diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -0,0 +1,8 @@
+# Changelog
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+
+## [0.2.0.0] - 2020-04-19
+### Added
+- fold function to reduce a query result
diff --git a/ejdb2-binding.cabal b/ejdb2-binding.cabal
--- a/ejdb2-binding.cabal
+++ b/ejdb2-binding.cabal
@@ -3,7 +3,7 @@
 category:            Database
 description:         Binding to EJDB2 C library, an embedded JSON noSQL database. Package requires libejdb2 to build. Please see the README on GitHub at <https://github.com/cescobaz/ejdb2haskell#readme>
 synopsis:            Binding to EJDB2 C library, an embedded JSON noSQL database
-version:             0.1.0.0
+version:             0.2.0.0
 license:             MIT
 license-file:        LICENSE
 homepage:            https://github.com/cescobaz/ejdb2haskell#readme
@@ -69,6 +69,7 @@
                        CollectionTests
                        IndexTests
                        OnlineBackupTests
+                       FoldTests
   build-depends:       base ^>=4.12.0.0
                      , tasty ^>=1.2.3
                      , tasty-hunit ^>=0.10.0.2
diff --git a/src/Database/EJDB2.hs b/src/Database/EJDB2.hs
--- a/src/Database/EJDB2.hs
+++ b/src/Database/EJDB2.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE OverloadedStrings #-}
+
 module Database.EJDB2
     ( init
     , Database
@@ -28,6 +30,7 @@
     , ensureIndex
     , removeIndex
     , onlineBackup
+    , fold
     ) where
 
 import           Control.Exception
@@ -35,6 +38,7 @@
 
 import qualified Data.Aeson                             as Aeson
 import qualified Data.ByteString                        as BS
+import qualified Data.HashMap.Strict                    as Map
 import           Data.IORef
 import           Data.Int
 import           Data.Word
@@ -129,42 +133,68 @@
     \countPtr -> c_ejdb_count ejdb jql countPtr 0 >>= checkRC >> peek countPtr
     >>= \(CIntMax int) -> return int
 
+exec :: EJDBExecVisitor -> Database -> Query -> IO ()
+exec visitor (Database _ ejdb) (Query jql _ _) = do
+    visitor <- mkEJDBExecVisitor visitor
+    let exec = EJDBExec.zero { db = ejdb, q = jql, EJDBExec.visitor = visitor }
+    finally (with exec c_ejdb_exec >>= checkRC) (freeHaskellFunPtr visitor)
+
+-- | Iterate over query result building the result
+fold :: Aeson.FromJSON b
+     => Database
+     -> (a
+         -> (Int64, Maybe b)
+         -> a) -- ^ The second argument is a tuple with the object id and the object
+     -> a -- ^ Initial result
+     -> Query
+     -> IO a
+fold database f i query = newIORef (f, i) >>= \ref ->
+    exec (foldVisitor ref) database query >> snd <$> readIORef ref
+
+foldVisitor :: Aeson.FromJSON b
+            => IORef ((a -> (Int64, Maybe b) -> a), a)
+            -> EJDBExecVisitor
+foldVisitor ref _ docPtr _ = do
+    doc <- peek docPtr
+    value <- decode (raw doc)
+    let id = fromIntegral $ EJDBDoc.id doc
+    modifyIORef' ref $ \(f, partial) -> (f, f partial (id, value))
+    return 0
+
 {-|
   Executes a given query and builds a query result as list of tuple with id and document.
 -}
 getList :: Aeson.FromJSON a => Database -> Query -> IO [(Int64, Maybe a)]
-getList = exec Database.EJDB2.visitor
+getList database query = reverse <$> fold database foldList [] query
 
-visitor :: Aeson.FromJSON a => IORef [(Int64, Maybe a)] -> EJDBExecVisitor
-visitor ref _ docPtr _ = do
-    doc <- peek docPtr
-    value <- decode (raw doc)
-    modifyIORef' ref $ \list -> (fromIntegral $ EJDBDoc.id doc, value) : list
-    return 0
+foldList :: Aeson.FromJSON a
+         => [(Int64, Maybe a)]
+         -> (Int64, Maybe a)
+         -> [(Int64, Maybe a)]
+foldList = flip (:)
 
 {-|
   Executes a given query and builds a query result as list of documents with id injected as attribute.
 -}
 getList' :: Aeson.FromJSON a => Database -> Query -> IO [Maybe a]
-getList' = exec Database.EJDB2.visitor'
+getList' database query = reverse <$> fold database foldList' [] query
 
-visitor' :: Aeson.FromJSON a => IORef [Maybe a] -> EJDBExecVisitor
-visitor' ref _ docPtr _ = do
-    doc <- peek docPtr
-    value <- decode' (raw doc) (fromIntegral $ EJDBDoc.id doc)
-    modifyIORef' ref $ \list -> value : list
-    return 0
+foldList'
+    :: Aeson.FromJSON a => [Maybe a] -> (Int64, Maybe Aeson.Value) -> [Maybe a]
+foldList' list (id, value) = parse (setId id value) : list
 
-exec :: (IORef [a] -> EJDBExecVisitor) -> Database -> Query -> IO [a]
-exec visitor (Database _ ejdb) (Query jql _ _) = do
-    ref <- newIORef []
-    visitor <- mkEJDBExecVisitor (visitor ref)
-    let exec = EJDBExec.zero { db = ejdb, q = jql, EJDBExec.visitor = visitor }
-    finally (with exec $ \execPtr -> do
-                 c_ejdb_exec execPtr >>= checkRC
-                 reverse <$> readIORef ref)
-            (freeHaskellFunPtr visitor)
+parse :: Aeson.FromJSON a => Maybe Aeson.Value -> Maybe a
+parse Nothing = Nothing
+parse (Just value) = case Aeson.fromJSON value of
+    Aeson.Success v -> Just v
+    Aeson.Error _ -> Nothing
 
+setId :: Int64 -> Maybe Aeson.Value -> Maybe Aeson.Value
+setId id (Just (Aeson.Object map)) =
+    Just (Aeson.Object (Map.insert "id" (Aeson.Number $ fromIntegral id) map))
+setId _ Nothing = Nothing
+setId _ value = value
+
 {-|
   Save new document into collection under new generated identifier.
 -}
@@ -321,3 +351,4 @@
 onlineBackup (Database _ ejdb) filePath = withCString filePath $ \cFilePath ->
     alloca $ \timestampPtr -> c_ejdb_online_backup ejdb timestampPtr cFilePath
     >>= checkRC >> peek timestampPtr >>= \(CUIntMax t) -> return t
+
diff --git a/src/Database/EJDB2/JBL.hs b/src/Database/EJDB2/JBL.hs
--- a/src/Database/EJDB2/JBL.hs
+++ b/src/Database/EJDB2/JBL.hs
@@ -1,13 +1,10 @@
-{-# LANGUAGE OverloadedStrings #-}
-
-module Database.EJDB2.JBL ( decode, decode', encode, encodeToByteString ) where
+module Database.EJDB2.JBL ( decode, encode, encodeToByteString ) where
 
 import           Control.Exception
 
 import qualified Data.Aeson                  as Aeson
 import qualified Data.ByteString             as BS
 import qualified Data.ByteString.Lazy        as BSL
-import qualified Data.HashMap.Strict         as Map
 import           Data.IORef
 import           Data.Int
 
@@ -21,9 +18,6 @@
 decode :: Aeson.FromJSON a => JBL -> IO (Maybe a)
 decode jbl = Aeson.decode <$> decodeToByteString jbl
 
-decode' :: Aeson.FromJSON a => JBL -> Int64 -> IO (Maybe a)
-decode' jbl id = parse . setId id <$> decode jbl
-
 decodeToByteString :: JBL -> IO BSL.ByteString
 decodeToByteString jbl = do
     ref <- newIORef BSL.empty
@@ -31,18 +25,6 @@
     c_jbl_as_json jbl thePrinter nullPtr 0
         >>= Result.checkRCFinally (freeHaskellFunPtr thePrinter)
     BSL.reverse <$> readIORef ref
-
-parse :: Aeson.FromJSON a => Maybe Aeson.Value -> Maybe a
-parse Nothing = Nothing
-parse (Just value) = case Aeson.fromJSON value of
-    Aeson.Success v -> Just v
-    Aeson.Error _ -> Nothing
-
-setId :: Int64 -> Maybe Aeson.Value -> Maybe Aeson.Value
-setId id (Just (Aeson.Object map)) =
-    Just (Aeson.Object (Map.insert "id" (Aeson.Number $ fromIntegral id) map))
-setId _ Nothing = Nothing
-setId _ value = value
 
 printer :: IORef BSL.ByteString -> JBLJSONPrinter
 printer ref _ 0 (CChar ch) _ _ = do
diff --git a/test/FoldTests.hs b/test/FoldTests.hs
new file mode 100644
--- /dev/null
+++ b/test/FoldTests.hs
@@ -0,0 +1,38 @@
+module FoldTests where
+
+import           Data.Int
+
+import qualified Database.EJDB2         as DB
+import           Database.EJDB2.Options
+import qualified Database.EJDB2.Query   as Query
+
+import           Plant
+
+import           Prelude                hiding ( id )
+
+import           Test.Tasty
+import           Test.Tasty.HUnit
+
+tests :: TestTree
+tests = withResource (DB.open testReadOnlyDatabaseOpts) DB.close $
+    \databaseIO -> testGroup "get" [ foldOnIsTreeTest databaseIO ]
+
+testReadOnlyDatabaseOpts :: Options
+testReadOnlyDatabaseOpts =
+    DB.minimalOptions "./test/read-only-db" [ DB.readonlyOpenFlags ]
+
+foldOnIsTreeTest :: IO DB.Database -> TestTree
+foldOnIsTreeTest databaseIO = testCase "foldOnIsTree" $ do
+    database <- databaseIO
+    query <- Query.fromString "@plants/*"
+    result <- DB.fold database foldOnIsTree (0, 0) query
+    result @?= (1, 3)
+
+foldOnIsTree :: (Int, Int) -> (Int64, Maybe Plant) -> (Int, Int)
+foldOnIsTree acc (_, Nothing) = acc
+foldOnIsTree acc@(trueCount, falseCount) (_, Just plant) =
+    maybe acc
+          (\flag -> if flag
+                    then (trueCount + 1, falseCount)
+                    else (trueCount, falseCount + 1))
+          (isTree plant)
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -6,6 +6,8 @@
 
 import           DeleteTests
 
+import           FoldTests
+
 import           GetTests
 
 import           IndexTests
@@ -32,4 +34,5 @@
                   , CollectionTests.tests
                   , IndexTests.tests
                   , OnlineBackupTests.tests
+                  , FoldTests.tests
                   ]