Skip to main content

Rendering Engine

lua_spa.renderer

The server-side template engine that converts .lspa templates into HTML before the page is sent to the browser.

Processing pipeline​

Each pass operates on the string produced by the previous pass. This ordering ensures:

  • Loop bodies can contain conditionals
  • Conditionals can contain {{ }} expressions
  • Expressions are always evaluated last on final content

render_template_with_directives(template, context)​

Main entry point. Accepts a template string and a context dict (props, state, py).

html = render_template_with_directives(
    "<p l-if=\"count > 0\">{{ count }}</p>",
    {"state": {"count": 3}, "props": {}, "py": {}}
)
# "<p>3</p>"

Loop expansion (i-for)​

Multi-target unpacking is supported:

<li i-for="i, item in enumerate(items)">{{ i }}: {{ item }}</li>

Nested loops work by re-running the pass until no more i-for attributes remain.

Conditional rendering (l-if)​

Interpolation ({{ }})​

All {{ expr }} tokens in the final string are replaced by evaluating expr in a safe Python context:

_SAFE_EVAL_GLOBALS = {
    "__builtins__": {},
    "range": range,
    "len": len,
    "enumerate": enumerate,
}

The template context adds state, props, and py on top of these globals.

Context object​

context = {
    "state":  {...},  # from client() state spec
    "props":  {...},  # from parent or initial_props
    "py":     {...},  # from context(props) return value
}

build_python_context(props, component) and build_server_state(component) in renderer.py assemble this dict before rendering.