/Prelude-v21.0.0/List/take.dhall

Copy path to clipboard

Truncate a list to the first n elements

Examples

take 2 Natural [ 2, 3, 5 ] ≡ [ 2, 3 ]
take 5 Natural [ 2, 3, 5 ] ≡ [ 2, 3, 5 ]

Source

--| Truncate a list to the first `n` elements
let Natural/lessThan =
../Natural/lessThan.dhall sha256:3381b66749290769badf8855d8a3f4af62e8de52d1364d838a9d1e20c94fa70c
? ../Natural/lessThan.dhall

let take
: ∀(n : Natural) → ∀(a : Type) → List a → List a
= λ(n : Natural) →
λ(a : Type) →
λ(xs : List a) →
List/fold
{ index : Natural, value : a }
(List/indexed a xs)
(List a)
( λ(x : { index : Natural, value : a }) →
λ(xs : List a) →
if Natural/lessThan x.index n then [ x.value ] # xs else xs
)
([] : List a)

let example = assert : take 2 Natural [ 2, 3, 5 ] ≡ [ 2, 3 ]

let example = assert : take 5 Natural [ 2, 3, 5 ] ≡ [ 2, 3, 5 ]

in take