This is a grasshopper recreation of a design pattern 'Jig' found in Robert Woodbury's Elements of Parametric Design. A surface is lofted through a series of profile curves. These curves are controlled by a Jig (crossbow).
A surface is lofted through several profile curves. These curves are all copies of a master profile curve. This master curve is controlled by 4 control points that are determined by the 'crossbow'. The crossbow has two horizontal lines and a vertical line - this comprises the jig that controls the curve and in effect, the resultant surface.
The definition is structure into 3 parts: 1) the crossbow and master curve, 2) a reference curve which provides frames on which the master curve will be placed and 3) the lofted surface. Take note that we begin building the crossbow/master curve with a plane component. This allows us to use a 'orient' component later on to place copies of the master profile onto frames(planes) along the reference curve. In order to construct the crossbow, we exploit its bilateral symmetry and use 'mirror curve' components.
The grasshopper definitions can be downloaded here.