Only-0.1: The 1-tuple type or single-value "collection"

This package provides a canonical anonymous 1-tuple type missing from Haskell for attaching typeclass instances.

NOTE: There is also the OneTuple package which by using a boxed data-type provides a 1-tuple type which has laziness properties which are more faithful to the ones of Haskell's native tuples; whereas the primary purpose of Only is to provide the traditionally so named type-wrapper for attaching typeclass instances.