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authorƁukasz Hanuszczak <lukasz.hanuszczak@gmail.com>2015-07-19 18:16:11 +0200
committerMateusz Kowalczyk <fuuzetsu@fuuzetsu.co.uk>2015-08-21 18:22:30 +0100
commitd5700e1427f7171db0e0e9393aedb734b554459f (patch)
treedf24abb0667948cfb831227d00653682d4a32976 /haddock-api
parent2c94f5a7804ecf84f818a64ba41ca5829621323c (diff)
Add SYB-like utility function for performing stateful queries.
Diffstat (limited to 'haddock-api')
-rw-r--r--haddock-api/src/Haddock/Syb.hs16
1 files changed, 15 insertions, 1 deletions
diff --git a/haddock-api/src/Haddock/Syb.hs b/haddock-api/src/Haddock/Syb.hs
index 2016b74c..4847e486 100644
--- a/haddock-api/src/Haddock/Syb.hs
+++ b/haddock-api/src/Haddock/Syb.hs
@@ -2,7 +2,7 @@
module Haddock.Syb
- ( everything, everywhere
+ ( everything, everythingWithState, everywhere
, mkT
, combine
) where
@@ -20,6 +20,20 @@ everything :: (r -> r -> r) -> (forall a. Data a => a -> r)
-> (forall a. Data a => a -> r)
everything k f x = foldl k (f x) (gmapQ (everything k f) x)
+
+-- | Perform a query with state on each level of a tree.
+--
+-- This is the same as 'everything' but allows for stateful computations. In
+-- SYB it is called @everythingWithContext@ but I find this name somewhat
+-- nicer.
+everythingWithState :: s -> (r -> r -> r)
+ -> (forall a. Data a => a -> s -> (r, s))
+ -> (forall a. Data a => a -> r)
+everythingWithState s k f x =
+ let (r, s') = f x s
+ in foldl k r (gmapQ (everythingWithState s' k f) x)
+
+
-- | Apply transformation on each level of a tree.
--
-- Just like 'everything', this is stolen from SYB package.