> I am having a bizarre Haskell problem that I am having difficulty > debugging. I am not positive this is a compiler problem, but > my results > are not making any sense. > > I have attached a few source files which compiled with ghc-5.04.2 > running under Win95. The files were compiled as: > > ghc -c DFT.lhs > ghc -c FFT1.lhs > ghc -c FFT2.lhs > ghc -c Main1.hs > ghc -c Mail2.hs > ghc -o test1 Main1.o FFT1.o DFT.o > ghc -o test2 Main2.o FFT2.o DFT.o > > Running test1 gives the following results (the last line is wrong): > > foo 19: [1,2,4,8,16,13,7,14,9,18,17,15,11,3,6,12,5,10] > rader1 19: [1,2,4,8,16,13,7,14,9,18,17,15,11,3,6,12,5,10] > foo 23: [1,5,2,10,4,20,8,17,16,11,9,22,18,21,13,19,3,15,6,7,12,14] > rader1 23: [1,5,2,10,4,20,8,17,16,11,9,22,18,21,1,4,8,18,22,6,19,2] > > Running test2 gives the following results (these are the results I > expect): > > foo 19: [1,2,4,8,16,13,7,14,9,18,17,15,11,3,6,12,5,10] > rader1 19: [1,2,4,8,16,13,7,14,9,18,17,15,11,3,6,12,5,10] > foo 23: [1,5,2,10,4,20,8,17,16,11,9,22,18,21,13,19,3,15,6,7,12,14] > rader1 23: [1,5,2,10,4,20,8,17,16,11,9,22,18,21,13,19,3,15,6,7,12,14]
Your problem is that rader1 has different types in FFT1 and FFT2: ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 5.04.2, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. :Prelude> :l FFT1 Skipping DFT ( DFT.lhs, DFT.o ) Skipping FFT1 ( FFT1.lhs, ./FFT1.o ) Ok, modules loaded: FFT1, DFT. Prelude FFT1> :t rader1 forall a b. (Integral a, GHC.Arr.Ix a, Num (Data.Complex.Complex b), RealFloat b) => GHC.Arr.Array a (Data.Complex.Complex b) -> a -> [a] Prelude FFT1> :t rader1 (gendata 23) 23 [Int] Prelude FFT1> :l FFT2 Skipping DFT ( DFT.lhs, DFT.o ) Skipping FFT2 ( FFT2.lhs, ./FFT2.o ) Ok, modules loaded: FFT2, DFT. Prelude FFT2> :t rader1 forall a t. (Integral a, GHC.Arr.Ix a) => t -> a -> [a] Prelude FFT2> :t rader1 (gendata 23) 23 forall a. (Integral a, GHC.Arr.Ix a) => [a] So in FFT2, defaulting will force the type variable a to Integer, whereas in FFT1 the type has already been forced to Int. I imagine that with Int you're getting some overflow, leading to the incorrect results. Moral of this story: type signatures can help to avoid unexpected behaviour... Cheers, Simon _______________________________________________ Glasgow-haskell-bugs mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
