Hi,
Thankyou for the update. I will confirm the delivery as soon as I receive it.
Regards,
Sangeet
----- Original Message -----
From: "Gerold Meisinger"
To: beginners@haskell.org
Sent: Wednesday, December 29, 2010 2:57:15 PM
Subject: [Haskell-beginners] runtime error <<loop>> when using -O compile option
Hello!
I'm working on a computer game using Yampa and I get the following
runtime error:
$ myprog: <<loop>>
when compiling with
$ ghc --make MyProg.hs -o myprog -O
(without -O it works fine)
I stripped the bug down to the program below. What's funny is that the
error disappears under certain "odd circumstances" (marked as #1-#4). My
questions are:
1. How can I avoid this bug without introducing one of the "odd
circumstances"?
2. Why is it that I get this error?
3. How would you hunt down such a bug? Originally I got no clue where it
came from, so I just took the program apart piece by piece.
{-# LANGUAGE Arrows #-}
module Main (main) where
import FRP.Yampa
type ObjIn = Event () -- loop #1
--type ObjIn = Bool -- no loop #1
type ObjOut = (String, Int) -- loop #2
--type ObjOut = Int -- no loop #2
type GameObj = SF ObjIn ObjOut
testObj :: GameObj
testObj = proc hit -> do
returnA -< ("testObj", 1) -- loop #2
-- returnA -< 1 -- no loop #2
process :: [GameObj] -> SF () [ObjOut]
process objs = proc _ -> do
rec
gamestate <- par logic objs
-< gamestate -- loop #3 (recursive definition!)
-- -< [] -- no loop #3
returnA -< gamestate
logic :: [ObjOut] -> [sf] -> [(ObjIn, sf)]
logic gamestate objs = map route objs
where
route obj =
(if null (foo gamestate) then NoEvent else NoEvent, obj)
-- loop #1
-- (if null (foo gamestate) then False else False, obj)
-- no loop #1
foo :: [ObjOut] -> [ObjOut]
foo [] = []
foo objs = concat (collisions objs)
where
collisions [] = []
collisions (out:objs') =
[[out, out'] | out' <- objs, out `collide` out'] -- loop
#4
-- [[out, out'] | out' <- objs, True] -- no loop #4
collide :: ObjOut -> ObjOut -> Bool
collide (_, p) (_, p') = True -- loop #2
--collide p p' = True -- no loop #2
main :: IO ()
main = do
putStrLn . show $ embed (process [testObj]) ((), [(1.0,
Nothing)])
(Btw: I re-opened a bug report:
http://hackage.haskell.org/trac/ghc/ticket/2722#comment:10 )
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