我有一段代码,当给定三个点时,应该返回一个方向。我已经编写了这个解决方案,但每次尝试运行它时,都会导致GHCi冻结,所以我想知道我哪里做错了。以下是代码:
--chapter 3 question 9
data Point x y = Point x y deriving (Eq, Show)
data Vector x y = Vector x y deriving (Eq, Show)
sub (Point x y) (Point a b) = (Vector (x-a) (y-b))
dot (Vector x y) (Vector a b) = (x*a)+(y*b)
perp (Vector x y) = (Vector (-y) x)
mag (Vector x y) = sqrt (dot v v) where v = (Vector x y)
data Direction = LeftTurn | RightTurn | Straight | Reverse | Stop | Undefined
deriving (Eq, Show)
getDirection (Point a b) (Point c d) (Point e f)
| a/=c && b/=d && c==e && d==f = Stop
| a==c && b==d || c==e && d==f || e==a && f==b = Undefined
| d > 0 = LeftTurn
| d < 0 = RightTurn
| otherwise = Straight
where d = dot (sub p1 p0) (perp (sub p2 p1))
where p0 = (Point a b)
p1 = (Point c d)
p2 = (Point e f)
我看不到任何递归,所以我不明白为什么它会表现出这种行为。到目前为止,Haskell编译器一直很善于告诉我何时在做一些愚蠢的事情,但是这个代码可以正常编译。
*如果你想知道,这是《Real World Haskell》第3章的第9个问题。