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-- !! Make sure that state threads don't escape
-- !! (example from Neil Ashton at York)
--
module ShouldFail where
import GHC.Arr
import Control.Monad.ST ( runST )
type IndTree s t = STArray s (Int,Int) t
itgen :: Constructed a => (Int,Int) -> a -> IndTree s a
itgen n x =
runST (
newSTArray ((1,1),n) x)
itiap :: Constructed a => (Int,Int) -> (a->a) -> IndTree s a -> IndTree s a
itiap i f arr =
runST (
readSTArray arr i >>= \val ->
writeSTArray arr i (f val) >>
return arr)
itrap :: Constructed a => ((Int,Int),(Int,Int)) -> (a->a) -> IndTree s a -> IndTree s a
itrap ((i,k),(j,l)) f arr = runST (itrap' i k)
where
itrap' i k = if k > l then return arr
else (itrapsnd i k >>
itrap' i (k+1))
itrapsnd i k = if i > j then return arr
else (readSTArray arr (i,k) >>= \val ->
writeSTArray arr (i,k) (f val) >>
itrapsnd (i+1) k)
itrapstate :: Constructed b => ((Int,Int),(Int,Int)) -> (a->b->(a,b)) -> ((Int,Int)->c->a) ->
(a->c) -> c -> IndTree s b -> (c, IndTree s b)
itrapstate ((i,k),(j,l)) f c d s arr = runST(itrapstate' i k s)
where
itrapstate' i k s = if k > l then return (s,arr)
else (itrapstatesnd i k s >>= \(s,arr) ->
itrapstate' i (k+1) s)
itrapstatesnd i k s = if i > j then return (s,arr)
else (readSTArray arr (i,k) >>= \val ->
let (newstate, newval) = f (c (i,k) s) val
in writeSTArray arr (i,k) newval >>
itrapstatesnd (i+1) k (d newstate))
-- stuff from Auxiliary: copied here (partain)
sap :: (a->b) -> (c,a) -> (c,b)
sap f (x,y) = (x, f y)
fap :: (a->b) -> (a,c) -> (b,c)
fap f (x,y) = (f x, y)
nonempty :: [a] -> Bool
nonempty [] = False
nonempty (_:_) = True
-- const :: a -> b -> a
-- const k x = k
-- id :: a -> a
-- id x = x
compose :: [a->a] -> a -> a
compose = foldr (.) id
class Constructed a where
normal :: a -> Bool
instance Constructed Bool where
normal True = True
normal False = True
instance Constructed Int where
normal 0 = True
normal n = True
instance (Constructed a, Constructed b) => Constructed (a,b) where
normal (x,y) = normal x && normal y
-- pair :: (Constructed a, Constructed b) => a -> b -> (a,b)
-- pair x y | normal x && normal y = (x,y)
instance Constructed (Maybe a) where
normal Nothing = True
normal (Just _) = True
just :: Constructed a => a -> Maybe a
just x | normal x = Just x
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