Feat is a library that offers support for counting, enumerating, and sampling
objects of a certain kind, such as (say) the inhabitants of an algebraic data
type.

Feat was inspired by the paper
Feat: Functional Enumeration of Algebraic Types
by Jonas Duregård, Patrik Jansson and Meng Wang (2012).
It can perhaps be compared with the Haskell library
testing-feat,
although a detailed comparison has not been carried out.

The library is laid out as follows:

• The module Feat.IFSeq implements
  the signature Feat.IFSEQ
  of (implicit, finite) sequences.

  These sequences are implicit, which means that they are not explicitly
  epresented in memory as an actual sequence of elements; instead, they are
  described by a data structure which contains enough information to
  produce an arbitrary element upon request. This design decision imposes
  some constraints on the operations that can be efficiently supported; for
  instance, filter is not supported.

• The module Feat.Enum implements
  enumerations.
  An enumeration of type 'a enum is a function of a size s
  to a sequence of elements of size s.

• The module Feat.Bigint
  offers a function random of type Z.t -> Z.t,
  thus repairing an unfortunate omission in the library zarith.

• The external library
  Fix
  comes in handy when building enumerations
  of recursive algebraic data types:
  see the demo.