X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FArray%2FST.hs;h=828ae63ffa6d4b3e2a955e1098746a38ab0adbb1;hb=74bc2d04fdbae494bcf4839c4ec5e6ec1d0bf600;hp=cd81d8309c82739d2c2b4b506cf708dbb9ab3094;hpb=c54cf4e02e743cc50dd403812bd7a31ff5f583bc;p=haskell-directory.git

diff --git a/Data/Array/ST.hs b/Data/Array/ST.hs
index cd81d83..828ae63 100644
--- a/Data/Array/ST.hs
+++ b/Data/Array/ST.hs
@@ -6,9 +6,9 @@
 -- 
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
--- Portability :  non-portable
+-- Portability :  non-portable (uses Data.Array.MArray)
 --
--- Mutable boxed and unboxed arrays in the 'ST' monad.
+-- Mutable boxed and unboxed arrays in the 'Control.Monad.ST.ST' monad.
 --
 -----------------------------------------------------------------------------
 
@@ -16,12 +16,12 @@ module Data.Array.ST (
 
    -- * Boxed arrays
    STArray,		-- instance of: Eq, MArray
+   runSTArray,
 
-#ifdef __GLASGOW_HASKELL__
    -- * Unboxed arrays
    STUArray,		-- instance of: Eq, MArray
+   runSTUArray,
    castSTUArray,	-- :: STUArray s i a -> ST s (STUArray s i b)
-#endif
 
    -- * Overloaded mutable array interface
    module Data.Array.MArray,
@@ -30,19 +30,48 @@ module Data.Array.ST (
 import Prelude
 
 import Data.Array.MArray
+import Data.Array.Base	( STUArray, castSTUArray, UArray, unsafeFreezeSTUArray )
+import Control.Monad.ST	( ST, runST )
+
 #ifdef __HUGS__
-import Hugs.ST
-#else
-import Data.Array.Base	hiding (MArray(..))
+import Hugs.Array	( Array )
+import Hugs.ST		( STArray, unsafeFreezeSTArray )
 #endif
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.Arr
-import GHC.ST
-
--- | Casts an 'STUArray' with one element type into one with a
--- different element type.  All the elements of the resulting array
--- are undefined (unless you know what you\'re doing...).
-castSTUArray :: STUArray s ix a -> ST s (STUArray s ix b)
-castSTUArray (STUArray l u marr#) = return (STUArray l u marr#)
+import GHC.Arr		( STArray, Array, unsafeFreezeSTArray )
 #endif
+
+-- | A safe way to create and work with a mutable array before returning an
+-- immutable array for later perusal.  This function avoids copying
+-- the array before returning it - it uses 'unsafeFreeze' internally, but
+-- this wrapper is a safe interface to that function.
+--
+runSTArray :: (Ix i)
+	   => (forall s . ST s (STArray s i e))
+	   -> Array i e
+runSTArray st = runST (st >>= unsafeFreezeSTArray)
+
+-- | A safe way to create and work with an unboxed mutable array before
+-- returning an immutable array for later perusal.  This function
+-- avoids copying the array before returning it - it uses
+-- 'unsafeFreeze' internally, but this wrapper is a safe interface to
+-- that function.
+--
+runSTUArray :: (Ix i)
+	   => (forall s . ST s (STUArray s i e))
+	   -> UArray i e
+runSTUArray st = runST (st >>= unsafeFreezeSTUArray)
+
+
+-- INTERESTING... this is the type we'd like to give to runSTUArray:
+--
+-- runSTUArray :: (Ix i, IArray UArray e, 
+--	        forall s. MArray (STUArray s) e (ST s))
+-- 	   => (forall s . ST s (STUArray s i e))
+--	   -> UArray i e
+--
+-- Note the quantified constraint.  We dodged the problem by using
+-- unsafeFreezeSTUArray directly in the defn of runSTUArray above, but
+-- this essentially constrains us to a single unsafeFreeze for all STUArrays
+-- (in theory we might have a different one for certain element types).