New justList function.

src/Database/Esqueleto.hs

@@ -48,7 +48,7 @@ module Database.Esqueleto
              , min_, max_, sum_, avg_, castNum, castNumM
              , coalesce, coalesceDefault
              , lower_, like, ilike, (%), concat_, (++.)
-             , subList_select, subList_selectDistinct, valList
+             , subList_select, subList_selectDistinct, valList, justList
              , in_, notIn, exists, notExists
              , set, (=.), (+=.), (-=.), (*=.), (/=.)
              , case_ )

src/Database/Esqueleto/Internal/Language.hs

@@ -427,6 +427,13 @@ class (Functor query, Applicative query, Monad query) =>
   -- | Lift a list of constant value from Haskell-land to the query.
   valList :: PersistField typ => [typ] -> expr (ValueList typ)
 
+  -- | Same as 'just' but for 'ValueList'.  Most of the time you
+  -- won't need it, though, because you can use 'just' from
+  -- inside 'subList_select' or 'Just' from inside 'valList'.
+  --
+  -- /Since: 2.2.12/
+  justList :: expr (ValueList typ) -> expr (ValueList (Maybe typ))
+
   -- | @IN@ operator.
   in_ :: PersistField typ => expr (Value typ) -> expr (ValueList typ) -> expr (Value Bool)
 

src/Database/Esqueleto/Internal/Sql.hs

@@ -496,6 +496,9 @@ instance Esqueleto SqlQuery SqlExpr SqlBackend where
   valList vals = EList $ ERaw Parens $ const ( uncommas ("?" <$ vals)
                                              , map toPersistValue vals )
 
+  justList EEmptyList = EEmptyList
+  justList (EList v)  = EList (just v)
+
   v `in_`   e = ifNotEmptyList e False $ unsafeSqlBinOp     " IN " v (veryUnsafeCoerceSqlExprValueList e)
   v `notIn` e = ifNotEmptyList e True  $ unsafeSqlBinOp " NOT IN " v (veryUnsafeCoerceSqlExprValueList e)