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  • Shapes - an introductory MPS tutorial

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Since we would like to allow the users of our language to pick the color for the shape from a list of pre-defined colors, we can't just use a textual property to hold the color value. Instead we'll add a reference to Shape and have this reference point to one of the pre-defined color constants. Let's start with creating such constants that will represent pre-defined colors.

Concept for colors

One way would be to use MPS enums to define the colors. This would, however, not allow users to define their own colors. All the colors would be defined in the enum that would be a part of the Shapes language. Instead, we will use full a blown concept for colors and nodes of that concept will define the individual colors. These color nodes can be defined as part of the language (inside so called accessory models) or directly in user models next to instances of the Canvas concept.

First we're going to create a concept that will represent a color constant. We'll call it Color and it will be rootable, so that we can place it inside models:

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