Atelier Haskell

Friends.hs

module Friends where

data Relation = Friend | Cousin | Professor deriving (Show, Eq)
data Person = Person String deriving (Show, Eq)
data Fact = Fact Relation (Person, Person) deriving (Show, Eq)
data Graph = Graph [Fact] deriving Show

areFriends :: Graph -> Person -> Person -> Bool
areFriends (Graph facts) person1 person2 = 
  (not . null) [(p1, p2) | Fact Friend (p1, p2) <- facts, p1 == person1 && p2 == person2]
  
  
insertFriends :: Person -> Person -> Graph -> Graph
insertFriends person1 person2 (Graph facts) =
  Graph (facts ++ [Fact Friend (person1, person2), Fact Friend (person2, person1)])
  
emptyGraph :: Graph
emptyGraph =  Graph []

FriendsTest.hs

import Test.HUnit
import Friends (Person (..), areFriends, insertFriends, emptyGraph)

test1 = TestCase $ do 
    let stephan = Person "Stephan"
    let jb = Person "Jean-Baptiste"
    let bruno = Person "Bruno"
    let graph =  ((insertFriends bruno jb) . 
                 (insertFriends jb stephan)) emptyGraph
    
    assertBool "Stephan and JB should be friend" (areFriends graph stephan jb)
    assertBool "JB and Stephan should be friend" (areFriends graph jb stephan)
    assertBool "Bruno and JB should be friend" (areFriends graph bruno jb)
    assertBool "Bruno should not be friend with Stephan" (not (areFriends graph stephan bruno))



tests = test [
  TestLabel "test1" test1
  ]

main = runTestTT tests