You can work with a mapping where you lookup all items for a list, so:
map (a !!) [0,1,2,3]
If you are however interested in the first four items, you can work with
take :: Int -> [a] -> [a]:
take 4 a
especially since looking up by an index (with
(!!)) is not a common operation in Haskell: this is unsafe since it is not guaranteed that the index is in bounds. Most list processing is done with functions like
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