From d0af1024d008113347183024df41c739d7644c02 Mon Sep 17 00:00:00 2001
From: Nick McAvoy <nicholas.mcavoy@gmail.com>
Date: Tue, 16 Sep 2014 22:20:11 -0400
Subject: matchMetadata for examining metadata when defining rules

---
 src/Hakyll/Core/Rules.hs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'src/Hakyll')

diff --git a/src/Hakyll/Core/Rules.hs b/src/Hakyll/Core/Rules.hs
index c248a9b..1c8b93c 100644
--- a/src/Hakyll/Core/Rules.hs
+++ b/src/Hakyll/Core/Rules.hs
@@ -19,6 +19,7 @@
 module Hakyll.Core.Rules
     ( Rules
     , match
+    , matchMetadata
     , create
     , version
     , compile
@@ -131,6 +132,19 @@ match pattern rules = do
     setMatches ids env = env {rulesMatches = ids}
 
 
+--------------------------------------------------------------------------------
+matchMetadata :: Pattern -> (Metadata -> Bool) -> Rules () -> Rules ()
+matchMetadata pattern metadataPred rules = do
+    tellPattern pattern
+    flush
+    idsAndMetadata <- getAllMetadata pattern
+    let ids = map fst . filter (metadataPred . snd) $ idsAndMetadata
+    tellResources ids
+    Rules $ local (setMatches ids) $ unRules $ rules >> flush
+  where
+    setMatches ids env = env {rulesMatches = ids}
+
+
 --------------------------------------------------------------------------------
 create :: [Identifier] -> Rules () -> Rules ()
 create ids rules = do
-- 
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