Dear all, I just started to learn Haskell with learnyouahaskell.com and at the very beginning, I met a strange issue with following simple function: -- why does work with "toZero 10" but not for "toZero -10"?toZero :: (Integral t) => t -> [t]toZero 0 = [0]toZero x = if x > 0 then x : toZero (x - 1) else x : toZero (x + 1) This function works as expected for positive arguments, e.g., "toZero 10" gives me [10,9,8,7,6,5,4,3,2,1,0]. However, GHCI will raise following error if I give it a negative argument, e.g., "toZero -10": *Main> toZero -10 <interactive>:12:1: Non type-variable argument in the constraint: Num (t -> [t]) (Use FlexibleContexts to permit this) When checking that ‘it’ has the inferred type it :: forall t. (Integral t, Num (t -> [t])) => t -> [t] This seems strange to me as 10 and -10 has exactly the same type "Num a => a". I've done with chapter 1~10 of learnyouahaskell.com but still has no idea on why this error. Anybody can help to explain this? Thanks a lot. Regards Zhiyi Xie