Value Subset - modelint/types GitHub Wiki

When we define a Component of a Type, we may also narrow down the set of values that can be assigned.

Let's say you are defining a cell location in a grid of rows and columns as we do in the Flatland diagram generator.

Cell 

  Row :: Integer(1, max)
  Col :: Integer(1, max)

Each of these two Components restricts the Integer Type to positive integers beginning from one. We aren't actually defining a new Type since all Integer operators still apply.

Though we could, instead, define a new User Type named Natural Number like so:

Natural Number

  Value :: Integer(1, max)

And then we could redefine Cell as follows:

Cell

  Row :: Natural Number
  Col :: Natural Number

In the new definition of Cell we don't further constrain the Component Types.

What's the difference, then, between a Value Subset and a Type?

A Type specifies both a set of assignable values and a set of Operators, while a Value Subset is simply a subset (possibly not a proper subset) of a selected Type. In other words, a Value Subset does not specify any Operator modifications.

Identifiers

1. Component + User type

Attributes

No non-referential attributes.