Listen brahs. I have a dirty anus that needs cleaning: Java. I learned Java as my first language in school and now that I learned Scheme and am learning Haskell, I figured I may as well not let that go to waste and learn Scala. Is it simple to go from Java to Scala? Or is the syntax strange in some places. Because I looked over some code snippets and it seemed decent.
-- shortcuts
type One = Succ Zero
type Two = Succ One
type Three = Succ Two
type Four = Succ Three
-- example list
list1 :: Cons Three (Cons Two (Cons Four (Cons One Nil)))
list1 = undefined
-- utilities
numPred :: Succ a -> a
numPred = const undefined
class Number a where
numValue :: a -> Int
instance Number Zero where
numValue = const 0
instance Number x => Number (Succ x) where
numValue x = numValue (numPred x) + 1
numlHead :: Cons a b -> a
numlHead = const undefined
numlTail :: Cons a b -> b
numlTail = const undefined
class NumList l where
listValue :: l -> [Int]
instance NumList Nil where
listValue = const []
instance (Number x, NumList xs) => NumList (Cons x xs) where
listValue l = numValue (numlHead l) : listValue (numlTail l)
-- comparisons
data Less
data Equal
data Greater
class Cmp x y c | x y -> c
instance Cmp Zero Zero Equal
instance Cmp Zero (Succ x) Less
instance Cmp (Succ x) Zero Greater
instance Cmp x y c => Cmp (Succ x) (Succ y) c
-- put a value into one of three lists according to a pivot element
class Pick c x ls eqs gs ls' eqs' gs' | c x ls eqs gs -> ls' eqs' gs'
instance Pick Less x ls eqs gs (Cons x ls) eqs gs
instance Pick Equal x ls eqs gs ls (Cons x eqs) gs
instance Pick Greater x ls eqs gs ls eqs (Cons x gs)
-- split a list into three parts according to a pivot element
class Split n xs ls eqs gs | n xs -> ls eqs gs
instance Split n Nil Nil Nil Nil
instance (Split n xs ls' eqs' gs',
Cmp x n c,
Pick c x ls' eqs' gs' ls eqs gs) =>
Split n (Cons x xs) ls eqs gs