// "decl" is not required, but useful in module interface

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
    | _ -> fib (n - 1) + fib n

decl fact : Int -> Int
def fact : n =
  match n with
    | 0 -> 1
    | n -> n * fact (n - 1)

decl find_prefix_hashes ('H : (#AccHash Char)) : String -> Array 'H
def find_prefix_hashes ('H : (#AccHash Char)) : 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).clone
    ; hashes.i.append str.i
  }

  return hashes
}

// ?? other default constructor symbol (instead of placeholder _), etc. ??

// seporate first and last iteration of loop ?
// previous and next iterations ?

decl find_substring : String -> String -> Array Index
def find_substring : str substr = {
  alias Hash = AccHash Char

  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 : Unit -> Bool
def is_empty =
  return 0

decl do_something : Unit -> 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 // or argument can be used

// ?? is partial application feature needed ??