{-# OPTIONS_GHC -fglasgow-exts -O -ddump-prep #-} module Max(result) where foo ys = foldr (\x xs -> x : reverse xs) [] ys result xs = let stuff = [1, 1, 1, 1, 1, 1] in foo (reverse stuff) -- What used to happen is that foldr got expanded by main simplification -- and the resulting "go" function got floated out but because we manufactured -- a new binder for it in newPolyBndrs we would lose its demand signature! -- This means that the later application of it in result did not use call by value :-( -- Eyeball test: -- Ensure that Max.poly_go has a demand signature -- Ensure that we use call by value to call Max.poly_go in result -- i.e. the call to Max.poly_go inside Max.result looks like this: -- -- case GHC.List.poly_rev @ t1_a6x sat_seb (GHC.Base.[] @ t1_a6x) -- of sat_sed { __DEFAULT -> -- Max.poly_go @ t1_a6x sat_sed -- } } in