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La ce folosim operatorul !! (dublu semn de exclamare) ?

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Este folosit pentru a extrage al n-lea element dintr-o lista, n fiind numar intreg.

Aruncati o privire aici:

Prelude> :t (!!)

(!!) :: [a] -> Int -> a

Prelude> (!!) [1,2,3,5] 0

1

Prelude> (!!) [1,2,3,5] 1 2


Prelude> (!!) [1,2,3,5] 2

3

Prelude> (!!) [1,2,3,5] 3

5

Prelude> (!!) [1,2,3,5] 4

Program error: Prelude.!!: index too large