Add BackendBuild class.

diagrams-lib.cabal

@@ -33,6 +33,7 @@ Library
                        Diagrams.Attributes,
                        Diagrams.Attributes.Compile,
                        Diagrams.Backend.CmdLine,
+                       Diagrams.Backend.Build,
                        Diagrams.BoundingBox,
                        Diagrams.Combinators,
                        Diagrams.Coordinates,

src/Diagrams/Backend/Build.hs

@@ -0,0 +1,30 @@
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Diagrams.Builder.Class
+-- Copyright   :  (c) 2014 diagrams-lib team (see LICENSE)
+-- License     :  BSD-style (see LICENSE)
+-- Maintainer  :  [email protected]
+--
+-- General class for building diagrams to files.
+--
+-----------------------------------------------------------------------------
+module Diagrams.Backend.Build where
+
+import Diagrams.Core
+import Diagrams.Size
+import Data.Monoid (Any)
+import Linear.V2
+import Control.Lens (Lens')
+
+-- | Generic class for building diagrams whose output is a file with a
+--   2D size.
+class Backend b v n => BackendBuild b v n where
+  -- | Lens onto the size of the output file.
+  outputSize :: Lens' (Options b v n) (SizeSpec V2 n)
+
+  -- | Build a diagram of the given format to the path using the
+  --   backend's options. The @Maybe String@ returns any errors.
+  saveDia :: FilePath -> Options b v n -> QDiagram b v n Any -> IO ()
+