module ScrabbleScore

open System

let onePointLetter =
    [ 'A'
      'E'
      'I'
      'O'
      'U'
      'L'
      'N'
      'R'
      'S'
      'T' ]

let score word =
    word
    |> Seq.fold (fun a i ->
        let inset = List.contains (Char.ToUpper i)
        match Char.ToUpper i with
        | _ when inset onePointLetter -> a + 1
        | _ when inset [ 'D'; 'G' ] -> a + 2
        | _ when inset [ 'B'; 'C'; 'M'; 'P' ] -> a + 3
        | _ when inset [ 'F'; 'H'; 'V'; 'W'; 'Y' ] -> a + 4
        | _ when inset [ 'K' ] -> a + 5
        | _ when inset [ 'J'; 'X' ] -> a + 8
        | _ when inset [ 'Q'; 'Z' ] -> a + 10
        | _ -> a + 0) 0