Rules of Marble diagrams

To draw a Marble diagram to represent an FRP operation in a pictorial form, we should follow these rules:

A horizontal line represents a data stream:

That horizontal line represents a duration or time from left to right to perform that data transformation operation.

Some symbols (such as circles, diamonds, and rectangles) on top of that horizontal line are used to represent the data elements coming from a source data stream or resulting data elements on the destination data stream:

We can use any symbol to represent the data elements in a Marble diagram:

The big rectangular box in the center of a Marble diagram represents the actual data transformation (or functional operation, Reactive operation, or FRP operation) logic:

The top horizontal line represents the Source Data Stream, and the bottom horizontal line represents the Destination Data Stream (or resulting data stream):

The vertical line (|) on top of the horizontal line represents the data stream completing successfully:

A cross mark (X) on top of the horizontal line represents that the data stream is completed with errors:

We can say that these are the properties of a Marble diagram. We will explore these rules with some useful examples in subsequent sections.