decl sum ('A : #Add) : 'A -> 'A -> 'A
def sum : a b = a + b

decl fib : Int -> Int
def fib : n =
  match n with
    | 0 | 1 -> 1
    | n ? n > 1 -> fib: (n - 1) + fib: n
    | _ -> error: "n must be positive"

decl fact : Int -> Int
def fact : n =
  match n with
    | 0 -> 1
    | n ? n > 0 -> n * fact: (n - 1)
    | _ -> error: "n must be positive"

decl find_prefix_hashes ('H : (#AccHash Char)) : String -> (Array 'H)
def find_prefix_hashes : str = {
  var hashes = (Array 'H).new: (str.size: + 1)

  ; hashes`0 = 'H.of: str`0
  for i in 1--hashes.size: do {
    ; hashes`i = hashes`(i - 1)
    ; hashes`i.append: str`i
  }

  return hashes
}

alias Hash = (AccHash Char)

decl find_substring : String -> String -> (Array Index)
def find_substring : str substr = {
  var result = (Array Index).empty:

  const str_hashes = find_prefix_hashes Hash: str
  const substr_hash = Hash.of: substr

  for i in 0--(str_hashes.size: - substr.size:) do {
    const part_hash = Hash.diff: str_hashes`(i + substr.size:) str_hashes`i

    if part_hash == substr_hash then {
      ; result.push: i
    }
  }

  return result
}

decl is_empty : -> Bool
def is_empty = 0

decl do_something : -> Unit
def do_something =
  IO.print: "Hello World!"

decl mul : Int -> Int -> Int
def mul : x y = x * y

decl mul_10 : Int -> Int
def mul_10 = mul: 10