[commit: ghc] master: Improve docs for -XNegativeLiterals (33c880b)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/33c880b43ed72d77f6b1d95d5ccefbd376c78c78/ghc

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

commit 33c880b43ed72d77f6b1d95d5ccefbd376c78c78
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Thu Aug 29 13:01:16 2013 +0100

    Improve docs for -XNegativeLiterals


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33c880b43ed72d77f6b1d95d5ccefbd376c78c78
 docs/users_guide/glasgow_exts.xml |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 7a1af04..6c4046e 100644
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -446,13 +446,18 @@ Indeed, the bindings can even be recursive.
           The literal <literal>-123</literal> is, according to
           Haskell98 and Haskell 2010, desugared as
           <literal>negate (fromInteger 123)</literal>.
-      </para>
-
-      <para>
          The language extension <option>-XNegativeLiterals</option>
          means that it is instead desugared as
          <literal>fromInteger (-123)</literal>. 
       </para>
+
+      <para>
+      This can make a difference when the positive and negative range of 
+      a numeric data type don't match up.  For example, 
+      in 8-bit arithmetic -128 is representable, but +128 is not.
+      So <literal>negate (fromInteger 128)</literal> will elicit an 
+      unexpected integer-literal-overflow message.
+      </para>
    </sect2>
 
     <sect2 id="num-decimals">