Dear devs, I used to think that span is a function which doesn't run in bounded space. But ghc defied this understanding. The program copied below runs in bounded space with "ghc-8.2.1 -O0 main.hs; ./main" but it does not if run with "runghc-8.2.1 -O0 main.hs". Does someone have any insights on what's the optimization that is making a difference in the memory footprint of these two methods of running? Or is there a bug in ghci, and span is supposed to run in bounded space after all? Thanks, Facundo import Prelude hiding (span) import Data.List (foldl') main = case span (>0) (replicate 100000000 1) of (xs, ys) -> do print (foldl' (+) 0 xs) print (foldl' (+) 0 ys) span :: (a -> Bool) -> [a] -> ([a],[a]) span _ xs@[] = (xs, xs) span p xs@(x:xs') | p x = let (ys, zs) = span p xs' in (x : ys, zs) | otherwise = ([],xs)