Plet/Pget are used to share data between patterns inside of a Plambda
Plet defines a variable containing a pattern or data for sharing within the scope of a Plambda.
Using the Pget class, the contents of this variable can then be accessed by key in other patterns within the Plambda.
The name of the variable
The contents of the variable
If return is nil, the pattern will be returned. If not nil, the contents of the return argument will be returned while the variable defined by the Plet will be set to the value of pattern