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In this lesson, we’ll restrict the question references used in a page’s grading to only the questions on that page.
To do this, we need to define scope rules.

Oh my, you might think—this is going to be difficult. But with Freon we stick to the philosophy:
“Simple things should be simple, complex things should be possible.” (See our Background for more.)

Scoping answers the question: which names are visible where? In general, all names in a context are divided into sets.
These sets don’t overlap, but there are subsets within larger sets, as shown below.

Let’s say the smallest set that contains a name owns that name. For example, in the figure the name “Peter” is owned by set8.
Using common scoping rules, a name is visible in its owning set and in any set that contains the owning set, but not elsewhere.
So “Peter” would be visible in (from smallest to largest) set8, set4, set2, and set1, but not in set3, set5, set6, or set7.

Figure 1. Simple View on Namespaces

In Freon, these sets of names are called NameSpaces. Without any scope definitions, your editor has a single namespace containing every name in the model.

There’s an easy way to define additional namespaces in Freon. Any file that defines scoping must use the .scope extension.
Create a file called edu.scope.

First, think about the DSL: which names should be hidden in certain parts? Our problem is that question names are visible across all pages, not just the page where they’re defined.
That suggests the Page concept should be a namespace. Add the following to edu.scope:

// Education/lesson6-defs/edu.scope

scoper for language Education

isNamespace { Page  }

That’s it—easy peasy! Try it out: in a page’s Score, you can now only reference that page’s questions.

In the following lessons we’ll explore a few more scoping features. But first, we’ll define the last model unit: the Test unit.

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