interps.pul

\primzero primsucc ->

(\interp ->

interp (\f -> f) (\f x -> f x) (\x -> x)

) (quote ((\let -> 
  -- error
  let ((\x -> x x) (\x -> x x)) \error ->
 
  -- church numerals
  let (\f x -> x) \zero ->
  let (\n f x -> f (n f x)) \succ ->

  -- scott lists
  let (\n c -> n) \nil ->
  let (\x xs -> \n c -> c x xs) \cons ->

  let (\l -> l error (\x xs -> x)) \head ->
  let (\l -> l error (\x xs -> xs)) \tail ->
  
  let (\xs n -> head (n tail xs)) \index ->

  -- scott debruijn
  let (\f   -> \l a v -> l f)   \fun ->
  let (\t u -> \l a v -> a t u) \app ->
  let (\n   -> \l a v -> v n)   \var ->
  
  -- recursion
  let (\f -> (\x -> x x) (\x -> f (x x))) \fix ->

  -- interpreter
  let (fix (\interp env term -> term (\body    -> \x -> interp (cons x env) body)
                                     (\fun arg -> interp env fun (interp env arg))
                                     (\var     -> index env var)) nil)
    \interpreter ->
    
  interpreter (fun (fun (var (succ zero)))) primzero error

) (\def body -> body def)))

-- vim: ft=haskell :