[commit: base] master: Declare a family for subtraction. (5334361)

[Iavor Diatchki]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/base

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/533436192c78b7d2352c9d3f5689c4f24dc0920f

>---------------------------------------------------------------

commit 533436192c78b7d2352c9d3f5689c4f24dc0920f
Author: Iavor S. Diatchki <iavor.diatchki at gmail.com>
Date:   Sun Nov 11 18:23:47 2012 -0800

    Declare a family for subtraction.

>---------------------------------------------------------------

 GHC/TypeLits.hs |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/GHC/TypeLits.hs b/GHC/TypeLits.hs
index 4db4cbb..b8733ca 100644
--- a/GHC/TypeLits.hs
+++ b/GHC/TypeLits.hs
@@ -27,6 +27,7 @@ module GHC.TypeLits
 
     -- * Functions on type nats
   , type (<=), type (<=?), type (+), type (*), type (^)
+  , type (-)
 
     -- * Destructing type-nat singletons.
   , isZero, IsZero(..)
@@ -106,6 +107,10 @@ type family (m :: Nat) * (n :: Nat) :: Nat
 -- | Exponentiation of type-level naturals.
 type family (m :: Nat) ^ (n :: Nat) :: Nat
 
+-- | Subtraction of type-level naturals.
+-- Note that this operation is unspecified for some inputs.
+type family (m :: Nat) - (n :: Nat) :: Nat
+
 
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