  We describe Haskell implementations of interesting combinatorial generation
algorithms with focus on boolean functions and logic circuit representations.
  First, a complete exact combinational logic circuit synthesizer is described
as a combination of catamorphisms and anamorphisms.
  Using pairing and unpairing functions on natural number representations of
truth tables, we derive an encoding for Binary Decision Diagrams (BDDs) with
the unique property that its boolean evaluation faithfully mimics its
structural conversion to a a natural number through recursive application of a
matching pairing function.
  We then use this result to derive ranking and unranking functions for BDDs
and reduced BDDs.
  Finally, a generalization of the encoding techniques to Multi-Terminal BDDs
is provided.
  The paper is organized as a self-contained literate Haskell program,
available at http://logic.csci.unt.edu/tarau/research/2008/fBDD.zip .
  Keywords: exact combinational logic synthesis, binary decision diagrams,
encodings of boolean functions, pairing/unpairing functions, ranking/unranking
functions for BDDs and MTBDDs, declarative combinatorics in Haskell
