major rewrite

[hs-rrdtool.git] / Database / RRDtool / Create.hs

diff --git a/Database/RRDtool/Create.hs b/Database/RRDtool/Create.hs
index cb41c211aa7912d01c6ff04e1a6703c5ca9ad2c1..5438e044d02b5a746256ed95fe3686a75b29028c 100644 (file)
--- a/Database/RRDtool/Create.hs
+++ b/Database/RRDtool/Create.hs
@@ -11,7 +11,7 @@ module Database.RRDtool.Create
 
     -- Database.RRDtool.Expression
     , Constant(..)
-    , IsVarName(..)
+    , IsVarName
     , Variable(..)
     , CommonUnaryOp(..)
     , CommonBinaryOp(..)
@@ -28,6 +28,7 @@ import Data.HList
 import Data.Time.Clock
 import Data.Time.Clock.POSIX
 import Database.RRDtool.Expression
+import Types.Data.Bool
 
 
 -- |A single RRD can accept input from several data sources (DS), for
@@ -152,7 +153,8 @@ data ComputedDataSource e
     }
     deriving (Show, Eq, Ord)
 
-instance IsCommonExpr e => DataSource (ComputedDataSource e)
+instance (IsCommonExpr e ~ True) =>
+    DataSource (ComputedDataSource e)
 
 
 dsTest = ComputedDataSource {