{-# LANGUAGE RankNTypes, Trustworthy #-}------------------------------------------------------------------------------- |-- Module : Data.Array.ST-- Copyright : (c) The University of Glasgow 2001-- License : BSD-style (see the file libraries/base/LICENSE)---- Maintainer : libraries@haskell.org-- Stability : experimental-- Portability : non-portable (uses Data.Array.MArray)---- Mutable boxed and unboxed arrays in the 'Control.Monad.ST.ST' monad.-------------------------------------------------------------------------------moduleData.Array.ST(-- * Boxed arraysSTArray,-- instance of: Eq, MArrayrunSTArray ,-- * Unboxed arraysSTUArray ,-- instance of: Eq, MArrayrunSTUArray ,-- * Overloaded mutable array interfacemoduleData.Array.MArray ,)whereimportData.Array.Base (STUArray ,UArray ,unsafeFreezeSTUArray )importData.Array.MArray importControl.Monad.ST(ST,runST)importGHC.Arr(STArray,Array,unsafeFreezeSTArray)-- | 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 ::(foralls .STs (STArrays i e ))->Arrayi e runSTArray :: forall i e. (forall s. ST s (STArray s i e)) -> Array i e
runSTArray forall s. ST s (STArray s i e)
st =(forall s. ST s (Array i e)) -> Array i e
forall a. (forall s. ST s a) -> a
runST(ST s (STArray s i e)
forall s. ST s (STArray s i e)
st ST s (STArray s i e)
-> (STArray s i e -> ST s (Array i e)) -> ST s (Array i e)
forall a b. ST s a -> (a -> ST s b) -> ST s b
forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
>>=STArray s i e -> ST s (Array i e)
forall s i e. STArray s i e -> ST s (Array i e)
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 ::(foralls .STs (STUArray s i e ))->UArray i e runSTUArray :: forall i e. (forall s. ST s (STUArray s i e)) -> UArray i e
runSTUArray forall s. ST s (STUArray s i e)
st =(forall s. ST s (UArray i e)) -> UArray i e
forall a. (forall s. ST s a) -> a
runST(ST s (STUArray s i e)
forall s. ST s (STUArray s i e)
st ST s (STUArray s i e)
-> (STUArray s i e -> ST s (UArray i e)) -> ST s (UArray i e)
forall a b. ST s a -> (a -> ST s b) -> ST s b
forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
>>=STUArray s i e -> ST s (UArray i e)
forall s i e. STUArray s i e -> ST s (UArray i e)
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).