id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
2818	schedule: invalid what_next field	kkwweett	simonmar	"= internal error: schedule: invalid what_next field =

I'm studying a program which runs without trouble within ghci but fails to run well once compiled with ghc --make.

 * The program
 * The error message
 * The ways I get or not the error message

== The program == 

It is a computing of the index for which the length of the longuest sequence during a Syracuse process [(/2) if even u, (+1).(*3) if odd u] is reached. 

''boundary'' variable is the only parameter.

For instance, the program returns '''3''' for 

{{{
boundary=5
}}}

because [[BR]]
the 1-process [1->] has 0 element, [[BR]]
the 2-process [2->1] has 1 element, [[BR]]
the 3-process [3->10,5,16,8,4,2,1] has 7 elements, [[BR]]
the 4-process [4->2,1] has 2 elements and [[BR]]
the 5-process [5->16,8,4,2,1] has 5 elements [[BR]]
so the index for which the maximum is reached is '''3''' (for a length maximum of 7).

{{{
-- syracuse.hs
import Data.Array
import Data.Ord

boundary=25999
 
maximumBy g x = fst $ (foldr (maxBy g) (0,0) x)

maxBy comp x y=case (comp x  y) of
   GT -> x
   EQ -> y
   LT -> y

syrs n = a
    where a = listArray (1,n) $ 0:[ syr x | x <- [2..n]]
          syr x = if x' <= n then 1 + a ! x' else 1 + syr x'
              where x' = if even x then x `div` 2 else 3 * x + 1

main = print $ maximumBy (comparing snd)$ assocs $ syrs boundary

}}}


== The error message ==

syracuse.exe: internal error: schedule: invalid what_next field [[BR]]
    (GHC version 6.10.1 for i386_unknown_mingw32)[[BR]]
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug [[BR]]

This application has requested the Runtime to terminate it in an unusual way. [[BR]]
Please contact the application's support team for more information. [[BR]]

== The ways I get or not the error message ==

I'm running Windows XP SP3 on a ~1GHz CPU/ ~1Go RAM computer.[[BR]]
Within ghci, I'm only limited by memory (I get an *** Exception : stack overflow for boundary=140000) and I can compute up to 

{{{
boundary=130000
}}}

for which the program returns '''106239'''.

On the other hand, when I compile using

{{{
ghc --make syracuse
}}}

everything 's all right up to boundary=25998 (result:'''23529''', Exit code: 0 ) but as far as boundary>25998, the program displays the result (for instance I can get '''106239''' again) but the error message is also displayed with Exit code: 3.

"	bug	closed	normal	6.10.2	Runtime System	6.10.1	fixed	schedule	ben@…	Windows	x86		Unknown