sum-digits.hm.hs

module Fib using: Platform where
  
  open Platform Prelude       expose [+, parse, as-string, ~]
  open Platform List          expose [zip:using:, map:, take:, filter:, sum]
  open Platform IO            expose [read-line, print]

  -- Typing things is currently cumbersome, but the type inference algorithm should catch 90% of this
  let (Num a) => String -> a ::
  x as-number = x parse

  -- ~ is cons.
  let fibs = 0 ~ 1 ~ fibs zip: fibs tail using: +
  let n sum-digits = n as-string map: as-number |> sum
  
  let main: _ = read-line >>= { x => fibs filter: even
                                       |> take: x as-number
                                       |> sum
                                       |> sum-digits
                                       |> print
                              }

end