/Prelude-v22.0.0/List/filter.dhall
Copy path to clipboardOnly keep elements of the list where the supplied function returns True
Examples
filter Natural Natural/even [ 2, 3, 5 ] ≡ [ 2 ]
filter Natural Natural/odd [ 2, 3, 5 ] ≡ [ 3, 5 ]
Source
--| Only keep elements of the list where the supplied function returns `True`
let filter
: ∀(a : Type) → (a → Bool) → List a → List a
= λ(a : Type) →
λ(f : a → Bool) →
λ(xs : List a) →
List/build
a
( λ(list : Type) →
λ(cons : a → list → list) →
List/fold
a
xs
list
(λ(x : a) → λ(xs : list) → if f x then cons x xs else xs)
)
let example0 = assert : filter Natural Natural/even [ 2, 3, 5 ] ≡ [ 2 ]
let example1 = assert : filter Natural Natural/odd [ 2, 3, 5 ] ≡ [ 3, 5 ]
in filter