content: {- |
     Module      : Data.Graph.Inductive.Proxy
     Description : Proxy type for graph tests
     Copyright   : (c) Ivan Lazar Miljenovic
     License     : BSD3
     Maintainer  : Ivan.Miljenovic@gmail.com
  
     To avoid relying upon a newer version of base, this defines a
     custom Proxy type and convenience functions.
  
   -}
  module Data.Graph.Inductive.Proxy where
  
  import qualified Data.Graph.Inductive.PatriciaTree as P
  import qualified Data.Graph.Inductive.Tree         as T
  
  import Data.Word (Word8)
  
  -- -----------------------------------------------------------------------------
  
  -- By default, we want to avoid using 'Int' to avoid clashing with the
  -- 'Node' type.  Don't want to use a floating type in case of
  -- potential Eq problems.
  type GraphType gr = gr Char Word8
  
  type GraphProxy gr = Proxy (GraphType gr)
  
  type TreeP = GraphProxy T.Gr
  
  type PatriciaTreeP = GraphProxy P.Gr
  
  -- Not using the Data.Proxy module so this also works with older
  -- versions of GHC.
  
  data Proxy a = Proxy
    deriving (Eq, Ord, Show, Read)
  
  asProxyTypeOf :: a -> Proxy a -> a
  asProxyTypeOf a _ = a
  
  withProxy :: Proxy a -> a -> a
  withProxy _ a = a
  
  asProxyGraphTypeOf :: gr () () -> Proxy (gr a b) -> gr () ()
  asProxyGraphTypeOf gr _ = gr
  