||| Additional functions about vectors
module Data.Vect.Extra

import Data.Vect
import Data.Fin
import Data.Vect.Elem

||| Version of `map` with access to the current position
public export
mapWithPos : (f : Fin n -> a -> b) -> Vect n a -> Vect n b
mapWithPos f [] = []
mapWithPos f (x :: xs) = f 0 x :: mapWithPos (f . FS) xs

||| Version of `map` with runtime-irrelevant information that the
||| argument is an element of the vector
public export
mapWithElem : (xs : Vect n a)
  -> (f : (x : a) -> (0 pos : x `Elem` xs) -> b)
  -> Vect n b
mapWithElem []        f = []
mapWithElem (x :: xs) f
  = f x Here :: mapWithElem xs
                (\x,pos => f x (There pos))