MTLQuery

struct MTLQuery

Overview

Queries provide reusable computation logic in MTL modules, extending AQL with custom operations that can be invoked from templates and other queries. Unlike templates, queries do not generate text output.

Overview

MTL queries serve multiple purposes:

• Code reuse: Complex expressions can be encapsulated and reused

• Type extension: New operations can be added to existing types

• Modularity: Complex templates can be broken down into manageable functions

• Testing: Individual query functions can be tested independently

Side-Effect Freedom

Queries must be side-effect-free, meaning they:

• Do not modify model elements

• Do not write to files or output

• Only compute and return values

• Can be safely cached and memoized

Example Usage

// Simple query
let fullNameQuery = MTLQuery(
    name: "fullName",
    parameters: [
        MTLVariable(name: "person", type: "Person")
    ],
    returnType: "String",
    body: MTLExpression(AQLBinaryExpression(
        left: AQLNavigationExpression(
            source: AQLVariableExpression(name: "person"),
            property: "firstName"
        ),
        right: AQLNavigationExpression(
            source: AQLVariableExpression(name: "person"),
            property: "lastName"
        ),
        op: .concat
    ))
)

// Type-checking query
let isPublicQuery = MTLQuery(
    name: "isPublic",
    parameters: [MTLVariable(name: "element", type: "Element")],
    returnType: "Boolean",
    body: MTLExpression(AQLNavigationExpression(
        source: AQLVariableExpression(name: "element"),
        property: "visibility"
    ))
)