elm/exercises/grade-school/GradeSchool.example

module GradeSchool (..) where

import Dict exposing (..)
import Result exposing (toMaybe)


-- TODO: implement these classes
-- type Grade = Int
-- type Student = String
-- type School = Dict Int List String


schoolFromList : List ( Int, String ) -> Dict Int (List String)
schoolFromList schoolList =
  List.foldl
    (\tuple -> \dict -> addStudent (fst tuple) (snd tuple) dict)
    newSchool
    schoolList


schoolToList : Dict Int (List String) -> List ( Int, List String )
schoolToList school =
  Dict.toList school


newSchool : Dict Int (List String)
newSchool =
  Dict.empty


addStudent : Int -> String -> Dict Int (List String) -> Dict Int (List String)
addStudent grade student school =
  Dict.insert grade (List.sort (student :: (studentsInGrade grade school))) school


gradeWithStudents : Int -> List String -> Dict Int (List String)
gradeWithStudents grade students =
  Dict.singleton grade (List.sort students)


studentsInGrade : Int -> Dict Int (List String) -> List String
studentsInGrade grade school =
  case (Dict.get grade school) of
    Just list ->
      list

    Nothing ->
      []