Implement `Natural` number type (re #9818)

This implements a `Natural` type for representing unsigned arbitrary
precision integers.

When available, `integer-gmp>=1.0.0`'s `BigNat` type is used as
building-block to construct `Natural` as an algebraic data-type.
Otherwise, `Natural` falls back being a `newtype`-wrapper around
`Integer` (as is done in Edward Kmett's `nats` package).

The `GHC.Natural` module exposes an internal GHC-specific API, while
`Numeric.Natural` provides the official & portable API.

Reviewed By: austin, ekmett

Differential Revision: https://phabricator.haskell.org/D473

1 files changed, 24 insertions, 0 deletions

diff --git a/libraries/base/Numeric/Natural.hs b/libraries/base/Numeric/Natural.hs
new file mode 100644
index 0000000000..3a96501f1e
--- /dev/null
+++ b/libraries/base/Numeric/Natural.hs
@@ -0,0 +1,24 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE Trustworthy #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Numeric.Natural
+-- Copyright   :  (C) 2014 Herbert Valerio Riedel,
+--                (C) 2011 Edward Kmett
+-- License     :  see libraries/base/LICENSE
+--
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- The arbitrary-precision 'Natural' number type.
+--
+-- /Since: 4.8.0.0/
+-----------------------------------------------------------------------------
+
+module Numeric.Natural
+    ( Natural
+    ) where
+
+import GHC.Natural