TCls3.purs

module Mini.TCls3 (class Two, dos, class Tri, tres, class Quad, quattro) where

class Zero where
    zilch :: Boolean

class One where
    uno :: Int -> Number
    ein :: Number -> Boolean -> Int

class One <= Two a where
    dos :: a -> Int

class (Two a, Zero) <= Tri b a where
    tres :: a -> b

class (Zero, Two a) <= Quad a b where
    quattro :: b -> a

instance inst0 :: Zero where
    zilch = true

instance inst1 :: One where
    uno _ = 1.23
    ein _ true = 321
    ein _ _ = 123

TClsImpl3.purs

module Mini.TClsImpl3 where

import Prelude ((*))

import Mini.TCls3

newtype NtTwo = NT2 Int

newtype NtTri = NT3 String

newtype NtFour a = NT4 a

instance inst2 :: Two NtTwo where
    dos (NT2 i) =
        i * 2

instance inst3 :: Tri NtTri NtTwo where
    tres (NT2 0) =
        NT3 "eq-0"
    tres _ =
        NT3 "gt-0"

instance inst4 :: (Two a) => Quad a (NtFour a) where
    quattro (NT4 a) =
        a