panic while compiling with GHC-6.4

this code snippet makes GHC-6.4 and GHCI-6.4 panic:

data DL a = DL {prev_dl::DL, el::a, next_dl::DL}

go :: DL a -> [a] -> DL a -> (DL a,DL a)
go prev [] next = (prev, next)
go prev (x:xs) next = let this = DL prev x rest
                          (rest,fin) = go this xs next
                      in this