Templates & Projector Logic

Templates & Projector

The Projector (src/projector.rs) is the engine responsible for bridging the gap between Semantic Vyasa commands and the output (usually HTML).

Core Concept

Instead of hardcoding HTML generation in Rust (e.g. write!(w, "<h1>{}</h1>", title)), the compiler uses Templates defined in Vyasa itself (stdlib.vy or context.vy).

The Expansion Loop

1. Input: Semantic Node (e.g. `heading { The Title }).
2. Lookup: The Projector checks env.templates for a matching heading template.
3. Expansion: If found, it replaces the Semantic Node with the template’s body, interpolating variables.
4. Recursion: The output is processed again (allowing templates to use other templates).

Template Definition

Templates are defined using the template command (usually sugar syntax in .vy):

`template { target="heading"
    `h2 { $.text }
}

Interpolation Syntax

• $.text: Replaced by the semantic command’s children.
• $.var: Replaced by the value of attribute var from the semantic command.
• $.context.key: (Advanced) Access global context.

Control Flow

The Projector supports basic logic:

if Command

Conditionals based on attribute values.

`if { lhs="$.type" op="eq" rhs="warning"
    `div { class="alert warning" ... }
}

each Command

Iterating over lists (collections).

`each { "work.chapters"
    `li {
        `a { href="$.url" $.title }
    }
}

View vs Collection Templates

• View Template: Used to render a single source file. Defines the body command behavior.
• Collection Template: Used to generate an index page (e.g. Table of Contents) by iterating over build stats (work.items).