From a307e39d47eae349ced1358c85dfa592a76983ec Mon Sep 17 00:00:00 2001
From: Neil Brown <neil@twistedsquare.com>
Date: Thu, 2 Apr 2009 15:07:17 +0000
Subject: [PATCH] Added a Read instance for Meta (taken from my benchmarks for
 the ICFP paper)

---
 data/Metadata.hs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/data/Metadata.hs b/data/Metadata.hs
index 597921e..76a46fa 100644
--- a/data/Metadata.hs
+++ b/data/Metadata.hs
@@ -22,6 +22,7 @@ module Metadata where
 {-! global : Haskell2Xml !-}
 
 import Data.Generics
+import Data.List
 import Numeric
 import Text.Printf
 import Text.Regex
@@ -46,6 +47,20 @@ instance Show Meta where
         Just s -> s ++ ":" ++ show (metaLine m) ++ ":" ++ show (metaColumn m)
         Nothing -> "no source position"
 
+dropSpaces :: String -> String
+dropSpaces = dropWhile (== ' ')
+
+instance Read Meta where
+  readsPrec n str
+    | show emptyMeta `isPrefixOf` dropSpaces str
+       = [(Meta Nothing 0 0, drop (length $ show emptyMeta) $ dropSpaces str)]
+    | otherwise
+       = [ (Meta (Just fn) (read l) (read n), r'') ]
+       where
+         (fn, ':':r) = span (/= ':') $ dropSpaces str
+         (l, ':':r') = span (/= ':') r
+         (n, r'') = span (`elem` ['0'..'9']) r'
+
 -- | Encode a Meta as the prefix of a string.
 packMeta :: Meta -> String -> String
 packMeta m s