juvix/tests/Compilation/positive/test030.juvix

-- Ackermann function (higher-order definition)
module test030;

import Stdlib.Prelude open hiding {iterate};

iterate : {A : Type} → (A → A) → Nat → A → A
  -- clauses with differing number of patterns not yet supported
  -- iterate f zero x := x;
  | f zero := id
  | f (suc n) := f ∘ iterate f n;

plus : Nat → Nat → Nat := iterate suc;

mult : Nat → Nat → Nat
  | m n := iterate (plus n) m 0;

exp : Nat → Nat → Nat
  | m n := iterate (mult m) n 1;

ackermann : Nat → Nat → Nat
  | m := iterate λ {f n := iterate f (suc n) 1} m suc;

main : IO :=
  printNatLn (plus 3 7)
    >> printNatLn (mult 3 7)
    >> printNatLn (exp 3 7)
    >> printNatLn (ackermann 3 7);