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Scope hierarchies

This page covers organizing labels using scope blocks for encapsulation and namespace management. For label definition and reference syntax, see Symbol resolution. For the internal resolution algorithm, see Symbol resolution algorithm.

Scope declaration

Scopes create lexical namespaces using brace delimiters:

rem Anonymous scope

{
    <statements>
}

rem Named scope

<identifier>: {
    <statements>
}

Scope properties

  • Encapsulation: Labels defined in scope are local to that scope
  • Nesting: Scopes can contain nested scopes to arbitrary depth
  • Visibility: Inner scopes can reference outer scope labels
  • Shadowing: Local labels shadow identically-named labels in outer scopes

Scope chain example

global_label:
    print "global"

outer: {
    outer_label:
        print "outer"

    inner: {
        inner_label:
            print "inner"

        test:
            gosub inner_label       rem Resolves to inner.inner_label
            gosub outer_label       rem Resolves to outer.outer_label
            gosub global_label      rem Resolves to global scope
            return
    }
}

Shadowing and explicit scope reference

When a local label has the same name as a label in an outer scope, the local label shadows (hides) the outer one. The implicit global scope can be explicitly referenced using the global. prefix to access shadowed labels:

done:
    print "global done"
    return                          rem Global label

outer: {
    done:
        print "outer done"
        return                      rem Local label (shadows global)

    exit:
        gosub done                  rem Calls local outer.done
        gosub global.done           rem Explicitly calls global done
        return
}

From within outer.exit, an unqualified reference to done resolves to the local label. To explicitly access the shadowed done label in global scope, use the qualified reference global.done.

More in depth information can be found in the Symbol resolution algorithm chapter.

See also