diff options
Diffstat (limited to 'haddock-api/src/Haddock/Syb.hs')
| -rw-r--r-- | haddock-api/src/Haddock/Syb.hs | 16 |
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. |