prism.js](https://prismjs.com/) definitions using a Node.js converter tool:
```sh
cd tools/prism_converter
npm install
node convert.js python rust javascript # Convert specific languages
node convert.js --all # Convert all target languages
```
## License
Smalto is licensed under the MIT License. See [LICENSE](LICENSE) for details.
