change Measure parameter to vector rather than scalar type

This lets us properly express vector-space-generic V and Transformable
instances for Measure.

src/Diagrams/Core/Compile.hs

@@ -132,7 +132,7 @@ fromDTree = fromDTree' mempty
 --   transformation used to convert the diagram from local to output
 --   units.
 toRTree
-  :: (HasLinearMap v, InnerSpace v, Data (Scalar v), OrderedField (Scalar v), Monoid m, Semigroup m)
+  :: (HasLinearMap v, InnerSpace v, Data v, Data (Scalar v), OrderedField (Scalar v), Monoid m, Semigroup m)
   => Transformation v -> QDiagram b v m -> RTree b v Annotation
 toRTree globalToOutput d
   = (fmap . onRStyle) (toOutput gToO nToO)
@@ -162,11 +162,11 @@ onRStyle _ n          = n
 --   case if all transformations have been fully pushed down and
 --   applied).
 toOutput
-  :: forall v. (Data (Scalar v), Num (Scalar v))
+  :: forall v. (Data v, Data (Scalar v), Num (Scalar v))
   => Scalar v -> Scalar v -> Style v -> Style v
 toOutput globalToOutput normToOutput = gmapAttrs convert
   where
-    convert :: Measure (Scalar v) -> Measure (Scalar v)
+    convert :: Measure v -> Measure v
     convert m@(Output _)   = m
     convert (Local s)      = Output s
     convert (Global s)     = Output (globalToOutput * s)

src/Diagrams/Core/Types.hs

@@ -8,6 +8,7 @@
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses      #-}
 {-# LANGUAGE ScopedTypeVariables        #-}
+{-# LANGUAGE StandaloneDeriving         #-}
 {-# LANGUAGE TupleSections              #-}
 {-# LANGUAGE TypeFamilies               #-}
 {-# LANGUAGE TypeOperators              #-}
@@ -166,11 +167,22 @@ import           Diagrams.Core.V
 --  Measurement Units  -------------------------------------
 ------------------------------------------------------------
 -- | Type of measurement units for attributes.
-data Measure t = Output t
-               | Normalized t
-               | Local t
-               | Global t
-  deriving (Eq, Ord, Show, Data, Typeable)
+data Measure v = Output (Scalar v)
+               | Normalized (Scalar v)
+               | Local (Scalar v)
+               | Global (Scalar v)
+  deriving (Typeable)
+
+deriving instance (Eq (Scalar v)) => Eq (Measure v)
+deriving instance (Ord (Scalar v)) => Ord (Measure v)
+deriving instance (Show (Scalar v)) => Show (Measure v)
+deriving instance (Typeable v, Data v, Data (Scalar v)) => Data (Measure v)
+
+type instance V (Measure v) = v
+
+instance (HasLinearMap v, Floating (Scalar v)) => Transformable (Measure v) where
+  transform tr (Local x) = Local (avgScale tr * x)
+  transform _ y = y
 
 ------------------------------------------------------------
 --  Diagrams  ----------------------------------------------