[commit: ghc] wip/custom-type-errors: Add Haddoc documentation. (3ba1639)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/custom-type-errors
Link       : http://ghc.haskell.org/trac/ghc/changeset/3ba1639da54b5cac5c65d0c75f9284a9acdcd9ae/ghc

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

commit 3ba1639da54b5cac5c65d0c75f9284a9acdcd9ae
Author: Iavor S. Diatchki <diatchki at galois.com>
Date:   Thu Oct 29 13:54:40 2015 -0700

    Add Haddoc documentation.


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

3ba1639da54b5cac5c65d0c75f9284a9acdcd9ae
 libraries/base/GHC/TypeLits.hs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/libraries/base/GHC/TypeLits.hs b/libraries/base/GHC/TypeLits.hs
index 7b94785..f124017 100644
--- a/libraries/base/GHC/TypeLits.hs
+++ b/libraries/base/GHC/TypeLits.hs
@@ -196,10 +196,22 @@ type family (m :: Nat) ^ (n :: Nat) :: Nat
 type family (m :: Nat) - (n :: Nat) :: Nat
 
 
+-- | A description of a custom type error.
 data {-kind-} ErrorMessage = Text Symbol
+                             -- ^ Show the text as is.
+
                            | forall t. ShowType t
+                             -- ^ Pretty print the type.
+                             -- @ShowType :: k -> ErrorMessage@
+
                            | ErrorMessage :<>: ErrorMessage
+                             -- ^ Put two pieces of error message next
+                             -- to each other.
+
                            | ErrorMessage :$$: ErrorMessage
+                             -- ^ Stack two pieces of error message on top
+                             -- of each other.
+
 infixl 5 :$$:
 infixl 6 :<>: