{-# LANGUAGE UndecidableInstances #-}

module CLI.Orchestrator.Utils
    ( Singleton
    , rangeNP
    ) where

import Data.Kind (Constraint)

import Generics.SOP    (All, K (K), NP, Top)
import Generics.SOP.NP (ana_NP)

type Singleton :: [k] -> Constraint
class Singleton a where
instance Singleton '[x] where

-- | [0..n] but for NP and the `n` is derived from `xs`.
rangeNP :: All Top xs => NP (K Int) xs
rangeNP = ana_NP f (K 0)
  where
    f :: K Int (y : ys) -> (K Int y, K Int ys)
    f (K i) = (K i, K $ i + 1)