recursion-exercise.hs

import Data.List (find)

data Family = Family
  { person :: String,
    mother :: String,
    father :: String
  }
  deriving (Show, Eq)

relatedFamilyData :: [Family]
relatedFamilyData =
  [ Family {person = "Alice", mother = "Mary", father = "John"}, -- Alice is the child of Mary and John
    Family {person = "Mary", mother = "Grace", father = "Robert"}, -- Mary is the child of Grace and Robert
    Family {person = "John", mother = "Emma", father = "Michael"}, -- John is the child of Emma and Michael
    Family {person = "Grace", mother = "Anna", father = "David"}, -- Grace is the child of Anna and David
    Family {person = "Robert", mother = "Eve", father = "James"} -- Robert is the child of Eve and James
  ]

findFamilyByName :: String -> Maybe Family
findFamilyByName name = find (\record -> person record == name) relatedFamilyData

extendedFamily :: Maybe Family -> String -> [String]
extendedFamily (Just family) to
  | not (null motherAncessors) = motherAncessors
  | not (null fatherAncessors) = fatherAncessors
  | otherwise = []
  where
    motherAncessors =
      ancessors (mother family) to
    fatherAncessors =
      ancessors (father family) to
extendedFamily Nothing _ = []

ancessors :: String -> String -> [String]
ancessors from to
  | from == to = [to]
  | not (null family) = from : family
  | otherwise = family
  where
    family = extendedFamily (findFamilyByName from) to

-- Print the list of family records
main :: IO ()
main = do
  mapM_ print (ancessors "Alice" "Emma")