strange bug

[Andreas Marth]

Hi again!   I cut the example a bit further down. Read the comments at the end of the file. --------------------------------------------------------------------------------------------------------------- >import Array > >data CM a = ZM | M (Array (Int,Int) a)  deriving (Show,Eq) > >data RD =    NB !(Double,Int) > >main  = do let arr = foo (NB (1.0,1)) >  putStr ("arr==arrS "++show (arr==arrS)++"\n") >  putStr ("arrS==arr "++show (arrS==arr)++"\n") >  putStr ("bnds arr arrS "++show ((bounds arr)==(bounds arrS))++"\n") >  putStr ("bnds +id arr arrS "++show (((bounds.id) arr)==((bounds) arrS))++"\n") >  putStr ("id +bnds arr arrS "++show (((id.bounds) arr)==((bounds) arrS))++"\n") > >foo :: RD -> Array (Int,Int) (CM Double) >foo rd = case rd of >    NB (f,p) -> h where h=hCMt [(p,listArray ((1,1),(1,1)) [f])] >   where >   --h0CMt :: Array (Int, Int) (CM Double) >   h0CMt = accumArray (\a _-> a) ZM ((1,1),(1,2)) [] >   hCMt po_arL = h0CMt // (map (\(po,ar) -> ((1,po),M ar)) po_arL) > >arrS :: Array (Int,Int) (CM Double) >arrS = listArray ((1,1),(1,2)) [M (listArray ((1,1),(1,1)) [1.0]),ZM] >-- This is the array that foo (NB (1.0,1)) shows in Hugs. >-- But (foo (NB (1.0,1)))==arrS is False. >-- All in main is only to show the strange behaviour. >-- If I write NB (f,p) -> hCMt [(p,listArray ((1,1),(1,1)) [f])] instead of line 16 >-- the bug disappears. That is also the reason why I have to keep the data declaration RD. >-- If I put the type signature of line 18 in scope the bug also disappears. >-- If I write >-- hCMt po_arL = (accumArray (\a _-> a) ZM ((1,1),(1,2)) []) // (map (\(po,ar) -> ((1,po),M ar)) po_arL) >-- instead of line 19 and 20 it also vanishes. >-- So I thing now it is the shortest example that I can find. (Apart from deleting main.)

bug1.hs