fun findGrade _    []          = "No grade"
  | findGrade name ((n,g)::xs) =
    if name = n then
        g
    else
        findGrade name xs;

fun findGradeBetter _    []          = NONE
  | findGradeBetter name ((n,g)::xs) =
    if name = n then
        SOME g
    else
        findGradeBetter name xs;

fun passingClass name grades =
    let
        fun passHelper  NONE      = false
          | passHelper (SOME "F") = false
          | passHelper (SOME "f") = false
          | passHelper _          = true;
    in
        passHelper (findGradeBetter name grades)
    end;                

fun passingClass name grades =
    case findGradeBetter name grades of
        NONE       => false
      | (SOME "F") => false
      | (SOME "f") => false
      | _          => true;

fun passingClass name grades =
    let
        fun passHelper  NONE      = false
          | passHelper (SOME x)   = 
            if x = "F" orelse x = "f" then
                false
            else
                true;

    in
        passHelper (findGradeBetter name graes)
    end;