A neat construct to loop in Elm without worrying about stack problems

Loops.elm

loop : a -> (a -> Bool) -> (a -> a) -> (a -> b) -> b
loop start condition update return = 
  trampoline <|
    loop' start condition update return


loop' : a -> (a -> Bool) -> (a -> a) -> (a -> b) -> Trampoline b
loop' start condition update return = 
  case condition start of 
    True -> Done (return start)
    False ->
      Continue (\() -> 
        loop' (update start) condition update return
      )


go acc n = 
  loop {acc = acc, n = n}  -- Initial state of variables
       (\{n} -> n == 0) -- stopping condition
       (\{acc, n} -> {acc = acc + 1, n = n - 1}) -- update variables
       .acc -- return function