a3/code/Generics/GenHylo.icl

   1 implementation module GenHylo
   2
   3 import StdGeneric, GenMap, StdFunc
   4
   5 :: Fix f = In (f .(Fix f))
   6
   7 Out :: !u:(Fix v:a) -> v:(a w:(Fix v:a)), [u <= w]
   8 Out (In x) = x
   9
  10 hylo :: ((.f .b) -> .b) (.a -> (.f .a)) -> (.a -> .b) | gMap{|*->*|} f
  11 hylo consume produce = consume o gMap{|*->*|} (hylo consume produce) o produce
  12
  13 cata :: (u:(f .a) -> .a) -> (Fix u:f) -> .a | gMap{|*->*|} f
  14 cata f = hylo f Out
  15
  16 ana :: (.a -> u:(f .a)) -> .a -> (Fix u:f) | gMap{|*->*|} f
  17 ana f = hylo In f
  18