좌표 목록으로 작업하고 싶습니다 [Haskell] (I want to work with a list of coordinates [Haskell])

문제 설명

좌표 목록으로 작업하고 싶습니다 [Haskell] (I want to work with a list of coordinates [Haskell])

좌표 목록으로 작업해야 하므로 이미 다음과 같은 유형을 만들었습니다.

type Pont = (Float, Float)

그리고 얻은 점에서 계산된 Float 목록을 반환해야 합니다. 지금까지 한 작업:

szamol :: Pont ‑> Float
szamol 0.0 = 0.0
szamol (x,y) = 10^(1/2)*((x^2)+(y^2))

ossz :: [Pont] ‑> [Pont]
ossz [] = []
ossz (h,t) = szamol h ++ ossz t

이 오류가 발생합니다.

ERROR "Hazi.hs":6 ‑ Cannot justify constraints in explicitly typed binding
*** Expression    : szamol
*** Type          : Pont ‑> Float
*** Given context : ()
*** Constraints   : (Integral a, Fractional a)

참조 솔루션

방법 1:

The pattern 0.0 in:

szamol 0.0 = 0.0

makes no sense. A Pont Point is a 2‑tuple of Floats, not a single Float, so you can define this as:

szamol :: Pont ‑> Float
szamol (0.0, 0.0) = 0.0
szamol (x,y) = 10^(1/2)*((x^2)+(y^2))

Using 10^(1/2) will fail, since the ^ operator expects the second operand to be of a type that is a member of the Integral typeclass. You can use 10**(1/2).

Using 10**(1/2) will give you the square root of 10 (so ≈ 3.16), and will not calculate the square root of the sum of squares.

You thus likely want to use:

szamol :: Pont ‑> Float
szamol (0.0, 0.0) = 0.0
szamol (x,y) = sqrt (x*x + y*y)

In your ossz function, you make three mistakes:

1. the return type should be Float here;
2. you sum up with (+), not with (++) and
3. the data constructor for a list "cons" is (:), not (,):

ossz :: [Pont] ‑> Float
ossz [] = []
ossz (h : t) = szamol h + ossz t

Here it might be better to use a combination of sum :: (Foldable t, Num a) => t a ‑> a and map :: (a ‑> b) ‑> [a] ‑> [b]:

ossz :: [Pont] ‑> Float
ossz = sum . map szamol

EDIT: if you want to return a list of Floats, then you can map:

ossz :: [Pont] ‑> [Float]
ossz = map szamol

or with explicit recursion:

ossz :: [Pont] ‑> [Float]
ossz [] = []
ossz (h : t) = szamol h : ossz t

(by Bery Purda、Willem Van Onsem)

참조 문서

1. I want to work with a list of coordinates [Haskell] (CC BY‑SA 2.5/3.0/4.0)