\open_arrow

Description 

\open_arrow operator draws the symbol to open the model following the arrow. The open symbol is usually represented as a white filled troncated arrow. This operator takes two arguments:

• an edge: the edge on which the symbol is drawn,
• a side keyword: left/right to specify where to draw the arrow according to the given edge. This parameter is optional and the default value is right.

The open arrow symbol is drawn at the middle of the given edge. Doodle checks if the given edge has been defined, if this is not the case an error occurs.
WARNING: the order to specify the edge is important because it is used to know which side is the left or right side.
Therefore, \open_arrow([a, b], left); doesn't produce the same result as \open_arrow([b, a], left);.
This operator should only appear within a step block.

Figure: Example of an open arrow usage using the \open_arrow operator. This figure presents a squash fold, with the open action of the right part.

Usage

  \open_arrow([b, a]); % right is default 
  \open_arrow([a, b], left); % same as above

Formal structure

  \open_arrow(EDGE, SIDE);
  \open_arrow(EDGE);

Parameters

  EDGE
  Description    : Indicates the edge on which the arrow is drawn.
  Type           : Edge, couple of vertex identifiers
  Allowed values : Any couple of vertex identifiers already 
                   defined. Edge should have been defined.
  SIDE (optional)
  Description    : Indicates the orientation side of the arrow.
  Type           : Side type.
  Allowed values : One value in {left, right}.
  Default value  : right.