{-|
Moves up one level in the directory tree, returning `None` if we’re already at
the root.
-}
let P =
      https://prelude.dhall-lang.org/v20.1.0/package.dhall
        sha256:26b0ef498663d269e4dc6a82b0ee289ec565d683ef4c00d0ebdd25333a5a3c98

let AbsoluteDirectory = ./Type

let ascend =
      λ(directory : AbsoluteDirectory) →
        if    ./isRoot directory
        then  None AbsoluteDirectory
        else  Some
                (   directory
                  ⫽ { directories = P.List.drop 1 Text directory.directories }
                )

let movesUpOneLevel =
        assert
      :   ascend { directories = [ "two", "one" ], file = {=}, parents = {=} }
        ≡ Some { directories = [ "one" ], file = {=}, parents = {=} }

let arrivesAtRoot =
        assert
      :   ascend { directories = [ "one" ], file = {=}, parents = {=} }
        ≡ Some ../root

let canNotCauseReparenting =
        assert
      :   ascend { directories = [] : List Text, file = {=}, parents = {=} }
        ≡ None AbsoluteDirectory

in  ascend