Hello, When benchmarking my new vector-bytestring[1] package I discovered that building the following program causes GHC to go into, what seems to be, an infinite loop: import Data.Vector (Vector) import qualified Data.Vector.Generic as VG main = print $ VG.foldl f z (VG.fromList [] :: Vector Int) f = flip (:) z = [] I build it with: $ ghc --make vectorGHCloop.hs -O2 It compiles fine without the -O2 or if you specify -fno-enable-rewrite-rules. So it's probably a loop in a rule somewhere. Note that the program also builds fine when I change the 'f' and 'z' to: f = flip (:) z = [] I use vector-0.9 and ghc-7.2.1. Regards, Bas [1] https://github.com/basvandijk/vector-bytestring