added exprHash in the Haskell binding

src/runtime/haskell-bind/PGF2.hsc

@@ -39,6 +39,7 @@ module PGF2 (-- * PGF
              mkFloat,unFloat,
              mkMeta,unMeta,
              mkCId,
+             exprHash,
              treeProbability,
 
              -- ** Types
@@ -323,6 +324,15 @@ treeProbability (PGF p _) (Expr c_expr touch1) =
     touch1
     return (realToFrac res)
 
+exprHash :: Int32 -> Expr -> Int32
+exprHash h (Expr c_expr touch1) =
+  unsafePerformIO $ do
+    h <- pgf_expr_hash (fromIntegral h) c_expr
+    touch1
+    return (fromIntegral h)
+
+    
+
 -----------------------------------------------------------------------------
 -- Graphviz
 

src/runtime/haskell-bind/PGF2/FFI.hs

@@ -328,6 +328,9 @@ foreign import ccall "pgf/expr.h pgf_expr_arity"
 foreign import ccall "pgf/expr.h pgf_expr_eq"
   pgf_expr_eq :: PgfExpr -> PgfExpr -> IO CInt
 
+foreign import ccall "pgf/expr.h pgf_expr_hash"
+  pgf_expr_hash :: Word -> PgfExpr -> IO Word
+
 foreign import ccall "pgf/expr.h pgf_compute_tree_probability"
   pgf_compute_tree_probability :: Ptr PgfPGF -> PgfExpr -> IO CFloat