module Data.SnocList

import Prelude

snoclen : ∀ a. SnocList a → Nat
snoclen {a} xs = go xs Z
  where
    go : SnocList a → Nat → Nat
    go Lin acc = acc
    go (xs :< x) acc = go xs (S acc)

snocelem : ∀ a. {{Eq a}} → a → SnocList a → Bool
snocelem a Lin = False
snocelem a (xs :< x) = if a == x then True else snocelem a xs

snocGetAt : ∀ a. Nat → SnocList a → Maybe a
snocGetAt _ Lin = Nothing
snocGetAt Z (xs :< x) = Just x
snocGetAt (S k) (xs :< x) = snocGetAt k xs

snocGetAt' : ∀ a. Int → SnocList a → Maybe a
snocGetAt' ix xs = snocGetAt (cast ix) xs