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.
