make use of hString

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

diff --git a/Database/RRDtool/Expression.hs b/Database/RRDtool/Expression.hs
index f2d2574f93b8a23d70ed0c0e0b05004ffbacd1c5..5c44213e47fb2fa4649b82c489e5d543cc3af79d 100644 (file)
--- a/Database/RRDtool/Expression.hs
+++ b/Database/RRDtool/Expression.hs
@@ -2,6 +2,7 @@
   EmptyDataDecls,
   FlexibleInstances,
   TypeFamilies,
+  TypeOperators,
   MultiParamTypeClasses,
   UndecidableInstances
   #-}
@@ -14,6 +15,7 @@ module Database.RRDtool.Expression
     , IsIterativeExpr
 
     , IsVarName
+    , hString
 
     , Constant(..)
     , Variable(..)
@@ -32,6 +34,7 @@ module Database.RRDtool.Expression
     where
 
 import Data.HList
+import Data.HList.String
 import Types.Data.Bool
 import Types.Data.Num hiding ((:*:))
 import Types.Data.Ord
@@ -75,13 +78,13 @@ type instance IsIterativeExpr Constant = True
 type instance MentionedVars   Constant = HNil
 
 {- This is what we want to do but GHC can't handle this for now. 
-class ( (HLengthOf str :<=: D255) ~ True
+class ( (HLengthOf str :<=: D19) ~ True
       , HString str
       )
     => IsVarName str
 -}
 type family   IsVarName str
-type instance IsVarName str = ( (HLength str :<=: D255)
+type instance IsVarName str = ( (HLength str :<=: D19)
                                 :&&:
                                 (HAll IsGoodLetterForVarNameA str)
                               )