I m 试图在每个人都有性或姓名的情况下创造个人类型。
data Sex = Sex Char deriving Show
male = Sex M
female = Sex F
data Name = Name [Char] deriving Show
data Person = Person {
Sex :: Sex,
Name :: Name
} deriving (Show)
当我试图在格西里装上这段话时,我才发现无益的错误:输入中的错误。
我在这里做了什么错误?
问题在于你在记录中使用了上一级案件。 守则应着眼于:
data Person = Person { sex :: Sex, name :: Name }...
守则似乎至少是编纂的。 由于“性别”和“姓名”不是类型(尽管“Sex”和“Name”),因此,你不能将第一封信函列为上。
I m trying my hand at Euler Problem 4 in Haskell. It asks for that largest palindrome formed by multiplying two three-digit numbers. The problem was simple enough, and I thought my Haskell-fu was up ...
Can anybody explain how does foldr work? Take these examples: Prelude> foldr (-) 54 [10, 11] 53 Prelude> foldr (x y -> (x+y)/2) 54 [12, 4, 10, 6] 12.0 I am confused about these executions....
How can I efficiently implement a list data structure where I can have 2 views to the head and end of the list, that always point to a head a tail of a list without expensive calls to reverse. i.e: ...
I am doing problem 61 at project Euler and came up with the following code (to test the case they give): p3 n = n*(n+1) `div` 2 p4 n = n*n p5 n = n*(3*n -1) `div` 2 p6 n = n*(2*n -1) p7 n = n*(5*n -3)...
I ve just started learning about Functional Programming, using Haskel. I m slowly getting through Erik Meijer s lectures on Channel 9 (I ve watched the first 4 so far) and in the 4th video Erik ...
The type of the Prelude function flip is: flip :: (a -> b -> c) -> b -> a -> c I.e., it takes one binary function and two arguments. The type of the Prelude function id is: id :: a -...
group :: Ord a => [(a, [b])] -> [(a, [b])] I want to look up all pairs that have the same fst, and merge them, by appending all the list of bs together where they have the same a and discarding ...
I want to do a popen() / python s subprocess.communicate from Haskell - start a program, give it stdin, and get its stdout/stderr. What s the most direct / Haskellish way to do this?