Fill in the '???' with the correct code fragment such that

Expected Result: [2, 4, 6]

Question

Fill in the '???' with the correct code fragment such that

Expected Result: [2, 4, 6]

BlackTom AI · Accepted Answer

First, examine what the code is trying to do: filter a list to keep only those elements that satisfy a predicate, so the predicate must be a function that takes an element (a number in this case) and returns a Bool.
Option 1: (\x -> x `mod` 2 == 0)
This defines an anonymous function that takes x and checks if x modulo 2 equals 0. That matches the standard definition of even numbers and will produce [2,4,6] when applied to [1,2,3,4,5,6]. Therefore, this option is correct.
Option 2: (\x -> x `mod` 2 /= 0)
This is the negation of the correct condition; it keeps odd numbers (since odd numbers have mod 2 equal to 1, which is /= 0). This would yield [1,3,5], not the desired result. So this is incorrect.
Option 3: x `mod` 2 /= 0
This expression lacks a parameter to take the list element. In Haskell, filter expects a function of one argument; writing this bare expression is not a valid predicate by itself. It will not typecheck as a predicate function for filter. So this is incorrect.
Option 4: x `mod` 2 == 0
Similar to option 3, this is a boolean expression that depends on x but there is no lambda or function abstraction to supply x. As a standalone value, it’s not a valid predicate for filter. This is incorrect.

CPT_S-355-PULLM-1-LEC Scheduled Quiz 1

Fill in the '???' with the correct code fragment such that Expected Result: [2, 4, 6]

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