2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[module_ST]{The State Transformer Monad, @ST@}
7 {-# OPTIONS -fno-implicit-prelude #-}
11 import IOBase ( error ) -- [Source not needed]
14 import PrelBase ( Int, Bool, ($), ()(..) )
15 import GHC ( newArray#, readArray#, writeArray#, sameMutableArray# )
18 %*********************************************************
20 \subsection{Variables}
22 %*********************************************************
25 type MutableVar s a = MutableArray s Int a
27 newVar :: a -> ST s (MutableVar s a)
28 readVar :: MutableVar s a -> ST s a
29 writeVar :: MutableVar s a -> a -> ST s ()
30 sameVar :: MutableVar s a -> MutableVar s a -> Bool
32 newVar init = ST $ \ (S# s#) ->
33 case (newArray# 1# init s#) of { StateAndMutableArray# s2# arr# ->
34 (MutableArray vAR_IXS arr#, S# s2#) }
36 vAR_IXS = error "newVar: Shouldn't access `bounds' of a MutableVar\n"
38 readVar (MutableArray _ var#) = ST $ \ (S# s#) ->
39 case readArray# var# 0# s# of { StateAndPtr# s2# r ->
42 writeVar (MutableArray _ var#) val = ST $ \ (S# s#) ->
43 case writeArray# var# 0# val s# of { s2# ->
46 sameVar (MutableArray _ var1#) (MutableArray _ var2#)
47 = sameMutableArray# var1# var2#
52 sameMutableArray :: MutableArray s ix elt -> MutableArray s ix elt -> Bool
53 sameMutableByteArray :: MutableByteArray s ix -> MutableByteArray s ix -> Bool
55 sameMutableArray (MutableArray _ arr1#) (MutableArray _ arr2#)
56 = sameMutableArray# arr1# arr2#
58 sameMutableByteArray (MutableByteArray _ arr1#) (MutableByteArray _ arr2#)
59 = sameMutableByteArray# arr1# arr2#