def foo (a : Array Nat) : Array Nat :=
let a := a.push 0;
let a := a.push 1;
let a := a.push 2;
let a := a.push 3;
a

def main : IO UInt32 :=
do
 let a : Array Nat := Array.empty;
 IO.println (toString a);
 IO.println (toString a.sz);
 let a := foo a;
 IO.println (toString a);
 let a := a.map (fun a => a + 10);
 IO.println (toString a);
 IO.println (toString a.sz);
 let a1 := a.pop;
 let a2 := a.push 100;
 IO.println (toString a1);
 IO.println (toString a2);
 let a2 := a.pop;
 IO.println a2;
 IO.println $ (([1, 2, 3, 4].toArray).map (fun a => a + 2)).map toString;
 IO.println $ ([1, 2, 3, 4].toArray.extract 1 3);
 IO.println $ ([1, 2, 3, 4].toArray.extract 0 100);
 IO.println $ ([1, 2, 3, 4].toArray.extract 1 1);
 IO.println $ ([1, 2, 3, 4].toArray.extract 2 4);
 IO.println [1,2,3,4].toArray.reverse;
 IO.println ([] : List Nat).toArray.reverse;
 IO.println [1,2,3].toArray.reverse;
 IO.println $ [1,2,3,4].toArray.filter (fun a => a % 2 == 0);
 IO.println $ [1,2,3,4,5].toArray.filter (fun a =>  a % 2 == 0);
 IO.println $ [1,2,3,4,5].toArray.filter (fun a => a % 2 == 1);
 IO.println $ [1,2,3,4].toArray.filter (fun a => a > 2);
 IO.println $ [1,2,3,4].toArray.filter (fun a => a > 10);
 IO.println $ [1,2,3,4].toArray.filter (fun a => a > 0);
 pure 0