Given the following definition of doubleEvens

when you invoke it as follows

what is the result?

Question

Given the following definition of doubleEvens

when you invoke it as follows

what is the result?

BlackTom AI · Accepted Answer

Let's walk through how doubleEvens processes the input step by step so each option can be evaluated clearly.
Option 1: "[2, 4, 6, 8]". This would be the result if we mapped x * 2 over the entire input list without filtering out odd numbers first. Since the function filters even numbers only, this would be incorrect because 1 and any odd elements would still be present in the input, and their doubling would not be produced in this ordering. Therefore, this option misrepresents the effect of the filter stage.
Option 2: "[4, 8]". The function first filters the list to keep elements where x mod 2 == 0, i.e., the even numbers. Starting with [1, 2, 3, 4], the filter yields [2, 4]. Then the map (\x -> x * 2) is applied to that filtered list, producing [4, 8]. This matches the sequential application of filter followed by map exactly, so this option is a correct representation of the result.
Option 3: "[1, 2, 3, 4]". This would occur if we mapped x * 2 over the original list, or if there were no transformations at all. Neither is the case here, because the filter removes odd numbers before mapping, so the original list cannot survive intact to the output. Hence this option is incorrect.
Option 4: "map doesn't have enough arguments error". The lambda in map has a well-formed single-argument function (\x -> x * 2) and map is applied to the list produced by filter. There is no arity error in this expression; the code typechecks and evaluates to a list. Therefore, this option describes a runtime or type error that does not occur here and is incorrect.

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

Given the following definition of doubleEvens when you invoke it as follows what is the result?

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