Open algebraic data types.
This library, built upon row-types, provides types and functions for variants of various functors that all have the same type applied to them. This is very similar to, and inspired by, haskus-utils-variant. At the time of writing, the compile-time performance of haskus-utils-variant is poor for variants with many fields, which should be improved in this package by using row-types.
The main types of interest in this package are VarF and OpenADT. VarF wraps a variant of functors, all over the same type, and provides a functor instance that fmaps over whatever the variant is. OpenADT is the fixed-point type of VarF, which allows for recursive structures to be created.
A convenience function, mkVarPattern from Data.OpenADT.TH, generates patterns that can be used as constructors for variants. The key aspect of these patterns is that they are polymorphic in the type of the row, allowing them to be used as constructors for any open algebraic data type that includes a particular constructor.
For examples, see the Data.OpenADT.Tutorial module.