Il 06 marzo 2021 alle 09:53 Galaxy Being ha scritto:
I've got this example from the Internet
import Data.List import Data.Maybe
firstFactorOf x | m == Nothing = x | otherwise = fromJust m where m =(find p [2..x-1]) p y = mod x y == 0
-- myIndex :: [a] -> Int -> Maybe a myIndex [] _ = Nothing myIndex (x:xs) 0 = Just x myIndex (x:xs) n = myIndex xs (n-1)
I would like the Just x in the second block to actually be fromJust x as in the first block, i.e., I want a number returned, not a Just typed object. I've tried changing Just x to fromJust x but get the error when I try to use it
What would happen in the `Nothing` case? If an error is fine with you: myUnsafeIndex :: [a] -> Int -> a myUnsafeIndex as n = case myIndex as n of Nothing -> error "Chiare, fresche et dolci acque" -- or maybe return -1? Idk Just r -> r What have you written instead
Also, my type declaration seems to be wrong too, but I don't see why.
It compiles fine here, even if I remove the comment from `myIndex` signature —F