loop

rel8.cabal

@@ -111,6 +111,7 @@ library
     Rel8.Query.Indexed
     Rel8.Query.Limit
     Rel8.Query.List
+    Rel8.Query.Loop
     Rel8.Query.Maybe
     Rel8.Query.Null
     Rel8.Query.Opaleye

src/Rel8.hs

@@ -245,6 +245,9 @@ module Rel8
   , without
   , withoutBy
 
+    -- ** @WITH RECURSIVE@
+  , loop
+
     -- ** Aggregation
   , Aggregate
   , Aggregates
@@ -359,6 +362,7 @@ import Rel8.Query.Filter
 import Rel8.Query.Indexed
 import Rel8.Query.Limit
 import Rel8.Query.List
+import Rel8.Query.Loop
 import Rel8.Query.Maybe
 import Rel8.Query.Null
 import Rel8.Query.Order

src/Rel8/Query/Loop.hs

@@ -0,0 +1,27 @@
+{-# language FlexibleContexts #-}
+
+module Rel8.Query.Loop
+  ( loop
+  ) where
+
+-- base
+import Prelude
+
+-- opaleye
+import Opaleye.Lateral ( lateral )
+import Opaleye.WithRecursive ( withRecursiveExplicit )
+
+-- rel8
+import Rel8.Expr ( Expr )
+import Rel8.Query ( Query )
+import Rel8.Query.Opaleye ( fromOpaleye, toOpaleye )
+import Rel8.Table ( Table )
+import Rel8.Table.Opaleye ( binaryspec )
+
+
+loop :: Table Expr a => Query a -> (a -> Query a) -> Query a
+loop base recurse =
+  fromOpaleye $ withRecursiveExplicit binaryspec base' recurse'
+  where
+    base' = toOpaleye base
+    recurse' = lateral $ toOpaleye . recurse