On Thu, Jun 11, 2020 at 1:42 AM Alexander Chen
hi,
assigment: make your own element function with the any function.
--elem with any myElemAny :: Eq a => a -> [a] -> Bool myElemAny a = any (== a)
--elem with any myElemAny' :: Eq a => a -> [a] -> Bool myElemAny' a [x]= any (== a) [x]
From a beginners perspective, the second function looks perfectly cromulent. After all, how should one indicate a list if not by enclosing it with square brackets like this, [x]?
An x might or might not be a list, but [x] surely has to be one, yes? But consider all the things that could be a list. Specifically, look at the following: 1. An empty list—which haskell denotes using []—is a list 2. [1,2,3] is a list 3. [1,1,1,…] is a list In each of the cases above, what is the value of x in [x]? Recall that haskell is a value-oriented language. Every identifier at the term-level evaluates to something that has a well-defined type.
myElemAny' compiles but throws an error because it has a non-exhaustive pattern. Could somebody tell me why the list gives the function grieveness?
thanks,
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