moon_tera

A Tera 2.0-style template engine for MoonBit — VM-architected, ported from Keats/tera.

moon_tera brings a mature, Jinja2/Tera-flavored template engine to the MoonBit ecosystem. It targets static site generation (SSG), web/server-side rendering, and config / LLM-prompt templating.

It is a from-scratch port of Tera 2.0’s architecture, adapted to MoonBit’s type system: no serde; a native Value data model with @json interop.

✨ Features

Expressions {{ ... }} with a Pratt parser: literals, variables, member access (a.b), arithmetic (+ - * / %), comparisons (== != < > <= >=), logic (and / or / not), is tests, and | filters (chainable)
Control flow {% if/elif/else %}, {% for x in xs %}, {% set %} (planned)
Template inheritance {% extends "base" %} / {% block name %} — child blocks override ancestors
Includes {% include "partial" %}
26+ filters: upper lower trim length default first last abs reverse nth int round keys values json_encode escape_html capitalize concat unique slice replace split join sort title striptags
13 is tests: odd even defined undefined string number integer float bool array object empty iterable
Bytecode VM architecture (Parser → Compiler → Interpreter); the compile/run path is wired up, M1.5 renders via an AST-walk interpreter
Autoescape foundation (escape_html / e); whitespace control; comments {# #}

🔨 Build & Test

moon check            # type-check
moon build            # build (default target: wasm-gc)
moon test             # run all tests (40+)
moon test --target all   # all backends (wasm-gc / js / native)

📦 Quick example

let tera = Tera::new()
tera.add_template("base", "<h1>{% block title %}Blog{% endblock %}</h1>")
tera.add_template("post", "{% extends \"base\" %}{% block title %}{{ title | upper }}{% endblock %}")
let ctx = object_value([("title", str_value("hello"))])
tera.render("post", ctx)  // => "<h1>HELLO</h1>"

🧭 Architecture

source --lex--> Tokens --parse--> AST --render--> String
                                 (extends/block/include resolved via Tera registry)

File	Responsibility
`value.mbt`	JSON-like `Value` data model + truthiness
`lexer.mbt` / `token.mbt`	template-level lexer (text / `{{ }}` / `{% %}` / `{# #}`)
`expr.mbt`	expression sub-language lexer + Pratt parser
`parser.mbt`	recursive-descent parser → AST
`vm.mbt`	AST-walk interpreter (M2: bytecode VM)
`filters.mbt` / `is_tests.mbt`	filter and test libraries
`tera.mbt`	engine: template registry + inheritance chain resolution

🆚 Differentiation vs `moonjinja`

	moon_tera	moonjinja
Architecture	bytecode VM (in progress)	AST-walk
Inheritance	extends / block / override	single-layer block
Includes	✓	✓
Filters	26+	5
`is` tests	13	0
Floats / elif / block-set	✓	✗
Tests	40+ precise	4 substring

📄 License

MIT. Derivative port of Keats/tera (MIT); see LICENSE and NOTICE. Original copyright preserved.

🚧 Status

Built for the 2026 CCF × MoonBit open-source ecosystem contest. Roadmap: M0 scaffold ✓ · M1 render pipeline ✓ · M2 filters/tests ✓ (ongoing) · M3 inheritance/include ✓ · M4 SSG demo + polish (ongoing).