Haskell's canonical list of tuples syntax for defining maps is not very
 convenient and also has ambiguous semantics. This package leverages do
 notation to create a lighter syntax that makes semantics explicit and also
 allows the option of fail-fast handling of duplicate keys.
 .
 This package provides a library for the Haskell programming language.
 See http://www.haskell.org/ for more information on Haskell.