FizzBuzz

FizzBuzz.hs

{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE StandaloneKindSignatures #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE GADTs #-}

module FizzBuzz where

import Data.Singletons.TH
import Data.Singletons.Prelude
import Data.Singletons.TypeLits

$(singletons [d|
  type Divisible n by = Mod n by == 0

  type FizzBuzzElem :: Nat -> Symbol
  type FizzBuzzElem n =
      If
        (Divisible n 15)
        "FizzBuzz"
        ( If
            (Divisible n 3)
            "Fizz"
            ( If
                (Divisible n 5)
                "Buzz"
                (Show_ n)))

  |])

type FizzBuzz n = Fmap FizzBuzzElemSym0 (EnumFromTo 1 n)

-- |
-- >>> fizzBuzz @10
-- "[FizzBuzz,1,2,Fizz,4,Buzz,Fizz,7,8,Fizz]"
fizzBuzz :: forall (n :: Nat). (KnownSymbol (Show_ (FizzBuzz n))) => String
fizzBuzz = symbolVal (Proxy @(Show_ (FizzBuzz n)))