Contexts

A context bundles macros, constants, words, and other declarations into an isolated namespace. It is the primary mechanism for creating domain-specific languages (DSLs) in Zith.

Defining & Using a Context

A context is activated with use, either scoped to a block or globally (one active per category at a time).

use SQL QueryBlock {
    SELECT * FROM users WHERE id = :id
}

use SQL;   // global activation — replaces previous context

Context-Bound Extensibility (Best Practice)

Macros and words should ideally live inside a context block. Activating them globally is possible but discouraged — similar to using namespace std; in C++.

// Preferred
use SQL QueryBlock {
    // SQL words and macros active only here
}

// Discouraged
use SQL;   // pollutes the rest of the file

Contexts with Macros

context WebApp {
    // Macros scoped to this context
    macro @getParam(name) { request.params[name] }

    // Constants
    const VERSION = "1.0";

    // Custom keywords
    macro @async { /* async handling */ }
}

// Activate in a block
use WebApp {
    let version = VERSION;
    let param = @getParam("name");
}
// Outside, WebApp syntax is not available

Nesting Contexts

All named blocks in Zith may receive a context. Contexts can be nested:

use Web {
    use Database {
        // Both Web and Database syntax available
    }
}

Tag Macros — HTML-like DSL Syntax

Tag macros let you define XML/HTML-like syntax inside a context. They expand at compile time into function calls.

context HTML {
    tag macro div(content) { "<div>" + content + "</div>" }
    tag macro span(content) { "<span>" + content + "</span>" }
    tag macro a(href: string, content) {
        "<a href=\\"" + href + "\\">" + content + "</a>"
    }
}

use HTML { <div> <span>Hello</span> <a href="/">Home</a> </div> }

// Expands at compile time to:
// "<div><span>Hello</span><a href=\"/\">Home</a></div>"

Tag macros are pure compile-time expansions — no runtime parsing, no injection vulnerabilities. The arguments are type-checked Zith expressions.

Use Cases

• Web Development: HTML templating, HTTP routing DSLs
• Database: SQL query building with compile-time validation
• Graphics: Shader definitions, scene descriptions
• Configuration: Custom configuration file parsers

See also: Spec: Contexts

Related: Macros | Type System