stop_or_call n, f: (Nat -> Nat), g: (Nat -> Nat) =
if n <= 0:
do 1
do:
m = n - 1
assert m in Nat
g (f m)
fact(n: Nat): Nat =
stop_or_call n, fact, (r, ) -> r * n
assert fact(5) == 120
iterate(_, 0, x) = x
iterate(f, n: Int, x) = iterate f, n-1, f x
assert iterate((x -> x + 1), 5, 0) == 5
assert iterate((x -> x + "a"), 5, "b") == "baaaaa"
push! x: Str =
res = ![]
res.push! x
for! [], a =>
res.extend! push! a
res
assert push!("a") == ["a"]