Ben Gamari authored Dec 18, 2015 and Ben Gamari committed Dec 18, 2015

This type is occurs very often but previously had multiple, meaning it
could not be unboxed. Even worse, these constructors didn't offer any
compelling safety benefits. Thankfully, the type is abstract, so
changing the representation to be a single-constructor type was quite
straightforward.

Reviewers: austin

Subscribers: alanz, thomie, hvr

Differential Revision: https://phabricator.haskell.org/D1657