What is the problem with my haskell code?-CodePudding

Implement some :: [Bool] -> Bool function that decides conditions a list of whether it has a true element. In this task, the or function its use is not permitted.

Test:
some [succ 'a' / = 'b', 1 1 / = 2, 10 <20] == True
some [succ 'a' / = 'b', 1 1 / = 2, 10> = 20] == False
some [] == False

some :: [Bool] -> Bool
some [] = False
some (False: _) = False
some (_: False) = False
some _ = True

How can I fix my code ? I do not know what is the problem.

CodePudding user response：

some :: [Bool] -> Bool
some [] = False
some (False:xs) = some xs
some (True:_) = True

The problem with your current code is that you don't recurse further if you see the first element is False. When you see a False you have to continue checking the rest of the list up until either the list is exhausted or you find a True. Whenever you find a True you can bail out early and just return a True because you don't care about the rest.

CodePudding user response：

In the pattern (x:xs), x is the first item of the list, and xs is a list of the remaining elements. Such list can not be False. It is possible a list full of False values, but not a Bool.

You some thus looks like:

some :: [Bool] -> Bool
some [] = False
some (x:xs) = x || some xs